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There are few topics that get as many arguments on woodworking forums, and as strong but conflicting answers, as the issue of dust collection. Perhaps it is because it isn't fun... it may cost more than a new table saw, but isn't fun to buy or operate. It doesn't "show" in the work you create. But it may save your life.
Bill Pentz is an engineering professor and woodworker who has done a lot of study of dust collection. (It began when he was hospitalized a decade ago, with loss of half his lung function, after installing a dust collector that left his shop looking clean, but with huge levels of harmful but invisible dust.) In many respects, he is the ultimate expert, but his answers are detailed (more information than we want to know, and often not what we want to hear), but I strongly recommend his web site, www.billpentz.com. Any time my information differs from Bill's, assume he is right. And since he has invested a fortune in dust collector research, consider contributing to his effort. But I am going to continue writing to hopefully get people started along the right path.
As many authors do, I am dividing the world into three categories, including woodshop dust.
Why do I need a dust collector? I have a shop vacuum, and it cleans up my shop pretty well. Sure, it collects the chips, and may even collect the larger dust particles. Most shop vacuums have to work after the dust has settled... they do not move the volume of air to keep up with the chips and dust produced by our power tools. To keep the air moving fast with a small (noisy) motor, the airflow cannot be constrained by a "heavy" filter. The "easy" filter does not constrain the airflow, also lets the fine (and maybe medium size) dust pass, and blows it back into the room. Health-wise, you are probably worse off than you were with a messy shop.
An "under $100" accessory has been invented for shop vacs. It is a cyclone that takes most of the chips and dust out of the airflow before it gets to the shop vacuum. Then the filter in the shop vac stays relatively clean, and operates at high efficiency, without spending lots of time cleaning the filter or vacuum. The number of examples are growing rapidly, including the Dust Deputy Vortex from Oneida, and others. They are a great idea for improving the shop vacuum, but don't replace a dust collector connected directly to dust-producing machines. They are good at clean-up of large and medium dust, but are not generally good at capturing the really fine dust. Some of the shop vacs have expensive HEPA filters that collect the harmful fine dust, but using the disposable HEPA filters for every day cleaning becomes expensive - the add-on cyclone approach may dramatically extend the life of the HEPA filter bags, making this a good approach. (My speculation, since I don't know how long the HEPA filters will last if they have to collect ONLY fine dust.)
Yes, I am guilty. I couldn't bear the thought of spending enough to get a cyclone, so I bought a conventional dust collector. The kind with a couple bags.
The original system had a very good airflow, but I finally figured out why... the bags collected chips but let the dust back out - the airflow was not being filtered clean by the bags. The corner of the shop with the dust collector was being caked with a layer of dust. And with a lot of dust that I could see, it was also mixing the fine dust (that I couldn't see) into the air for me to breathe.
The first fix was to get 0.3 micron bags. The vendor insisted that I wouldn't have enough airflow unless I had those bags on both the top and bottom, so I installed two. System worked great for a few minutes, but then the bags plugged. The chips and dust embedded in the lower bag, and fine dust plugged the upper bag. Lets see, woodworking for 15 minutes, then 30 minutes with a shop vac, working in a cloud of dust, trying to clean the bags enough so that they could be used again for another 10-15 minutes. Didn't make sense.
The internet forums suggested that I talk to American Fabric Filter - AFF - they make bags that are more efficient... but they are large. The custom bag they made for my 2 hp collector is about 3 feet in diameter, and reaches my 10 foot ceiling. The bottom bag could be plastic - the air would exit through the top bag, and the accumulated chips and dust from the top would drop in the bottom bag. The performance of the large felt-like bag depends on the "cake" of fine dust on the inside of the bag, providing the fine filtering. Therefore a big bag is required to provide adequate air flow through the cake and felt. It was a big improvement, but not the final answer.
