Decades of experience show even with good hoods to get good chip collection at most small shop stationary tools we need to move air at close to 4000 feet per minute (FPM) with a volume of about 350 cubic feet per minute (CFM) using at least four inch diameter ducting.
Fine airborne dust is so light even the lightest breath or breeze can blow it around, and woodworking makes so much fine dust that it will be blown all over by our tools and even normal room air currents unless we can collect it as it is made. The experts spent years learning what it takes to capture the fine dust. They found to get good fine dust collection at stationary small shop tools we need to move air at close to 4000 FPM with a volume of no less than 1000 CFM using at least 7 inch diameter ducting.
The experts also found the best ways to get rid of fine dust. Woodworking makes so much fine dust and filters require so much cleaning and expensive replacement that most commercial shops use cyclones or 30-micron filters to separate off the heavier dust then vent the fine dust outside. Fine dust lasts nearly forever when vented inside, but when vented outside it quickly dissipates and breaks down as soon as it gets wet. Unfortunately, it also breaks down into very fine sharp particles of glass and lignin which can irritate, damage and scar our respiratory tissues. Venting outside works very well so long as ample make up air is provided to keep from sucking toxic fumes backward through our vents. Most find they can vent outside and still be comfortable using infrared heat dishes. Air conditioners cannot keep up with the heat losses when venting outside. In some areas venting outside is illegal so filtering is required. The major vendors have found from decades of experience with filters it takes at least one square foot of fine filter area for every 4 CFM of airflow, but to last at least three months with less cleaning most vendors recommend use of twice as much filter area.
Things changed when some peer reviewed medical studies clearly showed all types of fine airborne dust cause many short- and long-term health problems. This new research proved the old standard wrong. Instead of all airborne woodworking dust except Western Red Cedar posing no serious health hazards, all airborne dust causes permanent respiratory tissue damage and permanent loss in respiratory capacity. Further, fine wood dust carries toxic chemicals that can cause death, nerve damage, severe allergic reactions, additional respiratory tissue damage, and worsen age-related diseases. Over the past forty years five different concurrent government air quality standards for airborne wood dust evolved ranging from no more than 15 milligrams per cubic meter to 150 times less. Even more peer reviewed medical studies verified that all forms of fine airborne dust are so unhealthy that the EPA adopted a standard of no more than 0.1-milligrams of fine dust per cubic meter. The EPA now selectively enforces this standard and will site and close office buildings that exceed this 0.1 milligrams per cubic meter of any type airborne dust.
The peer reviewed verified medical research created a monster problem that greatly further confused the dangers of fine dust collection. Woodworking when we include home building affects over half of the U.S. economy. Huge numbers of firms with dusty operations including the government had potentially firm ending liability issues much worse than asbestos. These firms and institutions fought back hard. Insurance companies pulled their Internet data which proved fine dust caused many health problems. Large organizations and vendor associations bought the best studies that money could buy from the most prestigious organizations they could bribe to show there was no harm from fine dust. Our government suppressed access to existing studies and quit funding new studies. You can now find a study to prove just about any fine dust assertion that you want to make unless you need a medical peer reviewed study.
The small shop dust collection vendors cause more confusion because they are in a huge fight to survive. Based on decades of testing I believe that many vendors make up their dust collection and air filtering performance specifications in back advertising rooms. Current magazine testing has forced them to be more honest, but most only advertise maximum air volumes instead of working. Many also use tricks to increase the tested maximum air volumes and this runs their motors well over capacity. Most motors are tough and can run long enough for testing, but in the last test I oversaw five vendor motors burned up during testing. The sad part of this is the magazine tests did not cut off each test as soon as the motors were at maximum amps. The result is the magazines promoted dust collector and cyclone vendors as top picks that in real use are only marginal performers. Many also cheat and advertise outdoor filter performance instead of indoor. Indoor filters must be tested when clean and new. Outdoor filters are tested after they have built up internal dust stuck in the filters that does not come out with normal filter shaking or air blast cleaning. These particles trapped in the filter matrix improve filtering roughly tenfold. As a result, most firms that are advertising good fine dust filters that they claim filter down to 1-micron are really selling 10-micron filters that provide no health protection because they blow the unhealthiest invisible dust right through.
