Table of Contents
(click on topic to go there)
- Work Outside
- Work Inside
- Specific Requirements
- Blower Selection
- Ducting Selection
- Filter Selection
- Cyclone Separator Selection
The problem is simple, woodworking makes too much fine invisible dust and this dust lasts nearly forever unless it gets wet, so those who vent their dust collection systems inside invariably build up such dangerously high amounts of fine invisible dust that just walking around without doing any woodworking launches enough fine dust airborne to fail EPA air quality tests. Government testing shows on average with every twenty pounds of sawdust that we make, we also make enough fine dust to cause 15,141 typical two-car garage sized shops to fail an EPA air quality test. The EPA sets tough standards for indoor air because the peer reviewed medical research clearly shows every exposure to any kind of fine dust causes a measurable loss in respiratory capacity and some of this loss becomes permanent. Wood dusts are particularly nasty because fine wood dust particles are covered with razor sharp edges and sharp, often barbed points plus wood contain and carry many toxic chemicals. My Medical Risks web page shares far more detail than most ever want to hear. The bottom line is most small shop workers who vent their shop vacuums, dust collectors and cyclone systems inside get more fine dust exposure in a couple of hours than most full time large commercial facility woodworkers get in months of full time work. That should terrify small shop wood workers, because even at their much lower fine dust exposures, the insurance data shows large facility commercial woodworkers all lose about 1% of their respiratory capacity per year of woodworking, one in seven ends up with such strong allergic reactions they have to stop working certain woods, one in fourteen is forced into an early medical retirement, and about two in a thousand end up with nasal and respiratory cancer. Personally, I got badly blindsided by a nasty allergic reaction that inspired me to invent a better separating cyclone and share these pages. After my own serious health losses I strongly recommend only going after good fine dust collection. The real challenge for small shop owners is trying to make sense of the huge amount of contradictory information and poor products that promise but do not deliver good fine dust collection.
Figuring out dust collection remains a very difficult challenge because of the confusion caused by almost every small shop source of information gives different advice.
Most small shop owners learn their crafts from others who have spent generations refining their techniques. We build considerable respect for the expert crafts people who turn out such incredible work. We then assume that if we follow their lead in dust collection, particularly with most of us only able to work a little part time, we also will enjoy many decades of trouble free production. Unfortunately, dust collection is very poorly understood and rarely do we get to hear the rest of the story. All are more than pleased to share the beautiful project along with the techniques that made that project possible, but nobody wants to share the related short and long term health problems. and who do not that after a lifetime of woodworking we have developed worse COPD resulting in far more loss of respiratory function than happens to most heavy smokers. I was shocked after putting up this site that I was contacted by some pretty big name woodworkers some of whom are or were considered the best in the world. Most told me in private that they had developed serious problems after a lifetime of woodworking. One told me he had to give up doing work himself and can only work through helpers as he can no longer even be close to wood dust. Another told me he was forced to stop writing articles. A respiratory doctor contacted me and shared that one of his patients is a well known television woodworker and he had to stop woodworking due to long term respiratory damage. Although much of woodworking involves learned skills, dust collection is unfortunately an area where there is more bad information than good.
Dust collection means very different things to different people and the controversy over the cost to implement good dust collection has resulted in lots of very impressive studies by very authoritative institutions that "prove" airborne dust is only a nuisance and does not pose any serious health challenges. in different areas and to different groups. Many urban areas now require larger commercial facilities to provide excellent chip protection and to hold facility air quality below certain levels. This material shares how to figure out how to meet the various levels of dust protection. This information was originally shared on my Dust Collection Basics page then moved here after too many said it needed to stand alone and be simplified. Regardless, because most available dust collection solutions do not protect our health, I think everyone should first determine what they need in dust collection before making a dust collector or cyclone purchase decision.
The only regulation of the small shop market comes from what we choose to make or buy. Unfortunately, for far too long small shop owners have made purchases based on vendor dust collection information that flagrantly lies or gives extremes that we will never see in real use. The only way we are going to get our small shop vendors to behave is to make much more informed decisions that acquires equipment to meet our specific objectives. Most choose between doing either chip collection or some level of good fine dust collection.
- Chip Collection collects the same dust that we would otherwise sweep up with a broom. Chip collection helps protect against falls, injuries, and fires, plus keeps it so we can see our work. Good chip collection has been required in some areas since the 1920s so is very well documented and understood. The major vendors share on the Internet exactly what we need to do to get good chip collection. For decades chip collection was what people meant when they referred to dust collection. Most dust collection equipment makers provide tools only set up for chip collection. Most also only share what is required to get good chip collection. The first step in good chip collection is making sure that all of our tools have ample hoods. Most tool blades, bits, cutters, and even sandpaper launch dust filled air streams at 100 miles an hour or faster. Dust collection blowers typically move air at less than 45 miles an hour. A forty five mile per hour air stream will not capture a 100 mile per hour air stream without help. What There is zero chance of success meaning good collection collection solutions is to make sure our tools have hoods that contain, direct and deliver the fast moving debris filled air streams for collection. Almost all small shop stationary tools get good chip collection if we use good hoods and provide about 350 cubic feet per minute (CFM) air volume moving with an air speed of about 4000 feet per minute To avoid fine dust problems from woodworking we can work outside with a good mask, or work inside and either blow that dust outside or filter our air.
- Fine Dust Collection provides good chip collection plus keeps the airborne dust levels below industry standards. Since there are no standards for small shops except what we put in place ourselves, we have to make a decision then install the dust collection to meet the standard we chose. At one time there were dozens of different air quality standards for all different kinds and types of materials. Worse, standards were area specific. For instance where I live in California it is illegal for me to vent my hobbyist woodworking equipment outside, yet a quarter of a mile away in an unincorporated portion of our same county, commercial shops must vent their dust collection systems outside or use very expensive systems that are certified as fire and explosion proof. Today, the research is clear that almost all airborne dust is very unhealthy, so both the U.S. and European Union now are moving toward a universal standard that allows no more than about 0.1 milligrams of fine fine dust per cubic meter of air. Many areas have not adopted these standards for all dust collection, but many have not. This means in my area when I say dust collection it means good fine dust collection versus crossing the road into the county area dust collection only means chip collection. Clearly, we end up with a lot of confusion and because almost none of the older or small shop equipment is set up for good fine dust collection, implementing good fine dust collection is a considerable challenge. The good news is the very few major commercial dust collection system makers who guarantee customer air quality, share exactly how air engineers and shop owners must install and run dust collection systems to guarantee good chip collection and good air quality. Since small shops use identical smaller stationary tools, this large facility dust collection information that the top vendors share on the Internet is equally usable in small shops. Unfortunately, most of what is shared is designed for air engineers so requires study to be used effectively by small shop owners. The good news is dust collection air engineering is not rocket science and not nearly as complicated as making a nice piece of furniture, so good dust collection practices can be easily learned. The whole rest of this page addresses these challenges.
