Created: February 19, 2002
Updated: May 16, 2008

Frequently Asked Questions

Table of Contents

1. Introduction
2. Internet Woodworking Forums
3. Kit Cyclones & Blowersw
4. General Site Questions
5. Getting Started
6. Venting Outside
7. Maintenance
8. Blowers and Impellers
9. Motors
10. Dust Collectors
11. Cyclone General Information
12. Dust Masks and Respirators
13. Filters and Dust Bags
14. Carving
15. Metal Working

Introduction

At one time I maintained a list of frequently asked questions (FAQs) that would take hours to read. During the repeated rewrites of these pages, that technical information went back to the pages that deal with each of topic. The below FAQs now address the non-technical issues.

Internet Woodworking Forums

1. Bill, I am an old hobbyist woodworker idling down my practice as a pulmonary physician with hopes to soon retire. You cannot believe the numbers of younger hobbyist woodworkers and their family members who come in with serious sensitivities to a wide range of trees that don’t even grow in this country. Worse, a good many of my patients that develop serious respiratory problems later in life at some point had high exposures to fine wood dust. I believe airborne wood dust is responsible for far more problems than we realize, but these problems like asbestos exposure occur so many decades later it is very difficult to tie them to a particular thing. With research money real tough to find, I seriously doubt we are going to see any studies in the near future to determine how big this problem really is.
   
   I recently starting spending time on the Internet woodworking forums and read a few of your posts on the Saw Mill Creek forum. I first heard of you about four years ago from one of my woodworker patients. Reading your information and web pages went on my someday pile buried under my required reading to keep up with my specialty. After reading your posts I spent my weekend reading over your Cyclone and Dust Collection Research web pages. You need to get this stuff rewritten without all the duplication and cutesy flavoring. Still, what you have to say is by far the best that I have read anywhere and thank you for your efforts.
   
   As a pulmonary physician I fully agree with your Doctor's Orders pages. Moreover this is a fairly small specialty where there are just not that many experts, so I made an educated guess and called the top respiratory specialist in your area. We had a great chat as he is also a woodworker hoping to retire to this hobby in another ten years or so. And yes, he told me he is your doctor. He called you a PITA, way too headstrong and smart, and one of the finest people he knows. He asked me to give you his regards for sticking with this for so long while so many continue to badger you.
   
   In our conversation we both agreed after more research we will see wood dust getting classified as more dangerous than smoking. The chemicals in and associated with wood cause too many serious health problems. We also both believe wood causes far more long term problems that do not show up until our later years. Wood cell walls are like little cups similar to the silica (glass) coating that makes diatomaceous earth used in swimming pool filters so unhealthy to breathe. Our bodies build up tissue around these fine sharp particles leading to fibrosis and reduced respiratory capacity. This damage builds over time and is not an issue until we either get sick or get older. I understand why you doctor friend will not let you use his name on your site. As a teaching researcher I also have to be very careful to only put my name on peer reviewed articles and studies.
   
   Anyhow, I was unhappy to see you were evicted from the Saw Mill Creek woodworking forum after some of the best comments on wood dust collection I have ever seen. Please let me know if you want me to write the forum owner or if is there anything I can do to get you to go back onto that forum.
   Thank you for your kind words of support. I’ve received a number of letters from other pulmonary specialists saying very similar things.
   
   Although Internet forums are a great place to share information they are also a very effective way for vendors to promote products. In August 2004 I was asked by the president of one of the leading small shop cyclone companies to go to work for his firm. I would work from home as a private consultant providing web page posts plus would need to change my web pages to recommend his firm. In trade he promised $2,000 a month base salary, 5¢ for every visit to one of my pages or posts that ended up with someone going directly to their vendor pages, plus 10% commissions on all sales where someone bought from his firm after visiting either one of my web pages or forum posts. He explained their Internet tracking let his firm and me see whenever someone went from my pages or posts without needing for me to include either a link or tracking ID. In short, he guaranteed I would make at least $6,000 a month, or we could go to war. If I refused and continued to give my free support to Clear Vue Cyclones, he was going to instruct his group of paid posters to do all in their power to destroy the credibility of my web pages and of me personally. Moreover, he was going to instruct his attorneys to tie me up indefinitely in expensive court cases. I declined his offer and contacted my attorney. My attorney had me remove every direct reference to this firm including my easily verified air volume and air quality testing that showed this firm has long been a fraud. That sadly diluted the value of these pages, but at least keeps them up instead of closed down by court order until we can finish slugging it out in court. Clearly there is both a strong positive and negative side to these forums when it comes to their financial impact, but I don’t want to waste my time and money getting involved in all the drama.
   
   Soon after those threats I got severe warnings on both the WoodNet and Saw Mill Creek forums, plus Pentz bashing became popular on a few of the forums. Meanwhile Wood Magazine begged me to post more. Woodnet eventually tossed me off and recently so did Saw Mill Creek. Woodnet gets considerable advertising money from this vendor and Saw Mill Creek allows this vendor to pay one of its lead moderators. I found (see next question) it takes a lot of time and money to run a forum with much of that time spent babysitting adults. Most forums depend upon volunteer forum moderators. A few are lucky enough to get dedicated retirees or disabled on pensions, but most end up having to depend on either a huge number of volunteers or use vendor paid shills who stay logged into the main forums every day anyway. The forum owners try to look the other way when these people do their selling as long as they do so quietly. Two different firms tried to hire me to replace one of the most prolific Saw Mill Creek forum moderators because he did a poor job sharing accurate information. I already give way too much of my life to keep up my web pages and respond to well over four hours a day of emails. I don’t have the time or patience to post on forums, so no please don’t go out of your way to respond to Saw Mill Creek. Even if they let me return, I rarely would have time to post.

2. I know you have been posting on the various Internet woodworking forums since back when they were news groups and rumor has it you even were a moderator if not creator of one of the larger early forums. How much of this is true and why don’t I see you posting much anymore?
   I started using the Internet, email, and news groups when in the military and as a university instructor back in the middle seventies. So yes, I have made a few woodworking posts over the years. Yes, I also helped form one of the early Internet woodworking forums then moved on quickly not liking the baby sitting required to keep adults behaving civilly toward each other. And no, as much as I like most of the people that visit the various woodworking forums, I don’t particularly care to post dust collection information on forums. Most of these forums work well for simple question and simple answer types of communication, but when more is involved, like dust collection, responding takes lots of work and typing. Many woodworkers have not taken the time to learn the basics of fine dust collection. That means any time I post I get buried in a ton of questions that are far better answered here on my web pages. Worse, many misinterpret what I say without long winded explanations. Writing has never come easy to me and is now physically painful due to health issues. Dust collection is also a very dicey topic because almost every hobbyist vendor that sells tools and dust collection systems is selling "chip collection" technology that works poorly when it comes to fine dust collection. People do not like hearing they were stupid just like me. They like even less learning that the expert figures we have long trusted badly let us down when it comes to giving good dust collection advice and accurate dust collection testing. I spent a small fortune on the top recommended hobbyist dust collectors, cyclones, fine filters, air cleaner, and ducting system that made my shop air worse than if I had stayed with my broom and dustpan with a strong fan running in an open doorway. Also, in spite of preferring to be just one of “the guys” on the forums, my attorney after fending off six threatened suits, has made it clear that because of the popularity of my web pages, what I say carries far more weight than most who post on dust collection. My comments can and do greatly impact sales and the well being of many people. Giving quick dust collection answers without tons of backup information and the exceptions has inadvertently hurt a few of those firms I respect and support. For these reasons, I keep my posting to a bare minimum.

3. Okay, so you should not post on the woodworking forums, but why do you keep letting the same few people bash you again and again on these same Internet woodworking forums?
   My personal feeling is that any group whose members tolerate this kind of bashing is a social club where I choose not to spend my time. As I said before I helped start and moderate one of the early woodworking forums. I discovered that any forum that allows people to join freely without a real name and email address tied to their home ISP is a forum that will need a lot of babysitting. Sad as it is to admit, our forums that started out as a good way to share knowledge and entertainment, have become overrun by vendor paid forum administrators and shills whose livelihoods depend upon their making posts that promote vendor products, attack competition, and cause threads that can hurt their employer to quickly get erased. Forum administration is a thankless pain in the tail job that consumes major hunks of time. Most forum administrators lose patience and want those people who draw negative attention to not post, plus they quickly delete discussion threads that turn personal throwing out everything, good information and bad. As a retired senior computer engineer who was responsible for Internet information security for a large government organization, I can easily trace posts to find the person’s name, address, and ISP. I traced the major complainers and found that of the fifty people attacking my efforts, there were really less than a dozen unique people who were posting under different names with different email addresses. Eight of these people all are located near one of the better known suppliers of dust collection equipment, plus two more were people the president of that firm told me he wanted to fire because they were idiots and constantly giving out bad information. Meanwhile there are all kinds of people who regularly post on the various Internet woodworking forums:

   1. Most just like to share their knowledge. I know from personal experience that my students and even my own adult children are reluctant to listen to the “old salts” that spend so much time sharing war stories and have an opinion on everything unless they want an answer to a specific question then they are all “ears”.

   2. Some people like to post because they like to stir things up. These folks either get very good at couching their responses or cleverly initiate controversy in the form of innocent sounding questions.

   3. Sadly, I think the largest reason for sharing, particularly on the part of those who post constantly on a wide range of topics is money. These forums are now big business. At over $2000 a page per issue, vendors spend tens of thousands of dollars a month to get you to see their ads in the popular small shop woodworking magazines. Don’t you think these vendors are willing to spend $2000 a month for a well known poster to promote their products when our free woodworking forums often have more subscribers? The more popular small shop forums are now big business where key vendors spend large dollars to make sure their products are seen in a positive light. With my name being well known for dust collection in the woodworking industry almost every major vendor has approached me with offers to work with or for them. A number of my friends make a good portion of their incomes from this advertising. The normal approach is for the vendors to approach the more respected posters and forum moderators with guaranteed minimum monthly payments plus sales commissions.
      
      As a forum moderator and frequent poster, I was approached in the late nineties with a pretty big offer. The dust collection articles I put on my web pages stirred up incredible interest. A firm offered to pay me 3¢ for each visit to one of my web page articles that contained a link to their pages plus 5% commission on each sale that came from my pages or my posts. With a unique visitor count already in the thousands a day, I would be making $100 a day, plus a few thousand a month in commissions. All I had to do was run their unique visitor tracking software and include in my links to their web pages a special code that identified me for payment. I have spent most of my life working in the scientific world where any instance of trading on my skills our putting out information that will not pass a peer review destroys ones credibility and career. I also had experience with that vendor’s products and did not want to recommend them. I said no.
      