Another solution looked good, but I haven't tried... a cartridge filter "on the top." The pleated paper filter has a fairly large area, so may start out like my giant fabric filter, but can be damaged by the chips, and can be plugged like any other filter. A bar is often included, to knock the dust off the pleats inside the filter, but that puts substantial wear on the relatively expensive filter cartridge. Breaking news - if a baffle is installed to keep the chips away from the cartridge, like the Thein separator described below, that helps the life of the cartridge. I also learned that banging the top of the cartridge, where there are no pleats, may jar more grunge out of the filter than the paddle some systems provide to bang on the inside of the cartridge pleats.
A couple other problems with a single stage collector. First, the dust and chips go through the fan. Better hope you don't pick up a nail or screw (and certainly don't use the optional "floor sweep"), because that metal piece can cause a spark when it is hit by the fan, and that spark can smolder in the dust for hours before catching fire in the middle of the night. Second, the air and grunge are blown into the filters before they drop... so chips and other material will wear or damage the filters.
This is sometimes called a two stage dust collector. A high volume of fast moving air can carry heavy chips in addition to fine dust. Air from the machines is spun around a funnel-like "Cyclone", and as the air spins around and down the gradually narrower tube, it slows, dropping the dust and chips into a bin below (the first stage). With a perfect cyclone, the air stops at the instant it changes direction from around and down, to being sucked up the center, through the fan, and out. If it stops completely, all the dust is dropped. If it just slows, the chips plus most of the dust is dropped. If there is an air leak at the bottom of the cyclone (often at the seal of the trash bin) the airflow is disturbed and a lot of dust remains in the air. Note that normally most of the debris is gone before it goes through the fan and into the filter. The filter after the fan is typically a large, very fine filter, often a pleated cartridge (the second stage). However, with little dust left in the airflow, there is little contamination of the filters, so the filters remain very efficient. (If you have a cyclone and the filter gets plugged frequently, something is wrong with your setup - likely an air leak at the collection bin, or you should contact the vendor.)
There are huge battles about different types of cyclones. Almost any circular container will drop the chips and "look good" but a slight turbulence in the air from a less than perfect shape or air leak, and the efficiency plummets - the fine dust is not dropped. The fairly tall cyclones that do the best job of dropping dust and chips don't fit within the typical small shop ceiling. Shorter cyclones either require much higher power or become less efficient - don't separate the dangerous fine dust.
Bill Pentz designed a cyclone for optimum performance and published the plans on his web site to allow woodworkers to freely (no royalty) build one for their personal, non commercial, use. Parts of the design were stolen by vendors (who didn't pay design royalties required for commercial use), and other parts should have been stolen - Bill can demonstrate that many of the highly regarded cyclones aren't very good at separating the very fine (dangerous but invisible) dust. Experts (who are not trying to sell a competing product) generally agree that Bill's design is excellent. ClearVue Cyclones is the only vendor currently licensed to use Bill's design in a commercially available cyclone. The ClearVue founder, Ed Morgano, retired, and when he stopped taking orders on May 1, 2010, I feared the death of a good company. A couple months later (July 2010) it was bought by Bushey Enterprises, three brothers, who moved the manufacturing to Seattle, with office operations in Burlington Vermont. In August 2013 manufacturing is moving back to South Carolina. Wherever they are, the business is continuing.
What cyclone to buy? I have heard at least as many bad comments as good about JDS dust collectors. Penn State Industries sells the Tempest dust collectors, but they don't design and build them. Grizzly specs look good, but the user enthusiasm on the woodworking forums is not convincing - Grizzly cyclone users are happy but far less enthusiastic than users of some of the other Grizzly machines. Shop Fox is a close corporate relative of Grizzly. ClearVue user reviews are always positive. Oneida seems to have good user reviews. All these notes are based on second-hand discussions, not on first person experience. I helped a friend with a commercial shop select and install an Oneida system. For my own use my evaluation focused on ClearVue and Oneida, and ultimately I installed a ClearVue.