- Work Outside
When new woodworkers ask for my advice I always recommend they start woodworking as a fair weather activity where we work outside wearing a good certified NIOSH mask with two replaceable cartridge filters when making fine dust. This lets us start woodworking without a huge cost in dust collection equipment or putting our health at risk. Also, thanks to some new innovations in tools, we can do really fine woodworking without having to make the huge start up investments in heavy indoor stationary tools that previous generations of woodworkers needed. I personally do quite a bit of my woodworking outside using a good hand held power saw, router, jig saw, drill, orbital sander, and oscillating spindle sander with a guide system instead of my large stationary power tools. Most find having these basic tools handy and useful around the home even if woodworking turns out to not be a long term hobby. My guide system lets me do fine woodworking just as well without the high overhead of dragging out and setting up my large stationary tools. My guide system offers considerably more ease especially when working with large sheet goods. Festool is known for their hand held power tools with excellent fine dust collection built in that all work with their rail guide system and special table. Although these work well, I found their entry level tools too underpowered and their journey level tools pretty pricey. I also already have a great set of some of the finest hand held power tools money can buy, so went looking for other options that would work with my tools. I found and now use the Eureka Zone EZ-Smart guide system and table that works well with my existing tools. This system is so versatile my daughter and I made her a nice desk in the fall of 2005 without doing any machining or sanding indoors.
- Work Inside
When we want to take our woodworking inside then we either accept the risks and known long term health damage from fine dust exposure or take the time and trouble to protect ourselves and those close to us from this dust. As stated before for good fine dust protection, we need to first fix our tools to protect and control the fine dust so they do not spray the fine dust all over before it can be collected, use a big enough blower and ducting to move the air needed for good fine dust collection, and then get rid of that dust. There are two approaches to getting rid of that fine dust, blow it outside or filter it away. Air engineers long ago learned that filtering the air is not the best option because it requires far more expense with constant filter cleaning and replacement, plus is very difficult to do effectively enough to provide good fine dust protection. As a result almost all commercial dust collection systems simply blow the fine dust away outside.
- Blow Outside
Building regulations and fire codes require putting commercial dust collectors and cyclones outside, so most commercial shops automatically simply blow the fine dust away outside. Their dust collectors use very open filter bags designed to let the airborne dust pass right through. Their cyclones are designed to separate off the heavier particles and they also just blow the fine dust right through again into the out door air. Most with small to average sized shops can put their dust collector outside with no air coming back into the shop. Although this works if you have a big enough collector, few find this a good long term solution. It is very difficult to know when to empty our collectors, yet if they get too full we lose the airflow we need for good fine dust collection. Emptying these units often is a troublesome chore that exposes us to large amounts of the fine dust we should avoid. Many find it a far better option to skip the outdoor dust collector and instead start with the 3 hp or larger cyclone that blows the fine dust after separation outside. A good cyclone does not need a filter, so they avoid the filter mess altogether. They also do such a great job of separation you should never see any dust outside unless you forget to empty the dust bin. Almost all commercial shops use this option with a cyclone blowing the fine dust away outdoors.
Many foolishly worry about blowing the heated air out of their shops when commercial firms have shown that doing so really is not as expensive as trying to filter the air. These large shops have shown for years that radiant heaters keep up the temperature in the coldest of climates without worrying about their huge blowers that turn over the entire air volume many times every hour.
When we blow the air outside, we for sure need to ensure that we provide ample makeup air to replace the air being blown away. Without enough makeup air we can suck deadly carbon monoxide backward through the flues for our appliance, heater, stove, fireplaces, etc.
- Filter the Air
Unfortunately, many like me cannot put our dust collector outside or blow the dirty air outside. We have zoning problems, neighbors, noise concerns, cooling problems, concern with drawing deadly carbon monoxide into our shops, etc. that require us to return the air to our shops. Filtering our air is something rarely done by large commercial shops because filtering opens a bucket of worms. We need not only fine enough filters to protect our health, we need filters with enough surface area to protect the filters. Using filters with too little surface area kills needed airflow and causes the filters to quickly self-destruct.
- Chip Collection Standard
Air engineers long ago did the research and testing to determine what was needed to comply with government fire and safety requirements to keep the chips and sawdust collected instead of spreading all over our floors. They found almost every stationary woodworking tool required a collection hood upgrade and moving between 350 and 450 CFM for good “chip collection”. Fire safety and building codes required putting almost all dust collection equipment outside. Between keeping this equipment outside and the use of huge blowers that blow almost all of the airborne dust away, fine indoor dust pollution was not initially considered a serious problem.
- Fine Dust Collection Standard
Wood dust contains silica, better known as glass so long term exposure affects our health similar to smoking tobacco or exposure to fiberglass insulation or asbestos. Over time all with enough exposure eventually become ill, some seriously. Unfortunately, insurance data and medical testing in the seventies showed airborne dust is a serious problem that caused almost all woodworkers in large commercial woodworking facilities to eventually develop wood dust related health problems that became so bad about one in eight was forced into an early medical retirement. Facility owners fought regulation hard.
Eventually OSHA finally compromised putting in place its 1989 air quality standards and testing but nobody has been happy since. Insurance data show workers protected to current OSHA standards almost all eventually get ill from long term fine dust exposure with about one in fourteen still forced into an early medical retirement. At first facility owners blamed prior higher exposure levels, but that argument died as too many younger workers became ill and these younger woodworkers never were exposed to the higher dust levels previously permitted. At significant risk of losing personal injury suits in the face of this insurance and medical information, most large commercial woodworking concerns voluntarily adopted the five times tighter standards recommended by government industrial hygienists (ACGIH). Many medical researchers and respiratory doctors instead recommend the fifty times tighter medical standards. The European community agrees and has already adopted this more stringent medical standard. Now that EPA showed fine dust a much stronger allergen than originally expected and a cancer causing agent, OSHA is being pushed hard to adopt similar standards, but costs, politics, and controversy have that process stalled.
These standards do not apply to small shops leaving the six out of seven professional woodworkers that work in small shops along with all hobbyist woodworkers with no regulations, oversight, standards or protections except what we put in place ourselves.
- Chip Collection Standard
My respiratory doctor, one of the top specialists in our area, said almost all small shop woodworkers and our families often receive far higher fine dust exposures than professional woodworkers that work full time in large commercial woodworking facilities. He blamed these high exposure levels for putting me in the hospital and my allergy tests confirmed he was right. Unable to understand how my top rated cyclone with upgraded finer filters could cause this problem and wanting to know just how bad it was, I had a medical air quality test run on my shop.
