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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 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.
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, also certainly fine dust that I couldn't see.
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 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. It was a big improvement, but not the 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 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 a 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. 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). At a critical point, most of the dust has dropped and the air is sucked out, through the fan (note that most of the debris is gone before it goes through the fan). After the fan, the air passes through a filter, typically a large, very fine filter (the second stage). However, with little dust left in the airflow, there is little contamination of the filters - very little dust remains at that point, so the filters remain very efficient.
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 slow the air the most, thus requiring the largest motor and impeller (fan) to operate.
Bill Pentz designed a cyclone for optimum performance and published the plans to allow woodworkers to freely (no royalty) build one for their personal 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 in excellent. Clearvue Cyclones is the only vendor currently licensed to use Bill's design in a commercially available cyclone. Clearvue also has excellent tutorials on their site.
Effective dust and chip collection depends on a very large airflow. That requires large pipes (a huge improvement in my shop when I went from 4 inch to 6 inch ducts). That requires a large fan (impeller), driven by a powerful motor. 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 while a tool is cutting. (Be careful... if you have a large impeller and motor, and take off the load of the ducts and filters, the fan can try to move too much air and overload the motor.) You may be shocked to spend as much on ductwork as as on the cyclone.
These are basically a low efficiency cyclone that is put "in line" prior to the primary (single stage) dust collector. Any separator like this reduces the air flow, so can be considered a negative. However, I continue to use mine on my jointer/planer/shaper for a simple reason... it isolates the large volume of relatively clean chips, and lets the dust go on to the primary dust collector. As a result, people are often willing to take the chips for garden mulch (I can even sort by wood species, as different projects go through the shop). The really ugly dust that remains has to be disposed of, from my dust collector, far less often (probably over 20 bags of chips for each bag of dust). I make a real effort not to open the heavy plastic bag from the dust collector any more than necessary to get it out - it is really ugly fine (dangerous) dust.
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 - the dust collector may suck the air (and fumes) down the furnace or water heater chimney. How do you spell carbon monoxide?
Some people swear by the shop air filters, either from tool vendors or home-made from an old furnace fan and disposable 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.
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 is that they tend to get damaged with wood cuttings 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 had a 5 hp 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 tools 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. However, my hand sanding leaves my work and my clothes covered with fine dust, so this isn't a complete solution.
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 like to argue that it is the small air gun you hook to your 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, many people use personal protective gear. The disposable masks for "nuisance dust" are not particularly effective. The respirators with cartridge filters are far better, but not pleasant to use for hours at a time. The hoods that blow filtered air inside a face shield may be a good solution for some.
Shop coats, aprons, or 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 list them in that 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.
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