      I also learned there is also a very negative aspect to how many dollars these free forums impact. It takes only a few words from those we respect to seriously hurt product sales and apparently the bad things I was saying about poor dust collector and cyclone collection were hurting a few of the previously more successful advertisers. Two approached me fairly, explained how much any negative post from me hurt, and asked me to be gentler. They also complained that my early posting of test results which were accurate, just no longer applied because they had mostly due to my efforts greatly improved the performance of their blowers, dust collectors, cyclones, and filters. I agreed to back off if they stopped making illegal exaggerated advertising claims for performance levels their equipment could not possibly attain.

Kit Cyclones & Blowers

1. I don't have the expertise, time, or interest in getting into metalworking. Why don't you offer your cyclones for sale either assembled or in kit form?
   When I started this effort I was a senior engineer with a more than full time job who regularly lived with two pagers and a paging type cell phone. I am disabled with a bad leg that limits me to at most a couple of hours a day total on my feet. My medical problems forced me into an earlier than planned or desired medical retirement. That left me without the physical ability to run or manage another business, saying nothing of now being even far less able to do the work myself. Instead I have licensed my designs for others to build and helped my son and daughter cut out cyclone kits to help them earn a little extra spending money and help woodworkers uncomfortable with laying out the plan and cutting the metal themselves.

2. Why don’t you continue to make metal cyclone kits available or sell an all metal cyclone? I think that would be an incredible business and get rid of the one drawback I see with Clear Vue Cyclones using a plastic design.
   Actually the plastic used by Clear Vue Cyclones survived far better during shipping than the sheet metal used by my son and daughter who started cutting cyclone kits out of galvanized metal to help local woodworkers when they were both still in high school back in 2002. They did very well earning a little spending money. As word got out people from out of our area began ordering these cut kits. Sheet metal is hard to ship as it tears its way out of flat packs and rolling all into tight enough pieces to fit into a cylinder without over rolling creates a box that is right at the maximum size delivered by UPS and too big for either FedEx or the USPS. We found our flat packs were losing parts that broke loose and cut their way right out of the packages. Our rolled packages invariably arrived badly bent up because the large packages ended up shipping with much heavier items that destroyed our even heavier boxes and the cement forms we shipped in. When my daughter left for college, my son was not too inspired to continue that business. When my son left for school I was thankful the business was closed as I lost money off that business that helped my kids earn a little extra spending money.
   
   I got talked into licensing the manufacture of these metal kits to an Internet friend and when that business did not work out tried with a second friend. That also did not work out so I closed the kit business down completely in early 2004. Nobody now sells my cyclone design except Clear Vue Cyclones. If you hear of anyone else doing so please let me know.
   
   Although I have heard some whining that it takes some time and work to build these cyclones from galvanized steel, I also know many continue to do so as I have two or three a week emailing questions on building these units. I recommend those who have limited budgets or are convinced that they need a metal cyclone that they build one from my free plans or buy one from Ed Morgano from Clear Vue Cyclones. I cannot build one myself for the cost that Ed charges. Whether you build or buy, I do know you will be very happy with the results. Now over 7,000 people world wide use cyclones of my design that they built or bought from Clear Vue Cyclones that follow my plans. The feedback remains 100% pleased with the excellent airflow and very good dust separation.

General Site Questions

1. Why don't you just use full sized pictures so I can really see what is going on?
   If you have been following these pages for a while, you will know that I started with thumbnails that you clicked on for full sized pictures. For those of us with fast connections this worked like a champ, but for those with dialup connections, it made for a miserable experience with long waits. Many complained most strongly with a few saying it took over ten minutes to load just a single page. My goal is to share this information with as many as want. To that end I shifted to one or two color small image diagrams that show what you need to know without taking hardly any time to load at all. One person demanded I maintain two versions, one with the big pictures for him and another with the little images for those with slow connections. I told him this already takes at least two hours a day and often four or five hours. I do not get paid for any of it, and in fact, pay dearly for the overhead and traffic generated on this site. I have consistently declined sponsors because I want to maintain my impartial standing.

2. Where did Bill's plans come from?
   There are two parts to this question. First, how did I come up with this design and second, how were the plans drawn.
   
   My first cyclone had twice as big of motor as my Jet 1.5 hp DC-1100 dust collector, but felt like it only moved half the air. By nature or as my family would say, by obsession, I was totally unhappy and had to know what was going on. This of course gave me an excuse to go out and buy my own test gauges. I was wrong, that 3 hp cyclone moved less than half the air of my dust collector. I got rid of that unit and replaced it with the "best" recommended cyclone. That was a total disaster that landed me in the hospital and launched these pages, so I then built my own cyclone from the Wood Magazine plans using PVC. It worked only a tiny bit better, so I began researching to find out why. That led me to discover these cyclones were agricultural designs intended to have huge power eating internal turbulence to separate dirt and sand then blow all the light stuff out the top. This design that most small shop vendors sell as their cyclones was never made for good fine dust separation.
   
   I used Visio quite a bit at work to document information systems so used it to rough out a set of plans to fix a friend's Tempest cyclone that had a tiny blower opening. He conned me into going further and doing the same for an upgrade to the "Wood" plans that people are buying from "Wood" magazine and from Penn State Industries on-line. When I finished, it turns out I had totally redone everything on both units except the outer cylinder and even that got cut up some for a better inlet. Frustrated at redrawing for every different type of configuration, I redid them again in Microsoft Excel so it re-dimensions and redraws automatically unfortunately not to scale as it will not adjust angles or line sizes. Although all these changes reduced cyclone resistance and increased airflow by more than a third, they were still left with dismal fine dust separation, not much better than the trashcan separator lids. They still shoved almost 100% of the fine dust into my expensive filters.
   
   I then went back to the research literature on swirl tubes of which a cyclone is a special case, calculated what would provide the best fine dust separation using the smallest motor, then went to work bringing together the parts and pieces to make that happen. It took roughly six prototypes and a year’s work before sharing out my first cyclone design in early 2000. This unit pushed the separation efficiency up into the mid ninety percentile. One of my Internet woodworking friends coined the phrase "Bill's Cyclone" back in late 2000 and that's what they've been called ever since. Continued improvements now have these units moving more air with far better fine particle separation than other hobbyist cyclones.



Getting Started

1. Bill, I’m an engineer and have done a lot of research because there are a few pretty knowledgeable sounding people saying very different things than you on the Internet woodworking forums. My homework satisfied me that most of these people either don’t know what they are talking about or paid by vendors to mislead because they do not want what you say to hurt their sales and possibly get them tied up in litigation. Still, there is something I really don't understand. You say there are four major levels of dust collection and each requires different airflows. I understand that by “chip collection” you mean collecting the same chips and sawdust we would otherwise sweep up with a broom. I’ve seen lots of tables that show most of our tools only need about 350 CFM for “chip collection”. I also see other tables on your site and other professional air engineering sites that show we need to move about 800 CFM to get the air quality recommended by OSHA. I understand the need to move more than twice as much air to meet the OSHA standard compared to “chip collection” because we are collecting over a wider area and need bigger better hoods. What I do not understand is why we only need to move about 900 CFM to meet ACGIH standards that are five times tougher than OSHA standards, and only 1000 CFM to meet the medical standards already adopted in Europe that are fifty times tougher than OSHA standards. Why is it we only need to move just a little more air to meet the ACGIH and medical air quality recommendations?
   You are right. There are four major dust collection standards. "Chip collection" means picking up the chips ample to pass fire marshal inspections and comply with the National Fire Protection Association (NFPA) regulations. Chip collection can be done on most of our larger tools with only 350 CFM. The U.S. Department of Labor, Occupational Safety and Health Administration (OSHA) after nearly thirty years of debate finally set indoor air quality standards for large woodworking facilities in 1989. The large woodworking manufacturing concerns are a significant financial and political force that argued air quality standards would bankrupt their already troubled industry. These OSHA standards when issued were fifty times more lenient than recommended by EPA and medical experts. They were five times more lenient than recommended by hygienists. They also only applied to the largest woodworking concerns leaving the six out of seven full time professional woodworkers that work in small shops unprotected along with all part time and hobbyist small shop woodworkers. No oversight was proposed for vendor controls. Even so this OSHA standard was overturned in 1992 by court order before it even fully went into effect. This OSHA standard measures the average weight of dust in a cubic meter of air. OSHA allows 5 mg averaged over an eight hour period with no fifteen minutes to exceed 15 mg per cubic meter for what is called nuisance dust. Nuisance dust is considered inert and has no negative health effects other than too much clogs our airways and can lead to chronic sinus and respiratory infections. We now know that wood dust contains and carries chemicals that can be poisonous, can cause serious irritation and infection, can cause us to rapidly build up strong sensitivities with potentially deadly allergic reactions, can cause a number of diseases, and can increase our risk of cancer. We should always check a Wood Toxicity Table and wear a good respirator mask when making fine dust. With far too many workers getting ill in large commercial woodworking facilities, the American Conference of Governmental Industrial Hygienists (ACGIH®) developed a standard that allows 1 mg per cubic meter of air. Although this is five times tougher than the OSHA standards, because we can use the same hoods and only need to provide a little wider coverage area air engineers did the testing and found we only need about 13% more total airflow to meet the ACGIH standards. Likewise, the medical recommended air quality standard already adopted in Europe and now more recently adopted by the Environmental Protection Agency (EPA) only allows 0.1 mg per cubic meter of air. If you divide the allowed 5 mg by OSHA by the 0.1 mg recommended by the medical folks this is a fifty fold difference. Again, air engineer testing found we still can use the same upgraded hoods and only need to move about 25% more air, roughly 1000 CFM at our large small shop stationary tools and dustier operations to meet the medical recommendations. In short, we only need to move a little more air to ensure capturing the fine dust over a slightly larger area to meet the higher standards.

2. Ok, this is all well and fine, but I'm just getting started at woodworking and my budget priorities are my family. What should I do?
   My doctor recommends working outside as much as possible and whenever making fine dust wearing a good NIOSH approved dust mask. I think the the 3M model 7500 pictured on the left is the most affordable and best solution for most. It comes in different sizes for a proper tight fit and has removable filters that can also use the organic filters needed for many finishes, solvents and spraying operations. My wood turner friends, agressive carvers and those with beards that cause regular masks to leak recommed the powered Trend Airshield respirator pictured on the right. Never work inside your home or in a basement with airflow shared into your home. When you must work inside your garage, wear your mask for all dusty operations and use a strong fan that you can put in a doorway to clean out your work area and blow fresh air on you when you work. Because the fine dust will linger for months and get even unhealthier by building up mold and fungus, every woodworker should always thoroughly clean out your shop after every dusty activity. Use the mask and fan whenever you paint or make sawdust then keep using the mask for the up to six hours it takes until your shop is clean if you stay in your shop. Also wear a jump suit and hat when you do sanding or other work that creates fine dust. Leave them in the shop instead of tracking the dust into your vehicle and home.