My air quality inspector started off saying my doctor was probably right as my shop would probably fail the airborne quality tests. He explained the government tests small shops as they apply to increase their numbers of employees and almost all fail their tests. He said small shop woodworkers buy from hobbyist vendors. These vendors and we as their customers have no OSHA oversight except what we exercise with our purchase decisions. Most small shop woodworkers know little to nothing about fine dust hazards or collection, so we keep making bad decisions. With no incentive to change, our vendors keep selling “chip collection” long after the 1989 OSHA requirements forced commercial firms into fine dust collection. Chip collectors do a great job of picking up the same sawdust and chips we would otherwise sweep up with a broom, but only move about half the air needed for good fine dust collection, plus come with wide open filter that pass almost all the airborne dust turning them into “dust pumps” that keep our shop air filled with high levels of airborne dust. He said the only reason our shops do not test with even higher airborne dust levels is air will not hold higher concentrations long enough for the tests to complete.
I explained I understood this which is why I bought the “best” rated cyclone with an upgraded large fine filter. He explained I trusted a vendor that has no oversight or regulation to ensure their equipment actually works. He explained the minimum airflow we need is about 800 CFM at our larger tools for good fine dust collection. Testing with just one run open at a time measured no airflow over 400 CFM to any of my machines. He explained air at typical dust collection pressures is more like water and will barely compress at all. My “professionally” configured ducting used ducting far too small to carry the needed airflow. Using that small duct was like wondering why there was no water flow when the valve was mostly closed. He explained the maximum airflow possible from my blower might move plenty of air, but when challenged with the resistance of my ducting, hoods, tools, flex hose, filters, and the high overhead to run my cyclone there was nothing left for dust collection.
Worse, my cyclone just like almost all other small shop cyclones poorly separated the air causing a serious filter problem. He explained almost all small shop cyclones are downsized outdoor cyclones engineered to push almost all the fine dust right through where it would be blown away into the outside air. He said bringing these units inside with wide open outdoor filters turns these units into “dust pumps” that fill our air with dust. Although I was smart in buying an upgraded filter, I needed far more filter area to keep the filter from quickly getting ruined. My cyclone blew near 100% of the fine dust into the filter causing it to quickly clog. This clogging kills airflow well below what we need at our larger tools for good fine dust collection. Worse, the increased pressure as this clogging builds into a cake of dust forces the finest particles right through the filter pores tearing them open. The required frequent cleaning also opens the filter pores as do hits from chips and strong blasts of air. Soon even the best fine filters become useless. His particle counters showed my near new filter freely passed almost all of the fine airborne dust. He said our fine filters may give us a short window of protection, but they then leave a long period of false security when we think we are being protected, but really are not.
He said the worst problem in my shop was trapping the finest near invisible dust inside. It takes six months or longer for this fine dust to break down and dissipate, so when trapped indoors it builds to dangerously unhealthy levels. Almost any air movement from our tools, vacuums, air compressors, and dust collection equipment will launch this previously made dust airborne again. He said this finest dust sized smaller than 2.5-microns (PM 2.5), about one fortieth the thickness of a human hair, is near invisible even when it builds up to a fairly thick coating. It slips right by our bodies’ natural protections and lodges deep in our tissues causing the worst long term health problems. He suggested I do a Google search on PM 2.5 health risks to see EPA and over 300,000 other sources have to say about the dangers of these fine particles. He was right. Please look at my Medical Risks web pages for more information.
His prediction was right as my shop tested with double the OSHA allowable airborne dust level with a fine particle count that was 12,000 times higher than considered medically safe, plus my home air was also badly contaminated. He explained this fine dust gets carried in shared air, on our clothes, in our hair, and on our skin into our homes, offices, and vehicles exposing all close to us. He said these statistics and health risks should scare the ever loving out of us because we as small shop woodworkers consistently have far higher airborne dust exposures than commercial worker who almost all eventually get ill, many seriously. He warned repair would not be easy as I had to fix my tools, get a bigger cyclone blower, replace my cyclone, and replace most of my ducting. That testing confirmed I not only had a problem, but also repair was not going to be that easy because I already used the top rated cyclone and ducting which landed me in the hospital, so repair was not going to come from wasting my time further on small shop dust collection that remains stuck delivering “chip collection” technology.
- General Requirements
It took a lot of work to figure out how to determine my own needs, and then even more work to figure out why my “best” rated hobbyist equipment was not meeting them. With a choice of either making repair or giving up my lifelong woodworking hobby I spent my considerable down time doing the research to understand what I needed, understand why my current equipment did not work, and then personally do the engineering to fix the problem in my shop. When back on my feet I built and refined my solutions so they worked well for me. My doctor pushed me hard to share what I learned and my designs. I did and ended up in the middle of an ugly war where vendors would rather lie than spend the time and money to protect their customers. Many vendors have hammered me unmercifully saying I know nothing, have no expertise in this area, and keep giving out bad advice and using scare tactics to harm their sales. Frankly, these are the same vendors that supply dust collection solutions responsible for consistently failing even the very lax OSHA tests. Regardless, six years later after sharing my information and solutions, almost all of the hobbyist dust collectors and cyclones are the same as they were then, sometimes with slightly better filters. Frankly, today there are no standards for small woodworking shops so the only way we will get good fine dust collection is for each of us to do our own homework then put in a lot of work to assemble our own fine dust collection system.
Complying with the OSHA air quality standards taught air engineers long ago they had to fix the tools so they do not spray dust, capture the airborne dust at the source, and then get rid of it. Otherwise their commercial customer shops would fail government testing. Any fine dust that escapes capture rapidly spreads to evenly fill the air in our shops and any areas with connected airflow. It also gets carried on our clothes, in our hair, and on our skin to contaminate our vehicles, offices and homes exposing all close to us. Failure to collect the dust at the source as it is made leaves the air full of dust that takes a powerful exhaust fan or air cleaner too many hours to bring down enough to safely take off our dust masks. During that time the airborne dust levels are unsafe and often well beyond government standards. The same general requirements apply for our small shops. We must fix our tools to protect and control the fine dust and move enough air to capture the fine dust at the source at each type and size of tool, and then get rid of that fine dust. Moving enough air requires we move the air fast enough for good collection measured in feet per minute (FPM) and move enough volume of air to cover the area from which we need to collect. Volume is measured in cubic feet per minute (CFM).
- Tool Upgrades
Fortunately, professional air engineers have shared out their designs to fix the different types and sizes of commercial tools with better dust collection hoods, ports, baffles, and other changes to keep the fine dust under control. These upgrades keep the dust well protected from air currents and then delivered for collection. Because our larger stationary tools are identical to smaller commercial tools, we can use this same information to get the dust controlled at our tools so we can capture it at the source. My ducting pages share the various recommended hood and port design changes. You can also find some excellent alternative hood upgrades on the various woodworking forums.