Finally, woodworking to a huge degree is a craft passed down by our experts. Most woodworking experts have years of experience and know exactly what they are doing and can share well. As a result, we put considerable trust in them even when they give dust collection advice which is often wrong. One day I got a long email from one of the best-known woodworkers who had multiple TV shows. He wanted me to forgive him. He not only declined my efforts to contact him, he totally ignored the long paper I sent him that showed why his so-called best dust collection system was going to hurt him. I had exactly the same system and my working fairly toxic wood with that system landed me in the hospital with a severe allergic reaction. That system had too little airflow for good fine dust collection and a filter that freely passed all the unhealthiest dust right through. He shared in confidence that he wished he had believed me because his health failed from too much wood dust exposure and he had to cancel his shows. He now can only make guest appearances and cannot do any real woodworking that creates dust. He said this was still my fault because I did not kick him hard enough to get his attention and convince him to stop blindly following his mentors when it came to fine dust collection. The bottom line here is most woodworking experts give widely varying advice because what seems logical mostly does not work when it comes to fine dust collection.
No wonder dust collection is confusing. There is an overwhelming amount of contradictory information from our government, trusted institutions, vendors, magazines and even expert woodworkers.
Sorting out all of the overwhelming mass of confusion is impossible, but the reality is very simple. We use dust collection to protect our health and keep our working surfaces clear so we can better see and handle our work. In spite of the confusion dust collection really breaks down to chip collection that collects the visible dust and chips, and fine dust collection which keeps the dust levels in our shop air below the maximums. There are many firms who build custom dust collection systems and guarantee customer air quality. They share their decades of experience and engineering that show just what is needed in terms of upgrading hoods and required airflows. Since small shop stationary tools are the same as smaller commercial tools, most of what they share is also accurate for small shops.
Many areas have required traditional dust collection since the 1920s, so what is required is well understood and documented. The smaller commercial stationary tools all require hoods that effectively direct the dust filled air streams and 4-inch diameter ducting carrying 350 CFM airflow to provide good chip collection. Most recommend using grounded metal ducting to transport the airborne dust as the metal is required by almost all fire safety inspectors and insurance inspectors. Still, many have found plastic duct to work better. I personally had to use grounded metal tape inside and out of my plastic duct to ground it as it gave me terrible shocks in cold dry weather. We also must maintain a ducting air speed of at least 4000 feet per minute (FPM) in vertical duct runs and 2800 FPM in horizontal to keep the dust from settling and creating piles in our ducting. Duct piles pose a very serious fire risk, plus when they break loose, they can blow apart our ducting joints and ruin fine filters.
Good fine dust collection is not much more difficult. We have to have better hoods that control all of the fast-moving air streams and direct them for collection. We need to know that woodworking creates so much fine dust, we have to capture almost all of it, or our shops will make it unhealthy to breathe without a good respirator mask. Most small shops will exceed the EPA airborne dust limits when hand sawing just over 7 inches of a ¾ inch board. We must maintain at least 50 FPM air speed all around the working areas of our tools to over 15.25" to pull in almost all of the fine dust before it escapes. Once the dust escapes it can take hours for an air cleaner to bring the dust levels back down to safe. Those vendors who guarantee customer air quality say that it takes 1002 CFM and both our testing and working the math backward verifies this same figure. Just like we rounded the 349 CFM needed for chip collection we will round the 1002 CFM to 1000 CFM as the minimum for good fine dust collection. This means the same machines that get good chip collection with 350 CFM require 1000 CFM for good fine dust collection.
Many go crazy when they hear that their systems which can lift a bowling ball cannot pull in the fine dust we can move with the lightest of breaths. The reason is simple. Sucked air comes from every direction at once. Air is governed by the formula FPM = CFM / Area where area is measured in square feet. With sucked air the air speed drops at a rate of the initial speed divided by a sphere with that same distance. In English both the formulas and testing verify that the airflow falls off too fast to pull in the fine dust without a volume of at least 1000 CFM.