3. Bill, I am also getting started, already dropped more dollars than I dare tell my wife about on my 1.5 hp Delta dust collector, and just finished getting scared to death by your web pages. I have a basement shop that shares air with my home and not even a fine filter on that dust collector. Can I fix that collector enough to get by until I can afford a cyclone?
   The only thing that will expose you and your family to more fine dust than a basement shop is a shop doing your woodworking from a room inside your home. Even a good dust mask is worthless if you are spraying dust. With your dust collector you must take any operation outside that sprays fine dust, period end of discussion. And yes, fixing your tool hoods, using larger tool ports, larger 6” ducting, and putting a fine big cartridge filter on your dust collector will all help lots, but you still will regularly have to replace your filters because dust collectors push too much dust into the filters and this dust is full of sharp particles that will push, cut and tear their way right through your fine filter especially during cleaning. You need to use an amp meter, air gauge, or expensive particle counter to know when it is time to change these filters. Commercial shops almost always use outdoor filters where they can exhaust the fine dust outdoors, because the indoor filters are more expensive and need constant replacement. It all depends upon how much fine dust you make, the surface area of your filter, and what kind of wood you use. If you use lots of the very toxic exotics like cocobolo, walnut, incense cedar, and even oak, then you need to change more often.

4. I hate you and all you are saying about fine dust. Years ago when I first began reading your posts you struck me as a fanatic to ignore and I did. Last week my doctor pulled the plug on my tools, put me on a CPAP with supplemental oxygen day and night. My x-rays show I have severe lung damage similar to fiberglass and asbestos exposure and my allergy tests show I have severe allergies to my favorite woods. Why didn't you hit me and everyone else over the heads hard enough to get my attention before this happened to me?
   I tried that back in early 2001 and got myself thrown off most of the larger woodworking forums and called just about every name from idiot to religious zealot, with a lot of lesser profane names thrown in. You have my sympathy and you are welcome to send me a personal email and I'll share all the things I've found that seem to help my similar condition. But what I want from you is your also helping to rattle the cages of the far too many who are certain we are the exception and nothing will ever happen to them like us. As far as I am concerned most small shop professionals and hobbyists are driving without brakes. A crash is inevitable, just a matter of when and how bad.

5. What do I really need for safe dust collection?
   Wood dust is much like smoking. Different people are affected differently over a long period of time. The immediate risk from airborne wood dust is getting constantly clogged up. This causes most to develop infections that become chronic if you keep taking in too much airborne dust. Most airborne dust is made up of particles 30 microns and smaller The next most serious concerns with taking in too much wood dust comes from the chemicals in wood and carried on wood. Some of these chemicals are poisons, cause permanent nerve damage, cause irritation which leads to infections, are sensitizing agents that increase or risk of having a potentially fatal allergic reaction (the problem that nearly got me), can increase our risk of cancer, can cause a number of diseases, and the fine invisible particles cause permanent loss of function that increases over time depending upon exposure. Please see my Medical Risks web pages for more detail. Unless you have an immediate toxic or allergic reaction the odds are it will take ten or more years of regular small shop dust exposures before you develop enough symptoms to affect the quality of your life. Being foolish and badly contaminating your home with woods known to be toxic can cause serious problems in a few days. Since our bodies have a very difficult time getting rid of this dust, the more we take in and longer the exposure, the faster we build up allergic reactions and develop dust related health problems. To pass the medical air quality inspections in my state, you need to capture these fine particles at their source before they become airborne.
   
   The air engineering information I found shows that the older cubic feet per minute (CFM) tables were designed to collect sawdust and chips now known as “chip collection”. The newer tables show we must fix our tool hoods and provide a much higher CFM our tools to collect the fine dust. The issue with hoods is simple. Our blades, bits and cutters often eject dusty air streams at over 100 miles an hour. Even a very powerful dust collection system rarely moves air at over 60 miles an hour. Unless our hoods block and contain these fast moving air streams we make so much fine dust that we quickly end up with badly contaminated shop air. In addition to upgraded hoods we also must move enough air to make up for our tools and hoods not really fully containing the fine dust. To meet OSHA air quality standards air engineers found we need to move about 800 CFM at our larger tools and closer to 1000 CFM to meet the fifty times tougher medical and EPA air quality standards now already adopted in Europe.
   
   Fixing our tool hoods and providing enough airflow is still not enough. We also need enough airspeed in our pipes to ensure they do not clog and we need to get rid of the fine dust. We must keep wood dust moving without clogs, plugging, or building up dangerous dust piles inside the ducting. We have tables and years of testing that show most of us are fine with systems designed to ensure about 4000 feet per minute (FPM) airspeed in our vertical ducting runs.
   
   Finally, getting rid of the fine dust is not so easy. Fine dust rapidly clogs fine filters killing the airflow we need for good collection. Cleaning our fine filters is a pain and rapidly ruins these expensive filters, so most commercial shops use a cyclone to separate off the heavier sawdust and chips then blow the fine dust away into the outside air with no filters. Those who filter need to replace fine filters after about 20 full bins of chips which is roughly quarterly or about every 500 hours of use. We need a manometer to know when to change our filters. These only cost about $16 (search for Radon store manometer) to buy or you can easily make one from a clear tube looped and filled with colored water. When the blower is off the water level is at zero. Put a ruler on that tube with the end (zero point) at that water level when the blower is off. When the blower turns on if we have more than 1” of pressure then we have too little filter area for our air flow so need a bigger filter. When the filter goes over 2.5” it is time to clean.

6. I've been watching these dust collection discussions on the Internet forums for a while, and you are the first to make a big deal about FPM. What is this and why?
   Feet per minute (FPM) is the speed of the air in your ducts and is what holds the dust in the air instead of letting it fall and get stuck, mostly in our vertical runs. Likewise, airspeed and air volume combine to determine what sized particles we will move and over what total area. After many years of testing and experience, air engineers developed and refined their material handling tables to show how much airspeed and volume are needed to collect and transport various stuff. Sawdust and wood chips require up to 4500 FPM for collection and transport, but with the mostly smaller chips in small shop woodworking we can get by with less volume and speed. If you make nothing but finer sawdust and chips, meaning no planer, router, shaper, etc. you can get by with as little as 3000 FPM in horizontal runs and 3700 FPM in vertical runs. Most make larger chips, so air engineers build our dust collection systems with about 4000 FPM airspeed to ensure we do not get clogging in our vertical runs. Going well beyond that is easy, but begins to cost money buying a bigger blower and paying for more power than you need.

7. You say you built your cyclones and two different blower combinations to move at least 800 CFM at your larger machines with an air speed inside the ducts of at least 4000 FPM. I just finished reading a site put up by a professional engineering firm and they say I only need 450 CFM at my machines. Why can't you guys be consistent? Who do I trust?
   Sadly, we had an old standard that worked well for “chip collection” which means picking up chips and sawdust you would sweep up with a broom and dustpan. To get the really fine under 30 micron sized particles right at their source, you need to move considerably more air. I don't know which site you went to that gave you that information, but most of the professional sites were upgraded in early 2002 after my friends and I started a major Internet education campaign to get some of the bad information cleaned up. Those old “chip collection” numbers of only 350 to 450 CFM are dead wrong for getting the really fine dust. Check the CFM Requirements Tables above then the ducting pages. On the first you will see real CFM requirements, not dated information or something put out by a firm trying to sell undersized or dated equipment.

8. Do you honestly think that it's worth putting in 6" ducting and hoses right to your larger tools and installing a cyclone?
   Yes, I do! Please go read my Dust Collection Introduction web page.

9. Just like you I am a long time woodworker and lately have been more and more bothered by the dust. I know you are right and I am willing to start making changes today. What do you recommend for my priorities?

   1. Get yourself in to your doctor and make sure you are not developing a serious problem.

   2. Start with the same steps just mentioned for a beginner.

   3. Finally upgrade your dust collection system with good dust collection hoods at each machine to catch and control the fine dust at its source, ample ducting to move that dirty air, and an appropriate system for your needs. For sure build yourself a good sanding table that you use whenever hand sanding or using your random orbit sanders. What my doctor told me was to work outside with a good dust mask whenever possible, use a good trashcan separator and exhaust the air outside if it is safe and legal, or buy a good commercial dust collector or a good cyclone with high quality NIOSH 0.2 micron approved cartridge filters. My own experience found there were no good cyclones for indoor use, so if you don’t choose to go with my cyclone design at least send the dusty air outside.

10. Perhaps my intuitive sense of physics is wrong, but I don't understand why more airflow is required to pick up finer dust. I agree that fine wood dust is like asbestos in that it is near invisible and can be deadly to our health over a decade or three. This finer dust stays suspended in the air for hours even with no air movement. If the air near the dust generation point and the dust we can see is moving into the hose, shouldn't the fine dust go too? My intuitive sense of how this works is that the finer the particle is, the easier it is to move. Everyone knows that a fraction of the air movement needed to pick up heavier chips will easily move this fine dust. It seems to me that if the airflow is enough to pick up the big stuff, and keep it from clogging the pipe, it ought to be enough to pick up the little stuff and keep it from clogging the pipe as well. If there is a good answer to why my intuition is wrong, I want to know it. The answer that will convince me you are right is one that is based on the physics of the situation, not "the table says so." I don't need a super-detailed physics lesson. In fact, I'd settle for a good hand-waving (no pun intended) argument about why my intuition is wrong.
    You are correct this at first does not make sense, because these fine particles get moved by so little air movement. Considerable testing by air engineers and over fifteen years of experience proves we need to move the additional air but does not explain why.
    