- Airspeed Requirements
Decide on how much airspeed you need to collect the dust. We must keep the air in our ducts moving fast enough to avoid plugging and building up dust piles. With enough airspeed, the dust stays entrained, meaning kept airborne. As airspeed falls we first get plugging in vertical runs, then piles in our horizontal runs, and then plugging in our horizontal runs. The problems with plugging are obvious, but most don’t realize that piles in our ducting are really bad news. As the airspeed falls below what we need to keep the dust entrained the heavier dust will fall out of the air and create dust piles in our horizontal runs. A pile will grow in height until it constricts the airflow causing the air to speed up and top the pile. The pile then grows in length plugging any down drops it goes by. This is why I recommend putting the blast gates next to the mains instead of down by the tools. There is a small chance of a spark say from hitting a staple or nail can create a duct fire that quickly gets fanned in a serious problem. When we restore airflow say from opening a larger duct downstream the whole pile goes rushing down the duct at once. This creates just about the only time when a small shop dust collection system develops a dust to air ratio that is violently explosive. There is little chance that these clouds will ignite because we rarely are cutting anything or have a source of static that can ignite these clouds before they dissipate. Unfortunately, poorly designed ducting systems and systems with too little airspeed become a constant source of dust piles that slam into and eventually ruin our ducting, impellers, cyclones, motor bearings, and filters.
Air engineers and universities have done considerable testing to figure out how much airspeed it takes to move the various sizes and weights of wood debris created during woodworking. Very fine dust particles are easily moved with low airspeeds of just a few feet per minute, so we must protect the dust from being spread by air currents from our blades, bits, cutters, belts, motor fans, etc. In addition to protecting the dust we must move enough air to overcome normal room air currents. Careful testing shows gases and very light powder wood dust only exposed to normal room air currents can be collected and carried by 50-200 FPM; light powder dust by 200-1000 FPM; and powder dust by 1000-2000 FPM. Light shavings need at least 3400 FPM and dry sawdust needs 3700 FPM. Heavier chips need at least 4500 FPM. Standard air engineering practices tell us to design our dust collection system to maintain 4000 FPM airspeed, This airspeed has years of experience showing it does a good job picking up the dust while keeping our ducting clear of problems. This airspeed also is an excellent compromise ensuring ample airspeed without buying and paying to use too large of a blower.
- Tool Upgrades
- Specific Requirements
- Air Volume Requirements
Decide on how much air volume you need to collect the dust. The next step in dust collection is to determine how much air volume we need at our current tools to collect the fine dust. Airspeed and air volume are related by a simple formula, FPM=CFM/Area where area is the duct or hood collection area in square feet. Measuring the open hood area on our larger tools, dividing by 144 to convert square inches to square feet, and then multiplying by the 4000 FPM flow we need to keep our ducts clear shows most of our larger tools need about 350 to 450 CFM. Years of experience and careful testing proves this is what we need for good “chip collection”. Since we know 50 FPM is ample to collect the unhealthy airborne dust, many wrongly assume these chip collection volumes are enough to also collect the finest dust. In practice we almost all use older tool designs that even with recommended upgraded hoods required for good chip collection allow too much of the fine dust to escape. Air engineers found they needed to further modify our tools to better protect the fine dust and they needed to create a “bubble” of air suction all around our tool working areas out to at least 9” in every direction to keep the fine airborne dust from escaping. Using that collection area we can then solve for CFM and see we need just over 1000 CFM for fine dust collection, nearly triple what we need for “chip collection”.
If we stop and think, most of us already understand why we need to move over three times the air for fine dust collection than for “chip collection”. Speed and volume are what move the air. We know that using a vacuum on blow will move dust all over our shops, yet when sucking our same vacuum will not pickup dust more than an inch from the nozzle opening. A volume of blown air holds together and will maintain its speed for quite a distance, but air pulled by a vacuum comes from all directions at once. This causes airspeed to fall off at about the same rate that a sphere increases in area. From the formula for the area of a sphere at 4*Pi*r*r we see what a huge difference a little distance makes in airflow velocity.
Air engineers tested almost every type and size of commercial stationary woodworking tool and verified this 800 CFM requirement is what we need at almost all of our larger tools. As you can see from this below table that AAF was kind enough to let me share most of our larger tools and more dusty operations all need roughly 1000 CFM airflow. This does not say that you need 1000 CFM at each machine, only at almost every one of our larger and dustier tools. You also should notice that a number of these tools such as the table saw requirements are given with upper and lower pickup requirements. If you don't use two pickup hoods on your same tools as shown in this table, you need to follow the song's advice and change your evil ways! I use this 1000 CFM as a target for evaluating the various dust collector and cyclone options.
- CFM Requirements Table
- Airflow Controversy
There are many vendors that hate my sharing our need of 1000 CFM at our larger tools because their dust collectors and cyclones will not move this much air when working against the overhead of our tools, ducting, filters, and cyclone. Most of these are the vendors that cause almost every government small shop air quality test to fail because their systems move too little air, have too open filters, and they tell us to trap that dust inside instead of doing like the big commercial concerns and blow it away outside. These vendors keep saying all we need to do is fix our hoods then rationalize by pointing out that firms like Festool have proven that roughly a double normal sized vacuum that moves about 100 CFM moves enough air for good fine dust collection. Yes, Festool. Fein, Makita and a few others are doing good things, but most of us buy and use older tool designs that are not engineered from the ground up to totally control the fine dust from when it is made until delivered for pickup. Clearly, unless we have tools engineered from the ground up with good fine dust collection built in and very powerful shop vacuums, we should follow the lead of those who have been doing the job for years, not those whose customers consistently fail to pass air quality tests. Without specially designed tools we need to do just like commercial shops and start by fixing our tools with better hoods, bigger ports, and sometimes more extensive modifications to keep the dust controlled and protected until it can be captured, and then move enough air to ensure good fine dust capture. Air engineers have used and refined their tool modification recommendations and air volume tables for over fifteen years to ensure their inspected facilities meet government requirements. My trusting these hobbyist vendors landed me in the hospital. The medical air quality testing of my shop showed my “best” rated cyclone had too open filters and moved too little air, leaving the airborne dust level in my shop far past what medical testing showed made almost every commercial woodworker ill before the OSHA standards. No wonder I ended up in the hospital.
- Static Calculation
Unfortunately, we cannot just go buy any dust collector or cyclone advertised as moving more than 1000 CFM and get ample airflow or filtering. Vendors advertise maximums not working values. We need our 1000 CFM air volume while overcoming the overhead resistance of our specific tools, ducting, filters, and separator. Actual CFM after taking away normal overhead is about half the blower potential maximums. To pick an appropriate sized blower we need to compute the specific overhead resistance for our shop, then use a fan table that shows us what size impeller and motor we need.