I was badly blindsided after installing the top small shop magazine rated cyclone dust collection system. It was advertised to provide good health protection and provide ample airflow to collect from three large and one small tool working at once. My vendor sized and configured my system, designed my ducting plan, provided their ducting and supplied their best fine filter. This cyclone collected far worse than my prior cyclones and much smaller dust collector, plus it required me to spend more time clearing its clogged filter and cyclone cone than doing woodworking. Each cleaning left me and my shop covered in the dust I installed this unit to avoid. Thinking it at least protected my health I foolishly continued to use it to finish my Christmas projects and planned on replacing it with a commercial system in a few weeks. Instead, less than three months after installing that system I was rushed to the hospital with an apparent heart attack. My doctors found in just a few months I went from no allergy problems to such bad allergies that my lungs would not supply enough oxygen for my heart. This made no sense because recent allergy tests showed no problems, I used the best finest filters available, and consistently wore my fitted dual cartridge respirator mask when doing dusty work because no dust collection system can capture all the fine dust. Allergy tests confirmed with nasty welts and boils severe allergic reactions to a wide range of woods, many of which I never used. My respiratory doctor a fellow woodworker, said he has seen many develop bad allergies to cocobolo and rosewood in as little as a few hour exposure.
My health did not improve and the allergic reactions continued so my respiratory doctor asked me to pay for expensive air quality testing to see if my shop and home were contaminated. I stalled not believing him. My shop should have been clear as no woodworking had been done for months and during that time our cars that share the garage were constantly going in and out, plus I blew all out with my electric leaf blower. The shop had to be well aired out and clean. My home had a very expensive upgraded fine dust collection system built into the HVAC, so it should have gotten rid of the fine dust. After three months of not getting better I paid for expensive testing. My certified inspector gave me quite an education and shared the detail of what the major vendors found it takes for good fine dust collection, as follows.
Inspector: I called in a huge favor and got my inspector who was the senior OSHA inspector for our area who had tested hundreds of shops. He said my shop was one of the cleanest he had ever seen, but then predicted my shop and home would both badly fail. He explained that I installed the same system that most buy before going pro and all have the same problems with their cyclone failing all the way around.
Fire Safety: My inspector said my indoor dust collection system was not certified as fire and explosion proof so unless it was placed outside behind a fire and explosion proof barrier it would fail building, fire marshal and home insurance inspections. He shared that most shop fires occur because a spark gets into the collection bin then smolders to later grow into a fire, often long after we have left our shops, so my system's cardboard collection bin was a fire just waiting to happen as were the plastic bag below my older dust collector and plastic tub below my shop vacuum. He said my impressive graduated sized ducting system was dead wrong for a small shop that only collected from one tool running at a time. Duct size determines air volume and speed, so my smaller down drops so limited the airflow that my mains would build up piles. That explained why piles kept forming in my mains and when I opened up larger down drop blast gates these piles would slam down the pipes so hard they blew the joints apart and destroyed fine filters. He said I should look for a You Tube video shot in the dark while cutting on a table saw. This video show some woods throw off sparks similar to grinding steel, He shared that if a spark lands in a duct pile it can quickly be blown into a nasty ducting fire. My only choice was to completely redesign my ducting. Trying to run my system with multiple gates open created enough airflow to avoid the piles but left too little air to even get good chip collection let alone good fine dust collection.