    To understand why, let’s start with “chip collection”. For good chip collection we need tools that are designed to blast all the heavier sawdust and chips from our blades, bits, cutters, belts, sandpaper, etc. in a specific direction. Our tools then use a hood to capture that fast flying and easily visible stuff and direct it to our collection port that ties to our ducting. We need enough airspeed to pull in that dust and enough airspeed to keep it from settling into dangerous piles in our ducting pipes. We also need to move enough air volume to cover the whole area where the chips are being drawn from. Air engineers long ago did considerable testing on most stationary woodworking tools to develop the hood designs we need and define how much airspeed and air volume were needed at each tool. Airspeed to keep the ducting clear turned out to be more than needed at each machine, so most air engineers round that needed duct airspeed up from about 3800 feet per minute to 4000 feet per minute as an ideal speed. Most of the smaller commercial stationary tools that are identical to larger hobbyist tools get excellent “chip collection” with an air volume of between 350 to 450 cubic feet per minute. Lots of testing confirmed those values. The firms that sell dust collection components to air engineers developed excellent “chip collection” airflow requirement tables sharing how much air volume is needed at each tool for good chip collection.
    
    In 1989 when OSHA imposed five times tougher airborne dust limits, the dust collection equipment suppliers had to go back to work. Almost all large commercial shops already blew the fine dust away outside, so getting the fine dust levels down meant going after the fine airborne “fugitive” dust that escaped collection and being sent away outside. They found that 50 feet per minute airspeed was ample to capture this fine airborne dust and overcome normal room air currents. As proven by a few of the newer tools built from the ground up with good fine dust collection built in, they were absolutely right, a large shop vacuum does a great job on fine dust collection on these specially built tools. In our real world, most of us buy tools with older designs that at most provide “chip collection” with no fine dust collection built in. They are not optimized to control or capture fine dust. Air engineers found that most small commercial tools that are identical to our larger hobbyist tools had serious problems with their designs allowing our blades, bits, belts, cutters, sandpaper, motors, etc. to launch the fine dust all over before it could be collected. It was near impossible to stay under government airborne dust limits once that dust escaped, so they had to capture it as it was made. Repair required even better hoods and in many cases extensive tool modifications to keep that fine dust protected and controlled until it could be collected. Even with these better hoods, they still had a problem with our tools blowing too much of the fine dust away before it could be collected.
    
    Their solution that proved workable requires both better hoods and building a fairly good sized “bubble” of air around the dusty portions of our tools to pull that air back before it gets launched into our room air currents. Their testing found the airspeeds that worked well for chip collection also did a great job for fine dust collection, but they had to move just over double the air volume to build a big enough “bubble” to ensure collecting this finest dust as it was made.
    
    To answer why we need to move so much more air to build this “bubble”, we need to understand the basic difference between blown and sucked air. When we blow we create a directed stream of air. That stream will stay together for a fairly long distance until slowed by friction. Conversely, when we suck, we end up creating a low-pressure area around an opening that gathers equally pretty much from all directions. Most of us already know this from working with our shop vacuums. When we put them on blow they will stir the air all over our shops, yet when sucking we can only pickup right next to our collection hose. The math shows airspeed falls off at about the same as the surface area of a sphere expands which is 4 times Pi times the square of the distance away. Our 4000 foot per minute duct airspeed that moves a real 349 CFM in a 4" diameter duct drops to well under our needed 50 feet per minute airspeed just 6” away from the center of our hose. We end up having to use much better hoods and move lots more air or those particles will get blown away by room air currents before they can be collected.
    
    The other issue you raise is a serious concern. The 2.5-micron and smaller diameter particles that cause the most long term health problems are near invisible. As a result, shops like mine that used finer filters that gathered in most of the easily visible dust and kept my tools looking clean may well generate a false sense of security because most hobbyist filters provide little to no filtering of this finest near invisible dust. So, yes you are right, "…visible dust collection performance is not a reliable indicator of invisible dust collection." You are also correct that this lightest dust is even more easily sucked up, but unless you are providing ample collection and then either blowing it away outside or filtering it off, it will just build in our shops to dangerously unhealthy levels. With the airflow from our tools pushing this “fugitive” dust airborne again and again, it poses a serious long term danger to most small shop woodworkers and all close to us. About the only way to find out if you have this problem short of expensive professional testing is to use a laser pointer and see if lots of fine dust is escaping collection or through your filters.



Venting Outside

1. Bill, I bought a brand X cyclone that came with a fine cartridge filter. Although I read your web pages and realized that you said to make or buy your much better cyclone design when using fine filters or vent outside, I got talked into venting inside by my vendor and buying their expensive fine filter. I was happy as a pig until one of my friends bought that new Dylos air quality meter and brought it over to my home. He scared me to death. I regularly work with cocobolo, teak, paduk, and a whole bunch of other woods that are bad news on your Wood Toxicity Table. That meter showed doubly bad news. Just turning on my cyclone without doing any woodworking pushed that meter far over the maximum most dangerous reading. Like most I have a garage bas4ed shop with a sealed door between the garage and home with no shared airflow. Taking the meter in my home showed an airborne dust level high enough that my family and I should live in NIOSH approved respirator masks. So this leaves me with two questions. First, why didn’t you tell me that “best” magazine rated cyclone was a piece of junk? And second, what do I do now to fix this mess?
   Your situation is just like mine was with your fortunately not yet having any serious medical problems. It is no secret that my “best” magazine rated cyclone with vendor designed and supplied ducting and upgraded fine filter landed me in the hospital. Likewise, my home three months later still tested with dangerously high airborne dust levels.
   
   My landing in the hospital with the magazine recommended “best” dust collection system available inspired me figure out what went wrong and how to make repair. My respiratory doctor convinced me so many other woodworkers and family members of small shop woodworkers were having problems I needed to share. I share on these pages, but frankly got tired of getting law suit threats. My attorney told me to remove the name of that “best” vendor that landed me in the hospital which I have done.
   
   Meanwhile, huge numbers of woodworkers continue to trust our small shop vendor community to protect our health. That is misplaced trust because these folks sell “chip collectors” with finer filters. The dust collector blower industry is mature. You can easily compute the low and high resistance levels of your shop, look up the required CFM for good dust collection at your stationary tools, and then use a fan table to see how big of a blower housing, blower impeller, and blower motor you need. Because most small shop vendors have blowers that are far less efficient, a good commercial fan table like those shared by Cincinnati Fan for their aluminum and steel pressure blowers will give the upper end performance you can expect from small shop blowers. My testing found only WMH Tools (Jet, Powermatic and Wilton) and Delta sold blowers that were close to industrial standards. The worst cheapest imports I tested provided half the airflows we would get from the same size and horsepower blower. Regardless, for good fine dust collection you need 1000 CFM at your larger tools.
   
   What this means for dust collectors is at this 1000 CFM airflow and typical shop resistance levels we need at least a 13” impeller powered by a 3 hp or larger motor to move enough air for good fine dust collection. Even huge dust collector fine filters quickly plug at this airflow, so the best solution is to put all dust collectors outside and use the far less expensive more open filters that freely pass the 30-micron and smaller airborne particles. Venting outside requires makeup air that should be at least twice the diameter as the outlet duct. This makeup air keeps from sucking deadly carbon monoxide backward through our flues and vents.
   
   For cyclones we have a little different story. There is one small shop cyclone that works so poorly even the magazines recommend against its purchase. As of early 2008 every other small shop vendor except Clear Vue Cyclones is selling cyclones of my earlier design. I gave up on that earlier design because even with my changes that double airflow it still separated about the same as a $25 trashcan separator lid. That is why I came up with my more current cyclone design that only Clear Vue Cyclones is authorized to sell. This newer cyclone design with over five times better fine dust separation and over one third more efficient airflow is the only cyclone I recommend venting indoors through fine filters. All other cyclones should have the filter tossed and vented outside also with make up air to avoid the carbon monoxide poisoning problems.
   
   Venting inside can be done with anything if you are get a good quality (expensive commercial) filter, regularly clean that filter, and replace it when it gets shot. In eight years of testing only the Donaldson-Torit, Farr, and Wynn Environmental fine filters actually worked as advertized. All other small shop filters freely passed ten to twenty times larger particles than the advertised claimed filtering level. Please see my filter discussions for more than you ever wanted to know. If you are going to vent inside without using my cyclone, I strongly recommend you get and regularly use a good air quality meter. When you mess up and make a lot of airborne dust or your filters need replaced, the meter will tell you when to replace filters. Alternatively you can make or buy a manometer and carefully track your pressure drop after cleaning. When the pressure drop is too much then you need to replace the filters. Sadly, without a test gage it is tough to say just when it its time to replace the filters.
   
   What I did to cleanup the badly contaminated air in my home was to open all up with a huge whole house fan running, vacuum all thoroughly with a strong commercial vacuum that vented outdoors, and then install a large commercial Honeywell hospital air cleaner. Adding really fine filters to my heating system is something my HVAC engineer friend said not to do. These really fine filters block the airflow we need for good ventilation plus kill the airflow needed to keep all cool enough. Without enough airflow our heaters and fan motors quickly overheat which can be expensive.
   
   Today with what I know I would instead make my own air cleaners. For my shop I would use one of the larger Fantech 8” inline 450 CFM+ fans with the whisper quiet impeller coupled to one of the new Clarke MERV-15 rated microfiber fine large filters that you can buy from Wynn Environmental. Seal the bottom, insert the fan inlet into the filter so it sucks through the filter and blows outward. Depending upon how tight the fit you might need to seal the fan in place with polyurethane caulk. Wire it up to a standard 110 cord and let if go. This setup will change out the air in my three car garage based shop almost exactly six times an hour. The six airflow changes an hour is the target you want also for your home. In my case I need to use a few of these. I instead bought a surplus Honeywell hospital air cleaner. It moves lots of air, but is not compatible with me because it makes too much noise. use a digital timer to have it turn off at about bedtime. These draw about the same power as a 100W light bulb and do a pretty good job of moving lots of air. Your target should be at least six air changes an hour. In my home I need two of these.

2. Bill, you really confused me. I built a Bill Pentz cyclone design and am powering it with a Leeson motor and impeller I bought from Clear Vue Cyclones, plus am using the more expensive all poly filters you recommended from Wynn Environmental. I read on your new web pages, which I appreciate the rewrite that you always recommend venting outside whenever possible and only recommend venting inside if we use your cyclone design and through fine filters. Should I blow the air outside or should I vent through my fine filters? I live in the Southwest where the freezing winter and nightime temperature couple with boiling summer temperatures to have me almost always either heating or air conditioning my shop. Do I vent inside through these filters or outside?
   I get beat up over this question a lot. I guess the easy way to answer this question is to tell you what I told one of my very good friends who has one of my cyclones. I said make a diverter valve and always vent outside when the weather is mild and when too hot or cold vent through his filters. I also made him go buy an air quality meter so he can see when he has a fine airborne dust problem.
   