Although we would like to all think that our shops and needs are fairly unique, most of us have very similar requirements. Most of us have shops sized about the same as a two-car garage and most of us choose to only want to collect from one machine at a time. This lets us use a smaller blower that costs less to buy and less to run. We can verify the overall resistance of our shops fairly easily by adding up the resistance of each part of our dust collection system. Most use a static calculator to help with the math. A static calculator will tell us the resistance that our blower would have to lift to overcome resistance of our ducting, flex hose, fittings, filters and separators. Most dust collection static calculators have a problem in terms of working for small shop one run at a time open systems as they are built for large shops that run with all ducting open at once. They also are built without the resistance of our filters or cyclones because they generally come from vendors that assume you will be using one of their products and build in their own product overhead. With considerable help from Don Beale, an air engineer that designed large commercial systems, we built a simple static calculator on my web pages that also addresses the overhead of our filters, muffler, and cyclone. I preloaded that calculator to give the static pressure for an average two-car sized shop with a typical cyclone and filters. Changing it to use the resistance for my low resistance cyclone design and over sized filters makes a huge difference as you can see for yourself. You can change it around to suit your shop and configuration. Directions to use this static calculator are given on the pages, but in simple terms we figure the resistance for the worst case tool and longest possible run. That ensures we can later move our dust collector and tools around and not be left moving too little air. Our static calculator comes preloaded with the ducting and fittings to go up to an 8’ ceiling from the cyclone across the center of a two-car garage sized shop and then down to a large tool. It then splits that down drop into an upper and lower collection port. The below shows the results of using the higher 3.5” resistance for a neutral vane type cyclone sold by most hobbyist vendors today with they typical supplied “fine” filter. What this calculator does not share is that as the filters get dirty, they can easily add by themselves up to 5” more resistance which is part of why I recommend upgrading to larger sized filters. The other reason is of course that hobbyist vendors have a terrible track record when it comes to filtering claims not coming close to actual filtering performance. Regardless, without upgrading to the larger surface area filters you need to add even more resistance. This spreadsheet says our average two-car sized garage shop with cyclone, ducting, and larger filters will need to overcome about 8.16” of resistance. If uncomfortable with these numbers there are other calculators available and all I have tried show very similar results.
- Air Volume Requirements
- Blower Selection
We need to decide on what type of blower we need, use a fan table to ensure we move enough air with enough pressure, and then ensure that the blower we pick will handle our intended amount and type of use.
- Pressure Blowers
Pick the right type of pressure blower. Pressure blowers that we use to collect wood dust use a fixed speed induction motor turning a special flat fan blade known as an impeller inside a blower housing. There are a few different types of pressure blowers each named for the type of impeller used. Dust collectors and even our cyclones with a full bin send everything collected right through the impeller. This means we need to use impellers made from very heavy metal that can handle material hits. When a blower uses this kind of tough impeller we use what is known as a material handling impeller. Material handling impellers are closed on the bottom and open on the top which makes them self cleaning. There are a few different types of material handling impellers. The simplest uses a radial impeller with straight flat vanes. Radial impellers make huge amounts of noise and only differ from an air raid siren by the speed of the impeller and some internal blower housing clearances. Angling the blades backward creates a backward inclined (BI) impeller that is less noisy but needs a bigger diameter impeller to move the same volume of air. Angling the blades backward and curving them slightly makes for a backward curved (BC) impeller that is quieter and a little more efficient. The WoodSucker II and my airfoil blower designs make less noise and move more air by putting a cage on top of the blades. Caged blowers are rarely found in small shop systems because they are not self-cleaning, so must be placed on the clean side of our filters, plus they require regular inspection and cleaning as any buildup of strings and shavings can throw our impeller out of balance, ruin our motor bearings, burn up motors and cause fires. In addition to collecting debris, the airfoil blowers also have problems with developing destructive vibrations from stalling if the pressure grows as high as most larger woodworking shops develop or if we let our filter get too dirty. Now, almost every small and large shop dust collection system and cyclone system uses backward curved material handling impellers. This means with almost all vendors use near identical impellers. Moreover, blower technology is mature so for direct drive blowers with fixed speed motors the fan tables for professional blowers show near identical airflow. Sadly, the fit, finish and quality of small shop blowers with few exceptions is so poor that most hobbyist blowers perform far worse than the same size and speed commercial blowers.
- Fan Table
Pick the right fan table. Almost every reputable blower maker provides a fan table that professional engineers can use to determine which blower type and size is needed to provide the airflow needed at a given static pressure. Each different type of blower will come with its own fan table that tells what airflow we can expect from a given diameter impeller and known static pressure resistance level. Looking at the various fan tables shows that HVAC squirrel cage blowers do not generate enough pressure to overcome the resistance of our shops. Likewise, we see that our high pressure blowers used in our shop vacuums have ten times or more pressure, but use blower wheels that move too little air volume to provide good fine dust collection. The fan tables show that only pressure blowers move enough air and generate enough pressure to meet our dust collection needs. We can use a standard pressure blower fan table setup for a backward curved impeller to help us pick the right size impeller and motor to meet our needs, and provide a cross check to see if a particular vendor offering will move the air needed at the resistance level within our shop. If we look at the below fan table we find that our 8.16” of resistance and 1000 CFM puts us in a position where there is no exact solution. The 12" and even 14" and 15" impellers do not move enough air at that resistance and a 16” impeller moves too much. Impellers only come in even sizes over 12" unless custom made which you would think forces us to chose a 16” diameter impeller, but the blower makers know many need this 1000 CFM, so most of the bigger blower makers make 15.25" diameter impellers which produce right at our required 1000 CFM.
At typical dust collector pressures, air is virtually incompressible, so any small pipe or opening will act just like a water valve and limit how much flow we get, so our fan table gives us another key piece of information. The fan table blower inlet size also gives us the appropriate size for our main duct going into the blower. With hobbyist systems only running one run at a time, that main tends to be the same size as all the ducting. This means that our fan table calling for a 7” blower inlet pretty much says we also need all 7” ducting. We need to maintain that 7” duct size right to and including our machine ports. Unfortunately, most ducting makers only offer 6" or 8" diameter duct and fittings, so 7" ducting can be very expensive. Many choose the same option I do for my cyclone which is to use all 6" diameter ducting and one size over for my blower so I use a 16" diameter blower to generate the extra pressure to force 1000 CFM through a 6" diameter duct. Without the over sized impeller I would have to use all 7" diameter ducting. Remember, any reduction in surface area will kill our needed airflow. For instance, if we split the ducting into an upper blade guard and lower cabinet collection at a machine, then the area of each of the offshoots added together should be the same or slightly greater than the main or we will kill our airflow.