Proper Design: He said my vendor's advertising claims promising good fine dust collection from three large tools and one small tool working at once were nonsense. He said he tested many shops with this vendor's dust collection systems and none passed air quality tests. He explained that the experts who guarantee customer air quality found the only way to get good fine dust collection is to collect the fine dust at each source as it is made which requires upgraded hoods and much higher airflow. This vendor's designs fail to move enough air for good chip collection, let alone good fine dust collection, plus they use wide open filters that freely pass the unhealthiest fine invisible dust. I explained that my system used the much more expensive upgraded finest filters. He said this is a common lie as vendors can claim any level of filtering they want unless they share that they test when the filters are clean and new. Even a road grate becomes an excellent fine filter if clogged enough that it no longer passes air. His particle counter proved my expensive upgraded fine filters freely passed the unhealthiest fine invisible dust. He looked at my expensive air cleaner and showed with his particle counter that it also freely passed the unhealthiest invisible dust, so was great for protecting finishes but useless for good health protection. He said even if I had good fine filters on both my cyclone and air cleaner, woodworking makes so much fine airborne dust and it spreads so rapidly that there is no chance that running both would get rid of enough airborne dust fast enough to avoid failing air quality tests. Airborne wood dust spreads so quickly that each time our cleaner or exhaust fan moves a shop full of air, it only collects less than half the airborne fine dust. This is why my air cleaner required hours to clear the dust, but my big fan only needed about thirty minutes. Clearing the air would be far too slow to protect my health and avoid contaminating my shop and attached home.
Proper Hoods: He said most dust collectors are optimized to move air at 4000 feet per minute (FPM) which is a little over 40 miles per hour. Most of our blades, bits, cutters, and sandpaper launch fine dust filled air streams at over 100 miles an hour, so we must start with upgraded hoods that contain, direct and enable capturing the fast moving air streams or there is no hope of good fine dust collection. None of my tools had the upgraded hoods required.
Dust Riddance: He explained the problem in my shop would be very bad. I vented inside so the fugitive dust that escaped collection would build to dangerously unhealthy levels. He said most large facilities choose to vent outside. Not only does all dust collection equipment have to be either fire and explosion certified or placed outside behind fire and explosion proof barriers, but also almost none choose to filter because filters constantly need cleaned, are expensive and typically need replaced every three months. Most large facilities find that venting outside is the most efficient, safest and least expensive way to get rid of the fine invisible unhealthiest fugitive dust that escapes collection.
Inspection: His gauges showed just walking around before doing any woodworking stirred up enough invisible dust to cause my shop to fail its air quality test. As soon as we turned on my cyclone without any woodworking my filter was such a dust store it blew so much fine dust all over that the air quality got five times worse. My system collected so poorly a few minutes of woodworking pushed the airborne dust level to 15 milligrams per cubic meter which is as high as normal room air can carry. He said the fugitive dust that escapes collection builds so much that government testing shows in most small shops, including hobbyist shops, if we vent inside we get more fine dust exposure in two hours than most large facility wood workers get in months of full time work. His meters also showed my home badly contaminated and a chemical test showed the main contaminate was wood dust. He explained woodworking makes huge amounts of fine invisible dust, this dust is so light it behaves more like an odor so will rapidly contaminate any shared air space and this wood dust lasts nearly forever unless it gets wet. Going through the door that connects my garage shop to my home let the contaminated air into my home, plus I carried in more fine dust in on my hair, skin and clothes. His test gear showed even my fine home air filters freely passed the fine wood dust, so like my shop that kept recirculating the air, the contamination just continued to build with whatever more came in.
Ample Airflow: He said most of the 3 hp and smaller dust collectors and 5 hp or smaller cyclone systems move enough air for good fine dust collection. He reiterated that chip collection collects the same visible sawdust and chips that we would otherwise sweep up with a broom and has been a requirement in some areas since the 1920s, so is well understood and documented. Good chip collection requires a real airflow at most small shop stationary tools of 350 cubic feet per minute (CFM). Likewise, good fine dust collection has been a requirement in some areas since the 1960s so is also well understood and documented. Good fine dust collection keeps the amount of airborne dust below EPA maximums. Fine dust that can be blown around with the least breath will get blown all over our shops unless we have hoods to control the fast moving air streams, move enough air to surround the working areas of our tools and pull in the fine dust before it gets blown all over by normal room air currents. It takes moving a full 1000 CFM to pull in the fine dust on the same tools that get good chip collection with 350 CFM. His test gauges showed even when collecting from just one tool at a time the airflows my system provided ranged from 30 CFM to less than 350 CFM regardless of my vendor advertising 1200 CFM maximum airflow. He explained most vendors cheat and publish maximum airflows which are measured without any ducting, no filters and often oversized blower inlets and special bell shaped hoods that increase airflow, so maximum advertised airflows tends to be over double working airflows. My vendor made all worse by using all four inch diameter down drops and smaller when they needed all seven inch diameter down drops to carry the 1000 CFM needed for good fine dust collection. The small ducting limited the airflow far below what it took to keep the dust and chips moving in my ducts. Worse, instead of going up before going down, my down drops all went down from the mains. This caused the dust to fall in all downstream down drops leaving them full of dust or plugged. It moved far less when trying to collect from more than one tool at a time.