   The longer answer is more technical. Yes, I only recommend using my cyclone design if you are going to vent inside through fine filters. For all other cyclones I would like to see them vented outside with no filters and makeup air as needed. Even with my cyclone I prefer to see it vented outside as that is the only way to ensure that whatever dust you miss during collection ends up getting blown away instead of trapped inside. At the same time, the whole purpose of my cyclone design is to provide a cyclone that separates well enough to vent indoors.
   
   My reasons for wanting all other cyclones only vented outside are undersized blowers, undersized filters, and too open filters. Not one small shop cyclone filter I tested provided one tenth the fine dust filtering advertised. The air tables are clear we need at least 3.5 hp to power a small shop cyclone and move 1000 CFM against typical resistance. Most of these cyclones use 3 hp and smaller motors so start already in the hole meaning they are going to miss collecting some of the fine dust even with well upgraded hoods. We make so much dust with our woodworking, the little dust that escapes collection will rapidly build to dangerously high levels. I want to see that dust blown away outside instead of building up inside. Now add undersized filters and what happens is the filters quickly plug further killing the already too little airflow and making for a constant need for cleaning. Cleaning quickly wears out our expensive fine filters. Swapping these undersized open filters only helps a bit because these cyclones separate so poorly they far more quickly load up our finer filters soon making them history. In fact the fairly open 10-micron typical small shop filters will last about five years but the fine filters least less than one quarter of full time woodworking.
   
   My cyclone design from my plans or provided by Clear Vue Cyclones was engineered to vent indoors through fine filters. It has a five times better fine dust separation, plus I configure these with much better quality filters that are sized at about 600 square feet versus the hobbyist cyclones at around 100 square feet of filter area. This combination will let a good commercial set of fine filters last in most small shops five years of nearly full time or ten years of part time woodworking. At the same time, I know that even my cyclone having high airflow and our upgrading our hoods, downdraft table, etc. we are still going to miss a certain amount of this fine dust. With a small thimbleful enough to fail the more sensitive air quality tests, I would still like to see this fine dust sent away outside. At the same time I also know that with the airflows in my cyclone design and the provided filtering we are going to get a lot of air movement and the air that goes through the cyclone will be cleaned. Is this good enough> That totally depends upon how well you made your hoods, downdraft table etc. and how you work. I think you can vent inside just fine in most cases, but would still like you to have an air quality gauge going so you can tell when you are developing a problem instead of ending up in the hospital like I did. The problem is the worst of this dust is invisible and unless you have a keen nose to smell this stuff, you could also easily be blindsided by the more toxic woods.



Maintenance

1. I'd like to know about what is required to maintain my dust collector or cyclone?
   Other than normal tool maintenance meaning keeping your unit clean, ensuring the cord does not become frayed, etc., there are only a few things you need to do to maintain your blower. I think all DC and Cyclone blower impellers and blowers should be checked at least quarterly and cleaned of any dust and pitch buildup. Additionally, you need to regularly clean your filters and if you bought washable filters you need to occasionally wash your filters. See the Filter FAQs for more details on how to determine when to clean and how to do that cleaning.

2. When and how do I clean out my clear flex pipe or other tubing?
   I’ve never needed to clean my clear flex duct because the heavier planer chips etc. keep it well cleaned. If you are having a problem due to wet wood, high sap, etc. you can clean most flex with soap and water. It that does not work, test whatever solvent before using it on your flex hose because some solvents and ruin and discolor this hose.
   



Blowers and Impellers




1. I'd like to know, with data, how a DC performs in real-life situations. Hook up a DC to varying lengths of different kinds of tubing (PVC, metal, flexible) with different types of connectors (T's, wyes, straight, etc.) and test specific parameters such as CFM.
   Although many don’t quite understand, the whole idea of having a static calculator is to let us get a good working estimate of how much resistance we will have in a particular ducting setup without having to test each and every different type of setup. Once we get a good estimate of that resistance we can look at a fan table or fan curve and get a really close idea of how our DC will perform. There are a few surprises with small hoods, undersized ports, poorly made DCs, etc., but not that many. You can pretty consistently look at a fan table for your sized impeller at whatever resistance you want to challenge it with, and see what kind of airflow is expected. . Most of these questions and how to do the estimating are pretty well answered on my Ducting and Static Calculator pages.

2. I've been looking for a blower for ages and still can't find a 1.5 to 3 HP motor blower combination anywhere. What should I do?
   Everyone else is also looking for the same single phase 2 to 5 HP motor-blowers. I've seen used ones sell on EBAY for far more than new ones cost. I think the Jet and Delta 1.5 hp and larger units are the most cost-effective solutions for a small shop dust collector for placing outside. The bigger 3 hp units from these same vendors are better for a large shop dust collector. For a cyclone, you really need a bigger than stock blower impeller, so buying one of these is tough. You can buy a huge blower and put on a smaller motor, or build your own. In either case you still need to carefully monitor the motor amperage to ensure the motor does not get over stressed.

3. You have me so confused I don't know which end is up. Are you saying I need to get a blower to run 800 CFM at every tool in my shop?
   Absolutely not and for sure yes! I have been beaten up by almost every hobbyist dust collection parts supplier because their ducting design programs size each ducting down drop to exactly match the specific needs or at least port size for each machine. The mains in turn taper to exactly support the needed airflow to match the branches. This creates very impressive ducting layouts in hobbyist shops and works terribly. The problem is we use small blowers that can only power collection for one machine at a time. We size our blowers to overcome the resistance of our longest run and provide ample airflow for our highest need machine. Unless you have oversized commercial tools this highest need for most hobbyists is 800 CFM as carefully established by testing and made available on CFM requirements tables similar to the one AAF lets me share. Because air at typical dust collection pressures is more like water and will barely compress at all, any restriction, constriction, small pipe, etc. will kill the total volume unless you use a significantly oversized blower. In a commercial ducting system this does not matter since all ducting runs are open at once and they use huge blowers. But in a hobbyist system with just one run open at a time and a small blower, the result is a mess. Yes we get good collection at the specific machine with a smaller down drop, but when the reduced air volume created by that smaller pipe hits the main, the airspeed drops far below what we need to prevent plugging and build up of dust piles. Dust piles pose a serious fire hazard and ruin motor bearings, impellers, and filters when they break loose and go slamming around. To keep the airflow ample in the mains of a hobbyist system that only has one run open at a time, we must use the same sized down drops as our mains. Just laugh when you hear about the 800 CFM stealing your drill, small tools, pets, etc.

4. Ok, so I don't need a full six inch pipe at all tools, but most of my tools have 4" exhaust ports and you said that necking down to below 5" will cause the airflow to slow so much I'll get clogging in my main ducting runs. What do I do?
   You do need 6” down drops off your 6” mains. Necking down to more than 1” smaller diameter pipe can cause the mains to clog. Nothing says you can't go with 6" right to all your machines. More airflow hurts nothing. To do so, you will need to replace the 4" ports with 6" ports. You often also have to change internal machine ducting. What I do is put the blast gate as close to my ceiling mounted 6" main as possible, then come down with 6" into a wye splitter. For tools requiring two ports or needing less than 800 CFM I split the 6” into 5” and 3.5" hoses. The larger flex hose connects to the machine port. Super magnets hold the spare hose(s) to the tool to help with additional collection. With all being open with that single gate that assures the needed airflow.

5. Ok, what do the airfoil impellers look like and where do I buy one?
   Airfoil impellers move far more air for the same horsepower with less noise. For those that care a typical material handling impeller generates at best about 45% efficiency versus roughly 80% efficiency for an airfoil. Airfoil impellers are designed to work with open systems where they will have a constant supply of air and not too much resistance. With too much resistance or too little air, the airfoil blades stall creating destructive vibrations and other serious problems. If you don't use very efficient ducting that is 6" or larger, open large filters with minimum back pressure, and keep one blast gate open all the time, an airfoil is not a good solution for you.
   
   I found four industrial suppliers carry airfoil impellers. Chicago Fan, Cincinnati Fan, and Continental Fan responded with quotes. Each wanted over $250 for quantity one plus a hefty shipping and handling charge. Continental also quoted a price of $140 plus shipping and handling for their plastic impeller. Sheldon's Engineering worked with me to design a little better airfoil impeller that would not stall so easily and offers it to hobbyist woodworkers at a very attractive price, but they changed ownership and these are no longer available. I purchased both their normal and larger airfoils and found they have incredible airflow and the stalling does not become a problem until the filter gets dirty. I was uncomfortable with hearing the stalling chatter that ruins motor bearings when it was time to clean the filters so I also gave up on the airfoils and went to a material handling impeller. I now buy my material handling impellers from Clear Vue Cyclones. Even after carefully plumbing my shop to keep the total resistance below 7” including ducting, cyclone, and filters I still had problems. Most cannot do keep their resistance this low, so airfoil impellers will not work for them.

   The WoodSucker used what is perhaps a better designed impeller for general cyclone use if the impeller can be put on the clean side of our filters. Their site which no longer exists because they went out of business showed using a large caged backward inclined (BI) impeller. At about 70%, it is next to the airfoil in efficiency, but does not have the stalling problems or sensitivity to material hits. Its design provides the suction needed to handle large single person woodshops. Larry Adcock, who designed that cyclone and impeller, said he does not want to sell these impellers except with full cyclones as there are just too many concerns and safety issues. The reports I've received from owners of these units are they love this system but regularly need to inspect and clean their caged impellers because unlike material handling impellers they end up collecting strings and long shavings that can throw the impeller out of balance.

6. I want a bigger impeller for my 1.5 HP Jet dust collector blower that I am using to power a Wood Design cyclone. I understand that the upgrade will help quite a bit. I have a welder, should I just weld tabs on my current impeller or buy a bigger one? Where?
   Not every blower can be upgraded as not all have ample power or big enough blower housing. Be careful that you buy an impeller that is compatible with the size blower housing, motor shaft size and direction of rotation for your blower. The Jet impellers only work when turning counter clockwise when looking at the blade side of the impeller with the motor behind. Adding on to my own impeller was more of a welding challenge than I could do. A few of us have ordered the 12" diameter DC-1200 for our Jet DC-1100s that power cyclones. The part number for my 12" was AB411059 and AB430006. I was told the second part number was incorrect, but is what my dealer used to order my larger impeller. I later found that buying directly from Jet Customer service was less expensive and easier because you only need to tell them you need a replacement for your DC-1200. My cost in 2002 was under $70 including shipping. That impeller for me was a direct fit with no problems at all. Each of the Jet DC-1100 and DC-1200 model impellers are held on with a four-bolt arbor hub that attaches to the motor shaft. To upgrade my DC-1100 to the DC-1200 impeller, I only had to unbolt the existing hub then re-bolt it onto the new impeller. I understand Jet has now changed these impellers, so you would need to do as I did when upgrading my other unit to use the bigger Jet DC-1900 14" impeller. That unit had to go to a machine shop and for about $80 came back with a fit for my larger motor. The machine shop cautioned me to use Lock-tite on the set screws and arbor screws. Another huge help with that cyclone is to add a neutral vane (see my blower modification instructions listed on the cyclone home page).