Our fan table also helps us size the motor for our blower. This table shows it takes just over 3 hp to power a dust collector and 5 hp to power a cyclone and still get our required 1000 CFM. Experience says we can get by with a 3 hp motor turning a 14” impeller for our dust collectors and a 5 hp motor turning at least a 15" diameter impeller for our cyclones, but these configurations will burn up motors if we use larger ducting or run our blowers without ducting attached. The fan table shows that the resistance of trying to run a 3 hp dust collector with 14" diameter impeller 10’ of 8" diameter flex hose could make this blower try to pull over 4 hp, which will soon burn up a 3 hp motor. The bad news is blower motors are tough so we can do this just long enough to do a quick test. Sadly, many vendors do just this which makes for impressive airflows to help with magazine ratings, but also eventually burns up motors. We also can move too much air if we run without ducting, filters, or open more than one ducting run at once. We need to always test each ducting run with an amp meter to make sure our final configuration does not move so much air it overheats and burns up our motor! We can put a blast gate in front of our cyclone inlet and adjust testing with an amp meter to to limit our system to a maximum safe airflow for our motors. Because resistance goes up as our filters get dirty, we often should retest our system after it has run for a few months with a freshly cleaned filter. This exercise with a fan table shows why I have for years said almost every average sized small woodworking shop needs at least a 3 hp cyclone turning a 14" impeller with airflow restrictions and our cyclones should have a real 5 hp motor turning a 15” or 16" diameter impeller.
- Duty Cycle
Now worry duty cycle! After going through all this you still have to account for how hard you are going to use your motor which is known as duty cycle. Induction motors have two main sources of early failure, we burn them up from insufficient cooling, or we break their starting components. It takes a lot of current to start an induction motor, plus we have to change the magnetic field just a little so there is extra pull to get the motor going. We have capacitors to help supply this extra current. To engage these capacitors and change the field for startup there is a motor starting circuit where a spring closes a switch when the motor is off then as a motor comes up to speed a weight pulls the switch open. When starting motors generate far more heat than their cooling fans can get rid of, so if you start your motor too often it will overheat and burn up. Likewise, that starting circuit with weights is one of the weakest links in our induction motors, so the more frequently we start our motors the hotter they get and shorter the lives of their starting circuits. Leeson and Baldor are considered two of the premiere and most respected motor makers in the U.S. if not the world. Both recommend that even their heavy duty compressor motors that come with their best starting circuits not have more than five to six start stop cycles an hour. More than this builds up heat faster than the motor fan can cool so the motors will burn up. Their extra tough starting circuits are why I recommend the use of compressor motors. Compressor motors start slowly because they have a heavy load. Most induction motors can run at maximum amperage full time giving them a duty cycle of 1.0. Some heavy-duty induction motors are rated to run full time at 1.15 times their maximum amperage without overheating giving them a duty cycle of 1.15. Many hobbyist import motors are designed to run at maximum about 80% of the time giving them a duty cycle of only 0.8. You multiply the duty cycle by the working amperage to get a target running amperage, which is what the engineering industry actually uses as amperage. To protect your motor, you need to use your own amp meter and ensure that after changing impellers, changing ducting, opening inlets and opening outlets for the first time that your motor does not draw more than this target amperage or you will burn it up eventually.
- Pressure Blowers
- Ducting Selection
Decide on your ducting size, design, and type. Ducting includes all the pipes, fittings, wyes, T's, hoods, ports, and other items used to carry air (see ducting page).
- Ducting Size
Picking the ducting size is fairly easy and there are a number of cross checks that let us verify what size ducting is appropriate for our single run open at a time ducting system. Our previous blower fan table gave us a blower inlet size that often is the same size that we should use for our ducting. Our fan table showed that most average sized small shops need 6” diameter ducting. We can also use the 800 CFM our requirements table said we need for air volume along with the 4000 FPM airspeed requirement to keep our dust airborne. Using these values in our formula FPM=CFM/Area and after some simple algebra and converting the result from square feet to square inches we end up needing a duct with almost exactly a 6” diameter as the ideal ducting size for most average sized shops.
Although this 6” may be the ideal ducting diameter, very few hobbyist vendors provide anything larger than 4”, so most small shop dust collection systems are configured with the wrong sized duct. That wrong sizing if further reinforced by our tool makers only providing the smaller ports needed for chip collection instead of the better ports and hoods needed for fine dust collection. The 4” ducting and port size does a great job for “chip collection”, but a terrible job when it comes to good fine dust collection. We often confuse our dust collector with a vacuum, when it really needs to be thought more of a water pipe system. Air pulled by a powerful shop vacuum will get pulled around tight corners, through smaller ports, and around obstructions. Because our typical dust collection blowers produce about one tenth as much pressure, air pulled by our dust collection blowers is more like water and will not compress through small openings or squeeze by obstructions. Almost any small pipe, opening, or obstruction can seriously kill our airflow. For instance a typical hobbyist blower that delivers 800 CFM through a 6” duct can only deliver about 550 CFM through a 5” diameter duct and only about 350 CFM when forced to pull the air through a 4” diameter duct. Moving up to the large pipe does not work either unless we also have a big enough blower to keep our mains clear and move the needed volume of air. Jet and Delta have gone with more efficient motors and impellers allowing us to just barely get by with 1.5 hp dust collectors, but otherwise our fan table it tells us that even with our only ducting being a short length of 6” flex hose, we really need a 2 hp blower to get our needed 1000 CFM and keep up the duct airspeed amply to keep our ducting clean. We can also get our 800 CFM by using a much larger blower that costs much more to buy and operate. We can calculate that we need an additional 8.94” of pressure from our blower to overcome the resistance of using 4” diameter ducting. Adding that to our average shop overhead means that to move the same air as a 3 hp motor turning a 15” impeller through 6” duct we need a 5 hp motor turning a 20” diameter impeller pulling through a 4”. Most find it too expensive to buy and run a much larger than needed blower, so eventually choose the larger ducting that will carry the air we need at minimal resistance.
- Ducting Design
Decide on your ducting design. Good ducting design for small shops is really pretty simple, but a lot of engineering and research went into this simple solution. You need smooth straight runs that are as short as possible with the most gradual takeoff and turns that you can make. You also need to have pipes ample to carry our needed air volumes. With air being near incompressible at typical blower pressures, most understand the need to redo our ducting getting rid of excessive fittings, tight angles, plus any hoses or duct with too small diameters to keep the resistance to a minimum.