Fine Dust Definition
Fine Dust Sources
Our testing confirmed most small shop vendors sell equipment not based on how well it works, but instead on what it takes to be cost competitive. There are no standards or oversight on small shop equipment makers except what we choose to buy. Making informed choices is tough because most available advertising information is misleading. All vendors cite maximum airflows, but working airflows are consistently only about half maximums. Many vendors lie. Our truth in advertising laws permit vendors to say anything they can prove for an instant. For instance, I can claim my car gets 99.9 miles per gallon because my mileage gauge shows this reading when coasting down a steep hill. With filters so long as the vendor does not include flow, they can claim anything they want. Even a chicken wire screen with 1” openings when clogged enough will eventually become a 0.3-micron filter with almost no airflow. This is why ASHRAE who sets the filter standards requires that all indoor filters be tested when clean and new and measure both airflow and filtering.
Fine Dust Lifetime
Fine Dust Behavior
Fine Dust Health Risks
Wood Dust Health Risks
Wood Dust Volumes
General and Sawdust Safety
- You need to start by learning how to safely use your tools. Many blades, bits, cutters and sanders that can quickly go through tough wood can do far worse to our bodies if we don't learn how to use all of our tools. The basics of safely using tools prior to the 1970s was required in most area for all males and optional for females. If you use your tools unsafely or force them the odds are 100% that they will eventually hurt you, potentially badly, especially your hand tools. Please take good safety course and always follow good safety rules.
- Sawdust, chips and debris left on our floors and work surfaces pose significant risks including slipping, falling, and sliding into moving blades, bits, cutters, and sanders. Nearly all eventually have sawdust related accidents in their shop. Slipping into a moving blade, bit cutter, or moving sanding surface can cause devastating injury. Sawdust on our work surfaces and tools can cause work to not fit snug up to our fences causing cuts that are too short or have a slight unwanted bevel. Sawdust also obscures our layout and cut lines leading to wasted time and materials. A broom and dust pan will clean up the sawdust, but most wait too long, so it is far safer and more convenient to have a good dust collection system that captures the sawdust and chips as they are made. This is why many areas have required good chip collection since the 1920s and you should use good dust collection in your shop.
- Sawdust, chips, cutoffs, paints, stains, fillers, solvents, adhesives, liquid propane and many other things used in our shops are flammable. Most shops have many sources that cause the flammable things to burn. Our blades, bits and cutters make lots of sparks, particularly when we burn wood while cutting or sanding. Many tools have cases that surround the motors and so much dust can build up that the motors loose cooling and catch the built up dust on fire. Also many hand tools throw off sparks from their brushes. These sparks can trigger a fire on our floors, in our dust bins, and even in our ducting that can burn down our shops. Electric heaters can also ignite dust. Many vendors often offer felt filters, cardboard bins or plastic bags for dust collection which will not contain a fire. We also get fires from spontaneous combustion when stored wood dust or oil-and-paint soaked rags build up too much heat. Fire and insurance inspectors require good dust collection that keeps our floors, work surfaces, and tool cabinets clean. They also require use of metal ducting, heavy metal dust bins and heavy metal fire proof rag containers that can force a fire to smother itself. They require all of the other flammable materials to be stored in a metal storage locker that is fire proof. You also do not want the fumes from these materials to ignite, so should work in a well ventilated area. You need to equip your shop with at least one fire extinguisher and should also use a fire alarm in your shop that is paired with at least one in your home so all go off if any are activated. It is also useful to use a carbon monoxide detector close to your shop floor.