7. My concern is the offset of the impeller in the housing, I know it is not centered, but where does it go?
   It depends upon the type of impeller. I measured my Jet and it is centered, but in the center of an expanding spiral also known as a volute. My plan for making a blower using an airfoil impeller leaves 1/8" clearance between the impeller and the edge of the outlet. My Cincinnati blower is also centered in a spiral with a clearance of about 1.3" from the closest point, sometimes known as a gore point where the outlet straight meets the spiral. Blowers use a tangential air outlet. Although I used to recommend making your own impeller, too many had them explode and with more than twenty tons of force, this is not safe or pleasant. I used to recommend Glenn's site in my links page for information on making your own impeller, but he finally pulled down that page after too many disaster. I had enough experience with a few professionally made impellers failing that I now strongly recommend buying a professionally made and balanced impeller. For more information on making and balancing your own impeller there is an inexpensive book on Making Your Own Blower by Gingery that many have told me gives good information. As a rule of thumb, the airfoils go right next to the point in the blower housing while material movement impellers should go no closer than their diameter divided by ten to the impeller side or you get a siren and can have material jams. In terms of noise, you are better off with material movement impellers to make that spacing as much as 50% more.

8. I've been thinking and wondered if I built a cyclone in my shop/garage that is attached to my home if we could also use it for a central house vacuum?
   The answer is sadly no. A good central house vacuum needs 90 to 125 inches of pressure to deep clean carpets and drive the 2" ducts. A 2 hp standard dust collector will be hard pressed to generate more than about 12 inches of water pressure, leaving it far too under powered to serve as a house vacuum. Many do make cyclones to work with their existing home vacuum systems to save the trouble of emptying these units. I found that using a 9” diameter cyclone in my spreadsheet creates an excellent cyclone separator for our home vacuum system.



Motors

1. Why is it that identical looking motors on the various dust collectors and cyclones that turn the same sized impellers have such different horsepower ratings? Is there a way I can figure out the real horsepower of these motors?
   Without pulling any punches, the problem is our hobbyist vendors are in a war for our dollars and too many of these firms just plain cheat making motor horsepower claims that go beyond ridiculous. It used to be that you could use a couple of simple formulas based upon the amperage draw to compute horsepower:
   
   Simply multiply the amperage from the motor plate times the voltage to get watts, then divide the results by 746 to get horsepower.
   
   For example the Leeson Motor I recommend is a 220 volt motor that draws 20.8 amps when running at maximum load. Multiplying voltage times amperage gives 4576 watts. Divide that by 746 and we end up with that 6.14 horsepower for that motor.
   
   Leeson is one of the most respected electric motor makers in the U.S. and they rate that motor at a full 5 hp, not more. They do so because every motor has losses in friction, electronics, efficiency, etc. and they want their customers to know that buying that motor will consistently deliver its rated horsepower.
   
   Unfortunately, this is the exception rather than the rule. It turns out that with no oversight, hobbyist vendors can measure not running amperage, but instead startup amperage. That startup amperage can easily go 4 times higher than running amperage. This is how my shop vacuum that runs just fine on a 15 amp 110 volt circuit manages to get a vendor rating of 6.5 hp when the reality is this is barely over a 1 hp motor.

2. I really don't understand why people keep bashing import motors. What is the difference and are there any standards?
   I'm not a motor expert by any stretch and three decades since I studied them. At the same time I have been doing some homework and the difference between a class A and a class F includes:

   1. Thermal protection installed.

   2. Winding insulation that will take a higher temperature and operate in warmer environments.

   3. A good quality set of capacitors.

   4. Generally a magnetic or better quality centrifugal cutout to disengage the start capacitor.

   5. Often bigger and more carefully machined and permanently lubricated bearings that will let you run the motor at any angle, including the vertical that we often use for cyclones.

   6. Generally a better cooling fan, often with a totally enclosed fan cooled (TEFC) that can better handle dust exposure.

   7. Often a better duty cycle getting rated to run 100% of the time instead of less.

   8. Generally a magnetic holding and a series overload protection circuit to protect against startup and over loading problems.

   9. Generally the stator is dipped in insulating varnish and baked before assembly keeping the coils from vibrating and shorting.

   10. Suppose that's why I bought a Class F Baldor the last time I needed a tool replacement motor. Leeson was my second choice. Both are expensive, but I've found that motor and pump shops often have discounted new or near new quality motors at discounts from making equipment trades.

   
   
   

   My motor expert, Forrest Addy, suggested doing a few things to help an inexpensive motor:

   1. Replace the capacitors with good quality American made capacitors as they are inexpensive and good protection.

   2. Disassemble a new motor, check with a fingernail to see if the stator windings are "painted" together. If not, take it to a motor shop to have it dipped and baked.

   3. For the electrically inclined put a 1K bleeder resistor across the cap to drain the charge off rapidly and improve reliability when starting in rapid sequence if your motor is going to be turned on and off frequently.

   4. And again for the electrically inclined add a thermal cutout to the motor case to protect against over heating.

   5. Finally, with all that just about any motor will work for you fine as long as it is sized and rated so you don't abuse it or beat it up by turning it off and on too often.



Dust Collectors

1. What dust collector do you recommend?
   I don't recommend a dust collector unless you can vent it outside. I bought a Jet DC-1100 similar to the one Dizzy recommended and liked it for my small shop with almost no ducting. With just a single short smooth walled flex hose it and the similar sized Delta 1.5 hp dust collector each have plenty of power for my large planer and my drum sander. I would suggest the Jet DC-1200 or bigger Delta for those who use ducting or have a bigger shop. It takes a 3 hp dust collector to power a cyclone in average shops with installed ducting. To answer your question, if you can't make or buy a cyclone then seriously consider making your own blower or using the Jet DC-1900 dust collector placed outside. If you need to return the air to your shop, you either need a commercial certified dust collector like the Felder units or a cyclone with fine filters and a big motor and blower to power this unit.

2. I'm impressed by the new Jet and PSI cartridge filter units that mount on an existing dust collector. What do you think of these units?
   Jet claims their cartridge uses a 2 micron filter and I believe them. I recommend a 0.5 micron or better filter as that will better protect your health because the most dangerous fine dust is 2.5-microns and smaller in size. I frankly don't believe some of the imports that claim a 1 micron filter simply based on my experience with their bags not giving me a fraction of the filtering they claimed for them until so caked with dust they barely passed air. Although this may be where we are headed, until I see those finer filters certified by an approved independent testing lab and their providing some protection against the finest unhealthiest dust, I still say either put your dust collector outside or vent your cyclone outside.

3. Would the Jet Canister Upgrade Kit and the 1.5 hp 1100 CFM Jet DC-1100 be adequate for a small DC system if I am not willing to build or buy a cyclone?
   Your existing Jet DC-1100 as is makes an excellent “chip collection” system unless put outside with no air returned to your shop. This unit and the equivalent Delta 1.5 hp dust collector almost always place first in the various magazine tests because they are very well made. Unfortunately, neither when challenged with much ducting or a dirty filter moves ample air for good fine dust collection. If you put them outside with no air return, these two dust collectors are the only 1.5 hp units available that come close to providing good fine dust collection. When they are put outside there is no need to upgrade filters.

4. I've thought about just bagging the upgrade to the canister, selling my Jet DC-1100 1.5 hp dust collector and getting a 2 hp WoodSucker Cyclone. Unfortunately, I've only have one single 220 volt outlet and I think getting another would require more electrical work than I can afford now. Do you have a better alternative?
   I had exactly the same problem. I built my home with my shop in a separate building and its own large breaker panel able to run my various 240V tools. I bought a new home with a huge garage planning on making that my new shop, but only had a single 240V outlet in the garage. With my home electrical box full and the amount of power my house pulls, my electric company says to add more power I would have to change the wiring in our underground service connection. Doing so would be prohibitively expensive, so I lived with a single 220V massive extension cord that I moved between tools and used 110 volt dust collection with finer filters. After getting ill to continue woodworking I was forced into buying a 240V dust collection system. I finally had to bite the bullet and pay to upgrade the power coming in and add a bigger sub-panel in my garage. You may well be forced to do something similar if you cannot upgrade your main service amply to add a sub panel. You might have to do as I did for a while which was put my 1.5 hp Jet (or Delta) collector outside where the fine dust just blows away.

5. I have a new supposedly 2 horsepower dust collector that has a 11.5" diameter impeller. All the forums say this is really only a 1.5 horsepower motor and the bags need replaced. In looking at your plan, I can build your cyclone for less than the cost to buy one fine filter bag. I found a local truck depot that will give me used 1-micron large filters that clean up like new. My shop is a standard 2 car garage with 12" planer, 10" table saw, 16" drum sander, 8" joiner, lathe, and all the other normal tools. I have installed 37 feet of 4" ducting and each of my machines hooked up with a blast gate and a no more than 3 foot length of flex hose. The longest run is 14' to my joiner with two 90-degree bends. Can I use this blower to power that cyclone? If not, can you give me a table or something that lets me know what sized motor and blower I need? Again, you don't want much do you! *Smile*

   1. The first thing to do is to compare your machines against the AAF CFM needs table on my Dust Collection Basics Page. That table shows you need 800 CFM on four of your larger tools;

   2. We next go down that same page and look at the CFM ratings. The maximum you are going to get in terms of airflow from that motor without going over its rated horsepower is 550 CFM. The good news is that if you really have a 12" impeller, you can upgrade to a 2 hp motor and get 874 CFM at 6" of static pressure;

   3. Next we fire up the static pressure calculator and enter in 2 each 90 degree bends, 1 dust hood, 14' of duct, 3' of flex, 3" of pressure for using my cyclone, and 0.25 for using a pair of huge fine free flow filters. The machine kicks out a mere 20.13" of static pressure. Easy, go find a 15 horsepower motor and 20" fan (I'm guessing as my tables don't go that high); and,

   4. Ok back to the drawing board. Let's toss the 4" duct and hose away and replace all with 6" and see what happens. Feeding in exactly the same numbers but with 6" hose and ducting, gives us 6.14" of static pressure on your longest and biggest demand run. Going back to the fan table we see that with a 12" impeller we can get 874 CFM with 1.83 horsepower and 783 CFM with 1.71 horsepower, exactly what we need for a minimum. That would smoke your 1.5 horsepower motor, but a 2 horsepower would be fine. The bottom line is you need at least a 2 hp motor with at least a 12" impeller to power a cyclone with hardly any ducting. To maximize your airflow you should step up to a 13" with at least a 3 horsepower impeller, or go with an airfoil and live with the cleaning, and having to keep a blast gate open.