| The battle of the Titans | |
|---|---|
| Bill Pentz | Oneida Air |
On June 21, 2010, I got an Email from Bill Pentz. He was very complementary about this web page until I got to the point of recommending Oneida. Bill said "Please rethink that recommendation. I think the Oneida Air System cyclones are probably the worst choice that someone can make today due to terrible separation, poor filtering and way too little airflow in all but their 5 hp and larger units." |
On September 16, 2011, I got an Email from Lisa Barone of Oneida Air Systems. She was very complementary about this web page and the need for dust collection at the source. She goes on to say "I am sorry to see that you have given a forum to Bill Pentz and his anti-Oneida rhetoric. I would ask that you remove his negative comments and understand that he has no foundation for them." |
Trying to understand the battle, I have done some more research... back in the late 1990s Bill Pentz, an engineering professor and hobby woodworker, bought a cyclone to keep his shop clean. Despite the clean appearance, he ended up hospitalized with lung and heart damage that was traced to shop dust, bad enough to require full time oxygen. As a professor he started researching the problem (as a one-time professor, I know that is a very natural thing to do). He became an expert and found most commercial designs didn't hit the target. He offered consulting services to vendors, and testing services to magazines. He pointed out that most sales claims and magazine tests were not meaningful in practice. His testing showed that most commercial designs were inferior to what he felt necessary. He designed a cyclone to meet the needs of a small shop, and offered the plans free to individuals to make one for their own use. Today only ClearVue manufactures a cyclone following Bill's design (and pays him a royalty for the design), but you can build one yourself for personal use without royalty (sounds like a professor to me). I don't know the details of the Oneida - Pentz battle. I don't know who was right or wrong. I am not sure I could judge the case on it's merits, so all I can do is report a battle between Bill Pentz, one of the world's leading experts on wood dust collection, and Oneida, one of the leading vendors in that field. | |
Over the years I have talked with numerous users of Bill Pentz's cyclone design, either home-made or bought from ClearVue, and they have universally been happy. I have talked with numerous Oneida customers over the past few years, many of whom have given good reviews as users of 2 and 3 hp Oneidas, as well as 5 hp (but don't expect the tiny Oneida systems with small hoses to compete with a "real" system). I have recently talked to a couple users with large shops and smaller Oneida cyclones who had less than great results - so don't get a unit that is too small for your shop, from Oneida or from anyone else. Although I still believe Oneida can be an excellent vendor if you get a big enough system, I chose a ClearVue for my own shop.
Effective dust and chip collection depends on a very large airflow. That requires large pipes (I had a huge improvement in my dust collection when I went from 4 inch to 6 inch ducts). You may be shocked to spend as much on ductwork as as on the cyclone.
That large airflow requires a large fan (impeller), driven by a powerful motor. The squirrel cage fans often recovered from old furnaces probably won't be adequate - I don't think they will maintain the necessary speed and volume to carry relatively heavy chips through pipes. Your dust collector motor may be the hardest working motor in the shop - 3-5 hp or more, running under full load (moving lots of air) for hours at a time, not just intermittent brief periods of heavy load while a tool is cutting. (Be careful... if you have a large impeller and motor, don't run it without the ducts and filters - the fan can try to move too much air and overload the motor.) And a 5 hp cyclone creates a lot of heat - not only from the motor and noise, but also from stirring a large volume of air through ducts, fans, and filters.
These are basically a low efficiency cyclone that is put "in line" prior to the primary (single stage or cyclone) dust collector. Any separator like this constricts the airflow, dropping the pressure, which reduces the air volume, so experts normally say they should NOT be used. However, I continue to use mine on my jointer/planer for a simple reason... it isolates the large volume of relatively clean chips, and lets the dust go on to the primary dust collector. (The inefficiency of a simple trash can separator helps here - the large chips are dropped, and the fine duet goes on to the main unit). As a result, people are often willing to take the chips for garden mulch or animal bedding. The really ugly dust at the dust collector has to be disposed of far less often.