- Smoking in and around woodshops is illegal for larger government monitored facilities because it is too easy to suck up and leave burning material in our dust bins that may smolder for hours then burst into flames long after we leave our shops.
- Most do not know is the risk of having a fire that totally burns down your shop are just under 2% but during you life most woodworkers will have multiple shop fires that ruin equipment and part of the structure. Most of these fires are traced back to using plastic, cardboard, and felt dust container that pick up a spark or hot ember, smolder until long after leaving the shop, then burst into fire. The next most common is from spontaneous combustion from wood dust or solvent or oil covered rags that get so hot they burst into flame often long after we have left our shops. Next are fires from paints and other flammable materials. With a 100% chance of problems eventually, it is well worth taking good precautions against fires.
- Fine airborne sawdust can burn so rapidly it creates an explosion. Most dust explosions occur when a large cloud of sawdust is released next to a source of ignition like a large electric spark, a spark from metal working, or the burner in an electric heater or heat disk. This problem is so bad and frequent in larger commercial shops that almost all U.S. fire codes require all to only use good dust collection that precludes releasing dust clouds into shop air.
- We also get dangerously high amounts of airborne dust when sucking up large amounts of dust from our tools, floors, that is trapped in our machine cabinets, or large piles of dust trapped in our ducting. This dust will explode when it gets a source of ignition, often a powerful static electricity spark in our ducts. This is why fire inspections require that all dust collection systems either be UL approved as fire and explosion proof and come with an explosion port that will direct any explosion safely away otherwise, all must be put outside behind a fire and explosion proof barrier. Few small shops have dust explosions because we rarely create dangerous amounts of airborne dust or generate big enough sparks to trigger a fire or explosion. To minimize our risk in small shops we should ensure we always have the needed airflow to keep our ducting clear of building up any piles, limit how much fine dust our systems take in at once and ensure we have no sources of ignition.
Fine Dust Safety
- Woodworking and other dusty operations are going to make huge amounts of fugitive dust which is dust that escapes collection. Most fugitive dust is the unhealthiest fine dust which is invisible without magnification. This invisible unhealthy fine dust will stay airborne in normal room air currents then settles often overnight only to be launched airborne again and again as soon as we stir our shop air.
- Because we cannot always collect the fine dust, we should always wear a good NIOSH approved dual cartridge filtered mask whenever we make fine dust and must continue to wear that mask until our shop is well blown out. I recommend the 3M 7500 series masks fit properly to not leak. I personally also use this mask with 3M organic vapor cartridges with their special pre-filters. You should keep your organic filters (or whole mask) in a zip lock freezer back that you suck all the air out of before sealing. This slows the activated charcoal in the filters working much longer.
- The best way to keep your shop cleaned out of the fine dust is to always work with a good industrial 30” or bigger fan blowing out a side door or window with an opposite door or window open when you are making fine dust. It is best to keep that fan on while you work. My test meters showed most small shops need thirty minutes to get the shop air cleared well enough to take off your mask and turn off your fan. The fan keeps the fine invisible dust from building and creating a bad residual dust problem. I also clean my shop by having the doors open with the big fan blowing and use a leaf blower to move all the dust out.
- Avoid tracking dust into your home, office and vehicle, plus always blow yourself off well and wash up before leaving your shop. It is easier to control the dust if you wear a good long apron that you leave in the shop. When doing really dusty things, also wear a smock, scarf and hat. All need blown off after use.
- I recommend those that work in shops or garages that attach to our homes also install a simple bathroom vent fan in your shop that vents outside. It should turn on when we turn on the lights. This vent fan creates low pressure that keeps the home air going into the shop instead of the dusty air rushing into our homes whenever we open a connecting door.