There is another side to ducting design that frequently gets messed up badly by small shop owners and vendors. Most see larger woodworking shops designed to run every down drop at once then want to use a series of progressively smaller pipes going from the collector down to each machine. Although this all looks pretty and makes for some bragging rights, such systems in small shops really just show that someone does not know what they are doing. As said before air at these pressures is virtually incompressible, so any small down drop, port or obstruction will instantly kill our needed air volume. Since air volume drives airspeed, any difference in size of 2” or more in our small shop ducting diameters kills the air speed we need to keep our ducting mains from building up potentially dangerous dust piles. A system that delivers 800 CFM at 4000 FPM duct speed in a 6” duct can only deliver about 550 CFM at in 5” duct which drops our mains to 2780 FPM. Similarly that 800 CFM becomes only 350 CFM when constricted by 4” duct leaving the main with only 1780 FPM, less than we need to avoid plugging. This means we either use all 6” pipe to match our mains, or we have to open additional gates or put in a hyperbaric dampener that is a weighted trap door that opens to keep the airflow up enough to keep the mains clear. Sadly, often opening that second gate leaves our target machine with too little airflow to provide good collection. Personally, I often just use 6” to everything and split right at the tools into multiple pickups ensuring the cross sectional areas of each ducting pipe adds up to or just over the area of my mains.
- Ducting Type
Decide on your ducting type. Most commercial shops use corrugated steel duct, spiral steel pipe or laser welded smooth walled steel pipe. They have no choice in most areas if they want to pass a fire inspection because ducting fires have long been known to cause serious problems. A well designed ducting system should not develop any piles in the ducting. Unfortunately, corrugated steel and spiral steel pipe are known for rough edges that trap strings, shavings, and chips eventually leading to ducting piles and cleaning issues. The laser welded steel has joints that are nearly as smooth as the rest of the pipe surface, so rarely have these problems. A similar issue occurs with flex hose. Most inexpensive flex hose has very tough ridges that can create up to nine times higher resistance than smooth pipe. Smooth interior walled flex hose is better, but a bit of a misnomer because the inside is still not that smooth having many times the overall resistance of smooth pipe.
Although dust piles can catch on fire, most small shops do not have to worry about reaching industrial dust to air concentrations that can become explosive. Additionally, the physics of dust collection show most small shops never develop enough static charge to ignite a potentially explosive cloud of dust. As a result, many small shop owners not subject to steel ducting requirements choose to use plastic for not only flex hoses, but also for ducting. Many find that PVC 2729 Sewer and Drain (S&D) pipe provides a far less expensive solution than metal pipe. Plastic pipe and flex hose can build up static charges and nobody needs shocked while around sharp fast moving blades, bits and cutters. Regardless, if available in your area the 2729 PVC irrigation drain pipe and fittings cost far less than metal or standard schedule 40 PVC, are much stronger than the metal ducting, don't leak like HVAC pipe, and have a much lower coefficient of friction than even laser welded metal ductwork. The 2729 PVC is rated for many times the pressure that even large industrial blowers generate, but light HVAC duct can be collapsed by our larger dust collector and cyclone blowers. I've seen no flex with my PVC pipe even when doing testing on 10 hp blowers driving a 16" impeller. Another important concern with PVC is static electricity. Forget about the nonsense grounding wire kits for plastic ducting, they do not work well. I share on my ducting page a much better grounding solution, but still think if your area requires grounding your ducting, then you should consider instead using metal pipe. Many very successfully use plastic pipe, but I recommend you evaluate your situation and use pipe safe for your needs. If you use a small blower or a ducting design that builds piles in your duct, you should only use metal pipe to avoid fire dangers because plastic pipe offers no fire protection. Likewise, if you live in cold dry climates where static electricity is a serious problem then grounded metal pipe makes good sense.
Airflow depends upon ducting friction. Here are the Hazen/Williams friction coefficient factors for various duct types (a higher C number is better). All values from Wikipedia except flex hose values that were calculated from flex hose manufacturing static pressure resistance levels. Interestingly, the tighter we pull our smooth walled flex the better the airflow. The looser we string our flex hose the higher the resistance and worse the airflow.
- Corrugated steel duct = 60
- PVC Flex Hose (rough) = 65
- PVC Flex Hose (smooth) = 70
- Spiral Duct = 90-100
- Laser Welded Duct = 110-120
- PVC Duct = 146
Notice that corrugated duct is so restrictive it should never be used! The same is also true of flex hose that has a rough interior. Also notice that in spite of some vendor claims, these values show that PVC flows a lot more air than equal sized spiral metal ducting. Alternatively, you can use either the more expensive but less efficient heavier spiral pipe or the 26 gauge snap lock HVAC pipe.
- Ducting Size
- Filter Selection
Now either blow the fine dust away or buy good quality filters! Ideally blowing the fine dust away outside gets rid of it building up in our shops. Unfortunately, many like me cannot do this so need to filter our air and blow out our shops regularly or after any dusty operations. Regardless, good filtering requires fine filters with enough surface area that they do not clog too quickly and that are protected from being battered and poked full of holes by chips. Again much of the work has been done for us. The medical folks tell us we need 0.5-micron or better rated filters and our air engineers tell us how large these filters must be. Unfortunately, we cannot just buy any filters.
- Filtering Level
With no standards or oversight, hobbyist vendors have been rating their filters themselves often in what I think are back advertising rooms instead of in test labs. Commercial filters get rated by NIOSH or ASHRAE approved independent testing organizations. ASHRAE requires that all indoor filters be tested when clean and brand new. The standard for indoor air quality is use of filters that are certified to collect 99.9% of all particles sized 0.5-microns and larger. Almost no woodworking vendors advertise ASHRAE filtering levels. Instead most small shop vendors advertise filters that are rated when fully seasoned, meaning they have built up as much internal dust as they can carry through a normal automated cleaning cycle. Typical dust collector filter bags provide about 30-micron particle filtering, but this is with the filters fully seasoned. The 30-micron filters make great dust collectors for putting outside because the very open filtering material just lets the fine dust blow away instead of quickly clogging the filters. It can take a year or more for larger filters to fully season, and during that time our filter bags can blow particles right through sized over ten times larger than claimed. Many hobbyist dust collector vendors now provide what they call “fine” filters. I personally measured the filtering of most of the so called "fine" hobbyist vendor supplied filter bags and cartridges in 2001. So did a number of my university professor friends. We found almost all so called hobbyist fine filter bags and cartridges stopped passing air long before reaching claimed filtering level. Those advertised as 5-micron filters freely passed up to 50-micron sized particles until so caked with dust they barely passed air. Most 1 and 2-micron bags freely passed 20 to 30-micron sized particles. Frankly, out of the dozens of filters tested off the leading dust collector and cyclone equipment only Jet, Delta, Powermatic, and Porter Cable provided filters that performed as advertised. My hat is off to them and their employees who stayed honest in spite of marketing losses to other vendors who exaggerate to increase sales. The sub 5-micron hobbyist filters add less resistance, but mostly provide a false sense of security. They make our shops look cleaner, possibly getting rid of the overnight buildup of dust all over everything, but still mostly pass most of the near invisible 2.5-micron and smaller particles known to cause serious long term health problems.