Cyclone General Information

1. How do I keep the inside of my cyclone from wearing or rusting through?
   Controlling corrosion, rust and wear is not that much of a problem. Yes, sawdust contains silica (sand) and moisture that will quickly (a few years) eat through 24 gauge galvanized metal. If you make your own cyclone you should use galvanized metal and spray the inside with the rubberized (not asphalt based) auto body undercoating. An even better solution is to have the inside sprayed with that Line-X truck bed coating. I also use a piece of rubber sheet that covers the area where the air first hits on the cyclone body to further reduce wear.

2. What is the difference between a pull through cyclone and a push through cyclone?

   1. A pull-through cyclone locates the blower after the cyclone creating a pull the air through arrangement. It is the configuration that most use because the cyclone acts as a pre-separator (sometimes called two stage) to keep material from hitting the impeller as well as a fine separator to minimize filter clogging.

   2. A push-through cyclone locates the blower before the cyclone. It is more efficient for small blowers because it does not have to overcome the initial resistance of both the ducting and cyclone. The big disadvantage is material does hit the impeller directly so these must be powered by heavy material handling impellers.

3. In your opinion am I further ahead to make a Push or Pull cyclone system? What are the advantages of each?
   In theory both a push and a pull through cyclone should be equal. But because hobbyists tend to use small motors that leave our blowers either air starved or right on the border of being air starved, the push is more efficient because it can get the air it needs to work. The advantage to the push through is you do not have to worry so much about leaks in your cyclone and collection bin and being able to use a heavy plastic bag for chip collection. Unfortunately, the push through is not nearly as clean of an overall design as a pull. With a push through design, there is no separator to protect the blower impeller from material hits. This poses a potential fire hazard, so most including me use pull through designs.

4. How do I optimize the performance of my cyclone and what if any maintenance should I do to ensure good airflow?
   Although I provided a ducting resistance calculator, the bottom line here is you need to follow a few rules to ensure optimal dust collection as well as the safety and longevity of your impeller and motor:

   1. Use an efficient cyclone placed before the impeller;

   2. Use ducting and ducting runs with minimal resistance;

   3. Use at least one five foot long run of 6" ducting/hose to your larger machines;

   4. Use large minimal resistance filters;

   5. Keep your filters clean enough that they don't create too much back pressure;

   6. Keep an eye on the overall pressure/amperage of your system to make sure it is working efficiently.

5. I doubt that you will answer these two questions, but which commercial cyclone would you buy if money was no object? And, which would you purchase if funds were a little tighter?

   1. I'll answer, but with a little qualification. Unlike most hobbyists, I am going the other direction having done woodworking professionally for a long time and having moved into fine woodworking in a much smaller shop to please myself and make things for friends and family. I'm in my fifties, have been fairly successful with my career, and have spoiled myself with quite a few high end hobbyist and low end industrial tools that require more than the normal 800 CFM required by most hobbyist larger tools. I also have a large three car garage with tools all over on wheels so I can also comply with my homeowner rules and park my cars in at night. As such, my first choice with my three-car garage sized shop and larger tools would probably be a large Felder collector. The Felder is certified to provide the airflow and extra filtering I need to deal with my asthma. My second choice would be a seven to ten hp Donaldson made Torit cyclone with their special fine 0.2 micron filters. Dust Vent would be a near tie for second.

   2. In a tighter money situation, I would still either make a cyclone from my plans or buy one from Clear Vue. You can build your whole unit yourself using my suggested plans and parts suppliers, or buy the same thing from Clear Vue ready to install with 5 hp motor, blower, impeller, and cyclone for about the same cost as building your own. I would configure my cyclone with the ability to blow the air outside most of the year except when really hot, then would filter it. Cold is not much of a problem because I use radiant heaters that keep me warm in spite of fairly low outside temperatures.

6. I appreciate the considerable work you have done and shared on dust collection and cyclones, why don't you just go one step further and build a commercial cyclone and blower that we can buy?
   I'm pretty involved in my own world and just don't need or want another career or business at this point in my life, saying nothing of health problems that severely limit my activity. My son cut cyclone kits for local friends starting in 2001, but had more work than he could possibly do without any advertising other than word of mouth. In early 2003 I turned that kit business over to a fellow in trade for a small commission and his doing all the work. He dumped most of the work to run that business on me and failed to pay a penny, so I took away his right to make more cyclones after giving him multiple chances to make repair. He and his friends were pretty upset at me and came out with a lot of very untrue and negative nonsense. They all loved how well their cyclones worked, so instead attacked my son who took back over that business saying it was far too hard to make our kits. Yes, the metal work was a little difficult, but not that bad and saved quite a few hundred dollars in cost to end up with a far better cyclone than anyone else offered. My son built his existing supply of kits into completed cyclones and was overwhelmed with orders. I pulled the plug because he could not keep up and FedEx, UPS, and USPS kept proving that sheet metal cyclones do not bounce well. We ended up losing money over all the shipping damage and I said enough. He still cuts a few kits for local friends between his busy schedule at college and playing competitive tennis. We had so many destroyed cyclones that now only USP will do our shipping if we have them do the packing and pay a premium in insurance running our shipping cost over $130 depending upon where you live.
   
   As far as this web page work goes, I did my dust collection and cyclone work to keep myself busy while recovering from some pretty serious lung problems with hopes of returning to my own hobby. Keeping this all up and answering the numbers of questions that keep coming my way is nice, and I do enjoy helping others, but has far too long been a major time and dollar eater taking away from other parts of my life. I suspect that as soon as I find someone to take it all over, I am going to step out of this arena and return to other activities leaving what I've done for others to consider, then make up their own minds.



Dust Masks and Respirators

1. Bill, I have a coarse beard and it leaks badly when I wear my 3M model 7500 dual cartridge respirator mask you recommend. I see you have a beard, do you have this same problem and if so what do you recommend for me?
   I strongly recommend to those without beards that same 3m model 7500 dual cartridge respirator mask that you use. Since it comes in different sizes you should get one that fits your face comfortably. The paper masks leak far too much for woodworking. And yes I have a beard and it does cause some leakage but probably not as much as most as my hair is very fine and most has already fallen through going from the top of my head and out my nose, hands, ears, etc. Seriously, I pull my mask extra tight whenever making just a little fine dust or doing a little painting or spraying. It still leaks more than I want, so when making more than a little fine dust I end up wearing either my 3M or Racal Powered Air Purifying Respirator (PAPR). Both are near identical except my 3M also came with a second flip down welding mask visor option. Given Racal stopped making their units and the 3M are pretty pricey, for most I recommend that 3M 7500 unpowered respirator mask.
   
   For turners, those with heavy beards, and those developing some sensitivities my turner friends like the Trend Airshield powered respirators with face shields that work great with beards because the air just gets blown out through any leaks instead of us sucking stuff in. The new Trend Airshield Pro is a near exact copy of my far more expensive 3M and Racal respirator masks. I would like to hear when people begin buying these how well they work. Also, be careful what you buy has easy to find and affordable filters. I have a new off brand mask whose maker went under and you can no longer get its unique filters.



Filters and Dust Bags

1. Bill you have really confused me on the whole subject of filters. I read on your pages over and over that what is best is to either place our dust collectors outside or blow the air from our cyclones directly outside. Then you go into great detail why your cyclone is the best to protect our expensive filters needed to amply protect our health. Please help with this confusion
   You are absolutely correct. I recommend all dust collectors be placed outside and all cyclones be vented outside. In many areas due to legal requirements like where I live, other limitations, or extremes in weather venting outside all the time is not a viable option. If you have to vent inside, then I am not in favor of using any of the dust collectors because they just put too much dust into the filters. Likewise, I am not in favor of using any but my cyclone design for the very same reason. What I do recommend is using my cyclone design if you have to filter and whenever possible setup your system with a wye and blast gates that let you direct the air from your cyclone outside whenever weather permits. The rest of the time, you can send the air into your filters.

2. I like to know more about the performance of different DC bags with regard to airflow and filtration.
   My personal testing was done 1999 through 2003 and then there was not a single dust collector or cyclone filter bag I tested that was suitable for indoor use in spite of many advertised as 0.5 to 2-micron filters. Although I suspect some of the worst I identified earlier have improved, I still see nothing at all in the filter maker literature that says any dust collector or cyclone bags have good enough filtering or enough area in to safely use indoors. Yes, a finer bag will flow more air because the finer filter particles offer less resistance. Likewise, the finer filters will filter far more dust, but most freely pass almost all the PM 2.5 particles (particles 2.5-microns and smaller) close to 100% of the time. Do a Google search on “PM 2.5 health risks” to see over 8,000,000 references to explain why letting this stuff into your shop that can so easily spread into your home, particularly with indoor and basements shops is not a good idea.

3. Bill, I am developing some dust allergies and my daughter who works with me in my basement shop now has developed full time allergies that get so bad in the shop she can only work for about twenty minutes before having to quit. I have a big brand name 2 hp dust collector, upgraded as you recommended long ago to all 6” duct, already fixed my tool hoods and ports, plus bought what is supposed to be the best quality bag filter available. None has helped either of us. We live in an area where our neighborhood rules preclude moving the dust collector outside. What do you recommend I do for filtering?
   As discussed on my web pages I suspect you have a very clean looking shop because a 2 hp dust collector does an excellent job of “chip collection” and your fine filter bags will get rid of most visible dust and dust buildup overnight on your tools. At the same time based on your allergy symptoms you and your daughter are walking test gauges that prove your solution is not doing a good job on getting the fine dust. In short I seriously doubt that your 2 hp dust collector moves or will ever move ample air to collect the fine dust from your tools, plus your fine filters probably pass almost all of the finest unhealthiest dust known to cause the most long term problems. Sadly, I get a few emails a day from people telling me exactly the same thing about building up dust sensitivity while using near identical dust collection systems and fine filter bags. These dust collectors with the fine filter bags just do not protect us from too much exposure to the finest unhealthiest dust.
   