- When it would be inconvenient to use my cyclone I put on my dust mask and turn on a large commercial fan that vents my shop, then use my Jet 1.5 dust collector with its upgraded fine filter to collect the visible sawdust.
- Good fine dust collection starts with good chip collection. Good chip collection requires about 350 CFM air volume at most small shop stationary tools. We need to move air at a speed of about 4000 FPM to collect the sawdust and chips plus keep our vertical ducts from plugging. We also need to maintain at least 2800 FPM airspeed in our horizontal ducts to keep them from building up piles. Dust piles in ducts pose a serious fire hazard. When these piles break loose they can slam down our duct to blow apart joints and expensive filters, plus these piles when they break loose can create a potentially explosive dust to air mixture.
- As discussed previously these powerful systems that can pick up heavy tools are not enough for good fine dust collection. It takes a lot more air to provide good fine dust collection than chip collection. The top experts who guarantee customer air quality found most small shop stationary tools that get good chip collection with 350 CFM need about 1000 CFM to get good fine dust collection. The testing shows we must move at least 50 FPM out to over 15.26" all around the working area of our tools to pull in the fine dust before normal room air currents can disperse it. Building this big bubble requires moving lots air, specifically 1002 CFM which we round to 1000 CFM. This is just about three times more than what we need to just collect the heavier sawdust and chips. Plus when we upgrade our ducts amply to carry enough air few dust collections systems produce the pressure needed to avoid plugging and get good collection. We still must maintain ducting air speeds of at least 4000 FPM in vertical runs and collection points like hoods, plus at least 2800 FPM in horizontal runs to get good collection and avoid plugging.
- Experts found long ago that woodworking makes so much fine dust and it spreads so quickly that air cleaners and exhaust fans have zero chance of clearing the air fast enough to provide good protection or avoid failing an air quality test. It takes a long time to clear dusty air as most tools put tens of thousands of times more dust airborne than is safe. Dust spreads so quickly that even after replacing all the air in our shops we have collected less than half the dust. So, the only way to provide enough collection to maintain good air quality is to collect the fine dust as it gets made before it has a chance to spread.
- Unlike compressed air or air pulled by a vacuum cleaner, the low pressure air used for dust collection will barely compress at all. Any small hose, small tool port, or sharp bend in our ducting or hoses will kill our airflow just like partially closing a water valve. At typical dust collection blower pressures a 4" duct will only support about 350 CFM, a 5" only 545 CFM, a 6" only 785 CFM, and a 7" only 1069 CFM. This means typical dust collectors and cyclone systems need at all 7” diameter or larger flex hose and ducting to move the required 1000 CFM for good fine dust collection from most stationary tools. What I do for my cyclone designs and Clear Vue is use an over sized blower which generates about 12” of pressure. This permits me to get a real 1000 CFM through a 6” duct. Caution, using a blower that moves too little air will result in piles forming in your ducting which can fill down drops and create dust piles which can cause fires and destroy our duct joints and filters when these piles break loose.
- Good fine dust collection must start by upgrading tool hoods to block and trap all the fast moving dust laden air streams. The reason is simple. Most dust collection systems move air at around 40 miles an hour but our blades, bits, cutters, and even sandpaper launch dust filled air streams at over 100 miles an hour. Our dust collection systems cannot keep up, so we need good hoods to contain, control, and deliver these fast moving dust filled air streams for collection. My ducting page shares many good hood solutions.
- The experts show most tools also need either a larger port or an extra port. Almost all current tools are setup to move about 350 CFM which only requires a 4" port to pass enough air to collect the heavier sawdust and chips. To fix my band saw it required adding a 5” port under the blade and a 4” pickup port over the blade. Likewise, my table saw needed adding a much better blade guard with a 4" port plus upgrading the 4" port on the saw cabinet to 5".