When I had a single stage collector, I made a real effort not to open the plastic bag any more than necessary to get it out - it is really ugly fine (dangerous) dust. I probably got over 20 bags of chips for each bag of dust. Now that I have the more powerful cyclone, it pulls medium size chips to the cyclone, and only drops the largest at the separator, so I only get about 5 bags of chips for each bag at the dust collector. (I am experimenting with opening additional gates to reduce the suction at the separator, so more chips stay at the separator rather than going on to the cyclone). Also, with a single stage, there is positive pressure on the collection bag (it inflates). With the cyclone there is negative pressure on the collector (in suction) so I cannot collect directly into a bag without taking exceptional steps - I have to empty the collection can.
A fellow named J. Phil Thien tried the usual Rockler, Woodcraft, and Lee Valley trash can lids as separators, and didn't like the results - too many chips got through, and chips that had already been dropped were sometimes picked up and carried out of the separator (called scrubbing). He also has a small shop and uses a shop vacuum for dust collection. But his design of the Thien Separator appears very effective. (If you watch 5 minute version of his video, skip the first 2½ minutes.) In a few minutes I can make as much dust as he used in his demonstration of a "week's worth" of dust and chips, so I don't expect to go back to a shop vacuum driven dust collector. His design has been extended to versions that work with (or inside) conventional dust collectors. He also supports a forum to discuss his design - accessed from the link above.
More on chips: Walnut wood chips contain a chemical that prevents seeds from germinating and can reportedly kill horses when mixed with horse urine (don't use it for horse bedding). Not good for mulch? On the contrary. I have people asking for walnut chips for their flower beds. In my experience, a 1/2 inch layer (perhaps covered with other mulch, to keep it from blowing away) reduces seed germinating for several years. Since most weeds are spread by seeds, and it doesn't do anything to established plants, it is great for weed control It doesn't help with unwanted growth spread by runners or roots, but it sure cuts back on the weeds. Other chips (that don't include walnut) are taken by people who are making compost, reportedly ideally mixed with grass clippings.
You buy a high power cyclone, and connect it to your machines with large, efficient ducts. Is everything okay now? Sorry, but the answer is no. You are certainly far better than you were before installing a good cyclone dust collector with fine particle filters, but testing shows that too much of the fine dust still escapes uncollected - the fugitive dust. To be really safe, you should still wear a respirator, and continuously exchange the air in the shop with outside air. Living in the South now, and previously living in the North, I like heating and air conditioning - personally I am going to sacrifice some measure of health for comfort. Years ago I had a "wellness" doctor who carefully analyzed my diet, weight, activities, etc., and warned me that I could live longer if I stopped drinking, eating rich foods, and exercised more. How much longer? His analysis said 4 months longer. I made the decision to continue my wild life. I am starting from a very healthy level, but I have still made a major investment in collecting as much of my shop dust as I can at the source, through dedicated vacuums and a large, efficient cyclone.
A large professional shop may have truckloads of dust and chips - not me. Small shops typically have to bag their dust and chips, even if they go into a dumpster. If you separate the chips (see above) the total volume of dust is dramatically lower, but you still have to get rid of the ugly stuff. Many vendors suggest 6 mil plastic bags at a "bargain price" of $2 each. But I have found the 3 mil "Construction site cleanup bags" from Home Depot (and other stores) quite adequate at about 35 cents each.
Can you just blow the dust out of your shop and forget all the ductwork and filters? Yes and no. Where is it going outside? Next to your shop, where it will blow or be tracked back in? Into your neighbors yard? Probably not good options, unless you only do it with the air coming out of the cyclone, after most of the chips and dust have been removed.
The other very real problem with venting to the outside is the "make up" air. If your dust collector moves 1000 cfm, all the air in a typical one person shop will be removed in a few minutes. Replacement or "make up" air has to come from someplace, ultimately outdoors. It may need to be heated or cooled. And a good inlet needs to be provided - blowing some air out may suck the replacement air (and fumes) down the furnace or water heater chimney, or fumes accumulated in the garage. How do you spell poisonous carbon monoxide? One reader even suggested that the reduced air pressure in a basement shop, caused by exhausting the dust, would potentially increase the radon gas sucked in through the foundation. I am not an expert on radon, but I am much more worried about the bad air sucked in through the vents and windows than I am about a minute increase through the foundation.