   Because basement shops tend to share air with our homes, we often end up with a 24 x 7 exposure, so you should get you, your daughter and any other family members with symptoms to a good doctor and probably allergist who can evaluate what is going on. If these allergies are wood dust triggered, and it sounds like they are based on your daughter’s symptoms, then immediately stop all your woodworking and do a major shop and home cleanup. I’d recommend you wear a good dust mask like the 3M 7500, use a leaf blower, and use your dust collector blower with the output going into a big hose snaked outside instead of to your bag tree. Likewise change or replace your home filters to fine filters then clean or replace them right after your shop clean up.
   
   In your situation I would recommend building or buying a cyclone of my design from Clear Vue with a couple of the big Wynn 0.5-micron filters plus one of the big Wynn HEPA filters. The reason my cyclone design is important to you is because it separates off almost all of the finest dust providing far better protection for you and your family and gets rid of most of the dust that clogs and destroys fine filters. It is over 98% efficient at separating off the 30-micron and smaller particles, versus its nearest competitive cyclone at only 42%. This twenty-nine fold reduction in fine dust makes for better health protection and much less filter cleaning and far longer life on these expensive filters. It sounds like your area will allow you to exhaust outside, so I would setup this system with a wye that can either filter or blow outside. I recommend you blow outside except in the most extreme weather. Remember when blowing outside you should provide makeup air and a carbon monoxide detector to ensure you don’t suck deadly gas backward through any flues, vents, or chimneys. It sounds like you have already got the ducting, tool hoods, and tool ports covered so other than the time and expense to upgrade, this should work.
   
   So to answer your question as to what I recommend for filtering for those who have allergies and still want to continue woodworking. You must have and use a good mask when making find dust. Likewise, you should build a plenum better known as a box where the air blows through your pair of the big 0.5-micron filters then out the box into a big HEPA filter. This is what I do. I had Rick Wynn with Wynn Environmental help me with sizing all and getting me the needed filters. He said this is the best way to go because our 0.5-micron filters will do a great job of protecting the HEPA filter allowing it to last nearly forever.

4. I can see why two of the larger filters will reduce flow resistance by four fold (double the area and half the velocity through that area), but why does it also increase filter life by four fold?
   What kills filters is dust loading and pressure. The reduced pressure does not force the high silica (glass) content in the fine dust to cut and tear it way through the filter pores as quickly plus the caking of this fine dust is much slower, thus the much longer filter life.

5. When and how do I clean my filter bag?
   Knowing when to clean your filter is mostly a matter of feel or buying an air gauge. If the flow is falling you need to clean. When to replace your filter is tougher. You have to monitor particulate count, pressure, or be conservative and do early filter replacement. With particle counters far too expensive for most, it comes down to buying a pressure gauge and carefully tracking the pressure or just regularly replacing filters. When the pressure starts dropping after each cleaning your filter is near if not already needing replaced.
   
   Here is how to do that monitoring, at least what works for me. Put an air gauge on your system when you get new bags. For this to work you need a consistent situation. For those with ducting I suggest running with your two closest largest ducts open and all else closed. If you do not have ducting, then test with only a 10’ length of flex hose connected. First record the pressure with no bag then with your bag. The difference is how much resistance your bag adds. Next record the pressure every time you clean your bag by either vacuuming or blowing it down. Don’t use more than 40 PSI to clean your filters or you will kill them early. The pressure should rise rapidly for the first three cleanings then slowly rise for the next six or so. Then the pressure should stabilize after every cleaning. When the pressure fails below its normal after cleaning pressure, it needs attention. If you have a blended poly paper filter like most cartridges, you need to replace the filter. If you have an all poly heavy filter bag or cartridge you need to run the filter through a washer and start over. If the pressure does not quickly build up to the same prior resistance levels, then that poly filter is probably shot and needs replaced.

6. Why do you recommend cartridge filters instead of the much less expensive filter bags for dust collectors?

   1. The main reason for going with a cartridge is they provide the finer filtering in a smaller package with the much larger surface area needed to protect your health.

   2. Cartridge filters can also be configured in an easy to clean filter tree that does not give you the nasty dust bath you get every time you need to clean your filter bags.

   3. Cartridge filters also have far less resistance and resistance kills blower performance you need to collect those fine particles at their source. A typical dust bag is a 20" diameter circle and roughly 24" in height. That gives about 1508 square inches of filtering area which is about 10.5 square feet. A small Torit compatible filter is 12.75" diameter and 26" to give 226 square feet of filtering area. A pair of these for me cut the backpressure down from over 2" to 0.25". A single 300 square foot cartridge typically has about 0.5” of resistance. I now use two of these and get less than 0.2” total resistance. These lower resistance levels translates to many hundred more CFM being available at my machines to collect the dust and having to empty or clean my filters about 1/20th as often. That’s important to me because I need the airflow and know that cleaning rapidly wears out these expensive filters.

   4. Sadly, I do not see hobby bag and cartridge filter makers getting NIOSH or ASHRAE certification to back their filtering claims. What I do see is firms presenting filtering numbers that are based upon collector bags being about three times more caked with dust than they can handle and still pass enough air for good collection. I suspect most would empty these bags before they got one-third that dirty. Highland Hardware is a long time favorite because they tell things straight. I believe they and American Fabric Filter have some of the best bags, yet Highland sells their 0.1 micron filter bag, which I believe is one of the best, yet they admit right up front that it really is not that good in real use. If you carefully read their catalog advertisement, you will see that they think it is really only effective at 1/10th to 1/20th its actual rating. We will not know until the others submit to certified testing, but I will not buy the 3, 5 or even 10 micron rated bags for my own use. Before filtering claims can be believed you need to know at what CFM they are rated and what percentage of the claimed particles they capture at that CFM. If the firm can not tell you that, then they probably should not get your business.

   5. The solution is to go to NIOSH or ASHRAE approved cartridge filters. Most use a cyclone separator to protect these filters from material hits that will quickly ruin them from the chips poking holes in the filter material. The cyclones separate most of the dust so the filters do not clog too quickly. Cyclones take a lot of CFMs to operate as they do a lot of work spinning the air around to use centrifugal force to separate off the particles. Most hobbyist type cyclones need at least 3/4 HP additional capacity in your dust collector motor and a much bigger, more efficient impeller to power the cyclone, so if you are planning on eventually adding a cyclone, you should be looking at a 2 HP unit or larger. A few have made impeller changes and modifications to the 1.5 HP units, but the result ends up only being ample for a pretty small shop.



Carving

1. Bill, I’m a power carver who has converted a room in my home to doing my woodworking. I mostly use sharp knives, but do my rough work with a rotary power carving machine. I also use a nice small long narrow belt sander. I’d like to get some dust collection because I am finding dust all over the house. My budget is limited to $200. What do you recommend?
   Woodworking in a basement shop or spare bedroom in a home sealed against below zero temperatures is asking for trouble, particularly if you use any toxic woods or something like a power rasp or sander. I’d like to see you take the power carving and sanding out to your garage and just do the cutting type work inside. You should never work on toxic wood indoors. This would be the woods with two or more pluses indicated on my Wood Toxicity Table.
   
   If you have to do these dustier tasks inside you really should get pretty serious about good fine dust collection and strongly consider buying the portable cyclone from Clear Vue Cyclones. With your tight budget constraints you can make your own or mail order purchase from Woodcraft a carving dust collector hood which will help considerably. These hoods mount a number of small electronics cooling fans behind a filter and surround that with plastic sides and top to pull in most of the fine dust that you make. I asked one of my carving friends how well it works and it says it misses the larger particles that get shot off by his Foredom power carver, but gets most of the fine dust.
   
   I also recommend you buy and use a Fein Turbo III shop vacuum upgraded to a Sears red-line fine filter. This is the most powerful and quietest of the regular shop vacuums I’ve tested. I’d suggest you make a mini hood and use it attached to this vacuum plus that power carving dust collector.
   
   Now is this going to do the job? Not entirely. That’s why should also step up your filters in your home to the finest you can get plus use a good sized air cleaner in your work area. I use a big Honeywell cleaner in my home with both activated charcoal and fine HEPA grade filter.



Metal Working

1. I am a metalworker and not a woodworker but I still feel that I have dust control issues in my basement workshop. I need to control the dirt generated by a Baldor 2 inch sander and a Baldor 1 inch belt sander. These are used mostly for metal but sometimes for other things too. I really don't think I need anything too fancy but I would like to get your opinion. I also have some grinders that can generate a lot of dirt. Do you think a simple bag type blower is adequate?
   Similar to woodworking you have some of the same collection issues.

   1. To collect the dust you have to block, contain, direct and present the material for collection. I suspect that like most woodworking tools this will require you to remake your tool hoods to ensure doing the job.

   2. You need to move ample airflow to collect the material and transport it through your ducting or hose. With woodworking lots of testing has shown that most wood dust is collected well by having an airspeed of 4000 feet per minute (FPM) being pulled by about 2” of pressure. Although we can transport the dust with about one third less airflow in horizontal ducting runs, vertical runs need close to that same airflow to keep from plugging. Because metal is heavier, it needs a higher airspeed to both collect and transport it in the ducts. The Cincinnati Fan Engineering Data PDF is one of the best and most concise discussions on material handling that I have found. It says you need 5000 FPM at 3" of pressure to amply collect and transport the metal debris.

   In working metal you also have a few more problems than woodworkers.

   1. Metal can launch sparks that can burn for quite a while when fed by a powerful blower. To address this you should avoid typical woodworking cardboard dust bins, felt bin bags, and plastic bin bags. Instead use metal ducting and ensure you have a metal can for collecting the chips.

   2. Many metals either contain or are coated with materials that when vaporized by sanding or grinding are very unhealthy to breathe. That means you should always wear a good mask like the 3M 7500 with cartridges appropriate to what you are doing. I personally just bought a case of their high end organic vapor cartridges plus HEPA grade pre-filters and only use that one setup for everything. The drawback is the activated charcoal requires storing my mask in a sealed plastic bag when not in use plus regular filter changing.

   3. Since almost none of today's affordable dust collection systems have appropriate filters, you really need to exhaust the air from doing your metal collection outside.

   In terms of what I would recommend, try and find a 55 gallon drum mounted 2 hp or larger dust collector that you can put outside. Cincinnati Fan, Grainger, and quite a few other firms make these kinds of units. A cyclone would also work well for you, but it costs about 50% more overhead to force the air to turn in the tight internal separation spiral, so you will need a 3 to 5 hp cyclone to get the same airflow you would get with a good 2 hp dust collector.