- Picking the right kind of blower is easy. Depending on shop size our blowers must overcome 5" to 12" of resistance between our hoods, ducting, filters and filter loading. A typical squirrel cage blower does not work because they only generate about ½” of pressure so we get almost no airflow. Shop vacuums generate over 60" of pressure but even the largest rarely move over 250 CFM which is too little air to pull in all of the fine dust before it escapes. Airfoil and caged blowers move enough air, but their impellers (fan blades) cannot tolerate material hits from knots, chunks, hardware, etc. and their impellers build up debris which can throw the impellers so badly out of balance they destroy motor bearings. Airfoil blowers cannot provide enough pressure without the blades stalling which causes chatter that also ruins motor bearings. So, we must use a material handling blower just like is used with almost every dust collector and cyclone separator.
- Our material handling blower must move at least 1000 CFM with at least 5" to 12" of pressure to overcome the resistance of our hoods, flex hoses, ducting, filters and the dust that builds on and blocks our filters. Blower technology is mature meaning blowers of the same types and speeds from the professional blower firms all perform near identically. Sadly, most of the less expensive import blowers found on small shop dust collectors and cyclones are not nearly as well made so tend to move much less air. The bottom line is most dust collectors with 3 hp or smaller motors or cyclone systems with 5 hp and smaller motors will move enough air. The cyclone blower needs to be bigger to power the air also having to spin in a tight separation spiral inside the cyclone. Using smaller blowers may pickup the visible sawdust but will not do a good job on collecting the fine dust.
- The experts who guarantee air quality found the best way to deal with the collected fine dust is to separate off the larger particles then simply blow the remaining fine dust outside. Fine dust will last forever if kept dry, but almost any moisture causes it to quickly breakdown. Use of infrared heat dishes deals with the heat loss from venting outside in even the coldest climates, but in hot areas and in areas where you cannot vent outside, you then need to air condition and filter. Likewise, many like me live in areas where it is illegal to vent outside, so we must filter.
- If you must filter then you should use a good cyclone separator that keeps the dust and chips out of our filters. Chips will jam and punch holes in our the filter pleats which can ruin our filters, especially when cleaning. Most cyclones do not at all separate all the airborne dust particles which include all the fine dust particle and larger particles up to about 30-microns which is triple the size of large fine dust particles. As a result, almost all cyclones ruin fine filters quickly, because they do not provide good separation.
- Please be very cautious about vendor performance claims. Most vendors use their cyclones to first collect a big pile of dust and chips, then empty that collected stuff and suck it back up again. With fully seasoned fine filters as well, they still only get a 98% separation efficiency. Of course these claims are pure fraud. The first pass gets rid of all the airborne and fine dust which makes up about 15% of the total weight of the dust produced. They also avoid having to collect almost all the long strings and fluffy chips that make up another roughly 2.5% more of the debris produced. These items normally get stuck in our filter pleats with that first pass. So most only collect 17.5% which becomes 19.5% when we note their second pass only collects 98% of the dust by weight. When my test team tested the previous top magazine rated cyclone with calibrated airborne test none of their system collected the fine dust and most put the rest of the airborne dust into the filters. At these filter loadings paper fabric filters need cleaned roughly every two hours of woodworking and need replaced every three months. The much heavier polyester filters work better in that we only need half as much filter material to get the same filtering. Unfortunately, with half the area they clog in half the time, so most during our tests clogged in about an hour of woodworking.
- Frustrated by the high cost of fine filters, need for constant cleaning, and short filter life I designed a much more efficient cyclone that Clear Vue sells separates the airborne dust six times better so most can go months between filter cleanings and the filters last years. Clear Vue Cyclones licensed my design and now makes these units in metal or a clear tough plastic, the same stuff used to make police shields. My area makes venting outside illegal, so vent my 1200 CFM cyclone into a pair of “200” square foot cartridge “nano” filters I bought from Wynn Environmental.
- I also made my own air cleaner using an 8” in line duct fan that produces nearly 800 CFM. That fan sits on weather stripping on a third “nano” filter. My gauges show it takes about 3 hours of that air cleaner running to pull the dust level down in my large home to what is considered medically safe even on the smoggiest days.