My respiratory doctor recommends those of us with existing conditions should use 0.2-micron filters and always wear a good NIOSH approved mask when doing any dusty woodworking. The 0.2-micron filters are HEPA grade. HEPA grade filters are all rated by an ASHRAE approved independent laboratory assuring clean new filters provide 99.9% separation of at least 0.2-micron sized particles and larger. Further, each real HEPA filter is individually tested and given its own certification number. For Many in the U.S. are now adopting the European standard for which they rate our HEPA as a MERV-16 filter which is what is used for protection from radioactive and biological materials. My doctor recommends those without problems should use at least MERV-14 meaning 1-micron filters, but prefers we use 0.5-micron meaning MERV-15 quality filters. Woodworking creates so much dust that smaller filters quickly clog, but large filters are expensive. Worse, cleaning rapidly destroys fine filters, so our small shop vendors have serious problems. If they provide large enough fine filters they cannot stay cost competitive. That leaves us having to either trust our small shop vendors who have not earned that trust, rely upon outside testing, or buy commercial filters. I personally choose the latter and buy my filters from commercial suppliers. I believe that if commercial facilities in areas that require testing fail to pass an air quality inspection, some heads would roll, so am willing to accept and use filters that get supplied to commercial facilities that must stay in compliance with government standards. Almost always these filters are made from filter material that is fully certified, so can be trusted. I personally will never again trust a hobbyist filter as one of the top magazine rated vendors supplied me fine filters that were so open they badly contaminated my shop and home causing me serious respiratory damage.
- Filter Size
All filters start with some resistance and that resistance grows rapidly as the filters get dirty. The larger the filter area and more open the pores, the longer we can go between filter cleanings. Wood dust is covered with razor sharp edges and very sharp points. Each cleaning cuts and tears our filter pores a little more open reducing their ability to provide good fine filtering. Most commercial dust collection systems use some form of automated shaking or other type of gentle cleaning system. Small shop woodworkers mostly cannot afford the price for such a cleaning system, so are forced to do that cleaning by hand. The cleaning can be a messy dusty shower, so needs to be avoided whenever possible.
Most small shop vendor provided filters have such little surface area that they quickly clog and need cleaning. Clogging kills our airflow we need for good fine dust collection and increases the pressure so high that the finest dust tends to get forced through the filters slowly cutting open the pores so much they no longer do a good job filtering. Although vendors would like us to buy these expensive filters more often, the correct solution is to use larger filters and clean as much fine dust from the air as we can before it gets to our filters. Fine filter material is expensive, so we end up having to make a compromise between filter costs and filter surface area. Cartridge filters accordion fold the filter material in a much smaller space to provide more total surface area. Most cartridge filters have so much more surface area it takes them longer to get dirty. This also reduces how often we need to do filter cleaning, so most small shop woodworkers eventually end up with cartridge type filters.
Unfortunately, most end up with cartridge filtered dust collectors and learn just having lots of filter area is not enough. Cartridge filters get ruined quickly by hits from wood chips, are a constant cleaning nightmare, and often are made too open to do a good job of fine dust collection. Cartridges also tend to be made of thinner material, so clogging more quickly increases the air pressure enough to push the finest dust right through cutting open the pores. That means we need some kind of separator and bigger filters. ASHRAE recommends a minimum of roughly 1 square foot of filter area for every 3 CFM of cleaned airflow when using blended polyester paper cartridges. When using the finer thicker engineered fiber filters like heavy spun bond polyester they recommend a minimum of 1 square foot of filter for every 10 CFM. My testing and years of experience shows we will have far better airflow, significantly reduced filter resistance, and much longer filter life with 1 to 2 CFM for polyester paper blends and 1 to 5 CFM for the man made finer filtering materials. Donaldson Torit is the top name in U.S. large facility filters and they also recommend at least one square foot of fine filter area for every 2 CFM of airflow. They also recommend replacing the fine filters after every three months of full time use. I found that far too expensive, so instead came up with a cyclone that cuts how much fine dust gets to the filters by roughly six fold. Thousands now use my design purchased from Clear Vue Cyclones and they consistently say my cyclone greatly extends filter life and reduces how often the filters need cleaned. I personally started with a pair of 225 square foot fine cartridge filters with one of my cyclones. I later upgraded to using 300 square foot fine filters. My filter pair only adds about 0.25" of static pressure versus over 3” with the prior fine filters they replaced.
- Filtering Level
- Cyclone Separator Selection
Now buy or build a good quality cyclone. With trashcan separators almost instantly emptied of all but larger pieces of wood at the much higher airflow rates needed for fine dust collection, we either buy an expensive commercial staged filter system or use a cyclone to protect our filters. Cyclones are simple tanks with no moving parts and each can be carefully engineered to separate different densities of materials. There are outdoor cyclones next to most large commercial woodworking concerns because these units work well. These outdoor cyclones are engineered to use very high internal turbulence to break apart heavy sawdust and chips from light airborne dust. These units drop the heavy stuff into a bin and blow the light airborne dust away into the outside air. We have excellent engineering modeling programs that let us put in the weight, density, airflow, and separation requirements to design an ideal outdoor cyclone. These programs show for good fine dust separation small shop cyclones should be around 13.5” in diameter and powered by a 7.5 hp motor turning a large 16" or bigger impeller. Many commercial dust collection systems for small shops are just this size and will collect from multiple machines at once. Unfortunately, the engineering programs to configure an indoor cyclone that separates off as much dust as possible are not readily available, so most hobbyist vendors either copy each other or downsize existing commercial units causing all kinds of problems. These outdoor cyclones work great indoors if we use a bigger motor to overcome the high internal turbulence and blow the fine dust away outside, but when downscaled and used with filters most hobbyist cyclones put close to 100% of the finest unhealthy dust right into our filters defeating the whole reason for using a cyclone. Making this problem worse, our hobbyist vendors often arbitrarily chop the cone lengths and change to larger cyclones to permit less expensive shipping, cheaper manufacture, and permit use of smaller blowers. Many of these design changes are unsound leading to poor airflow, bad separation, too little airflow for good chip collection, plugs in our cyclone cones, and even sucking the fine dust right out of the dust bins. Frankly, the situation was so deplorable in 1999 when I first became involved I chose to go back to the basic engineering and design then build my own cyclone. Now six years later in late 2005 it is clear to me that these vendors have not gotten the message. A few cyclone vendors have improved their units with so called "neutral vanes", but only my design and the WoodSucker II use designs that provide good efficient internal airflow and efficient fine particle separation.