Some people swear by the shop air filters, either from tool vendors or home-made from an old furnace fan and various furnace filters. They typically collect a fair amount of visible dust, and make the shop appear cleaner. However the relatively open filters in this type system don't collect the dangerous small dust particles. Some experts argue that they stir up the fine dust, and make health conditions worse.
If you have a good (cyclone) dust collector that moves 1000 or more cfm and removes fine dust, that means it filters an amount of air equal to all the air in your shop every few minutes. Rather than use a separate air filter, how about just running your efficient (cyclone) dust collector more, even after you turn off your major tools?
If you still feel the need for a separate air filter, Bill Pentz has a design for that also.
The ideal is to catch the dust as it is generated, at each tool, before it gets into the air. Some people have invested in a number of smaller dust collectors hooked directly to a machine, reducing the cost and losses in the ductwork. In some cases this may be the most effective solution, but in order to get the best out of it, you have to use a high quality filter, and you have to get great collection at the source. The problem with high quality filters on a single stage collector is that they tend to get damaged with wood chips larger than dust, and they need to be cleaned frequently so that the pressure drop across the filter doesn't get so big that the airflow drops, or the fine dust is forced through the filter medium, damaging it at a microscopic level.
I saw one shop that appeared much cleaner after converting from a distributed collector, at each machine, to a powerful central system. The cleanest one-person shop I have seen has a 5 hp Oneida cyclone, good ducting, and proper collection at each machine (even machines reputed to have poor dust collection). In both these cases, the central system seemed far better.
Some hand tools (especially those hand tools with a power cord, like sanders) have been designed "from the ground up" for efficient dust collection - especially the Festool line. I have a vacuum attached to my Festool (and other) sanders. I use a high volume shop vacuum on my sanders and other hand tools; it is a big help but isn't a complete solution. Further, my hand sanding still leaves my work and my clothes covered with fine dust. Some shops use a downdraft table... a table with holes or screen on the surface, with air sucked through the table (by a dust collector or a separate furnace-type fan) to capture the dust from hand sanding. Nice idea, but collection isn't very efficient, and it takes a lot of space.
What is the most dangerous tool in your shop? A saw that can cut off a finger? A lathe that can throw a large bowl at you? I believe it is the small air gun you hook to your air compressor. Blow the dust into the air - mix it up really well so that you can breathe it. That tool can kill you.
Since none of these approaches are completely satisfactory, some people use personal protective gear. The disposable masks for "nuisance dust" are not particularly effective. The respirators, such as 3M 7500 series dual cartridge filter respirator mask are far better, but not pleasant to use for hours at a time. The hoods that blow filtered air inside a face shield are expensive, but appear to be helpful.
Shop coats, aprons, hats, and other clothing that is left in the shop can be a big help in reducing contamination of the car or house.
If your home is connected to your shop (only a dedicated woodworker would say the home was connected to the shop, rather than the other order), then it is wise to keep a "negative pressure" in the shop. A small exhaust fan, like a bathroom fan, can remove enough air from the shop so that any air leaking between the home and shop, moves into the shop, rather than from the shop into the home.
What is the cheapest dust collection system? Not what I did!
Don't forget the hearing protection. I replaced my cheap Home Depot earmuffs with good ones from a gun shop. And one of my long-time friends reminds me that he has a collection of noise suppression ear muffs with broken plastic head bands - be sure the "good" earmuffs also have a good steel head band. He uses and recommends the Howard Leight Leightning L1 from Honeywell with a 25 db rating.
I also found a 3M Peltor H10A Optime 105 earmuff with a 30 db rating for only a little more cost.
And don't forget to contribute to Bill Pentz for his years of research in this field
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