click tracking

This webpage is about the various things I have done in order to control the amount of dust in my basement woodworking shop over nearly two decades now.

The first dust control device I bought was a good dust mask. I have used several different ones over time, and as long as you get the kind that have fine dust replaceable cartridges and form a tight seal on your face, I can't really say one is better than another. They all have worked, and they are all a bit of a pain, mostly because I also wear glasses and sometimes safety glasses over them. Add ear protection and yeah, it's a real mess. Nevertheless I use them, especially when using any sanding machine or a router, including my CNC router when cutting wood. If you are just now thinking of doing something about dust, start with a good mask and get used to using it, especially when sanding. Just get one that fits you well. Without question, your lungs are one of the most vulnerable and precious things in your shop.

If you think there hasn't been woodworkers who were forced to sell their shops due to lung problems, just talk to a pulmonologist, who is somebody who treats them for a living.

Besides the mask, the other simple thing you can do to avoid sawdust is to do as much dust-related work as you can outside. Even a small breeze does wonders to get rid of a cloud of dust around you, and cleanup is a snap. I kind of envy woodworkers who can roll out their router table or saws and cut on their driveway on a nice day, but alas, my shop has to be in my basement.

Even with the mask however, I began to become irritated (literally as well as figuratively) by the dust that formed layers on practically everything in the shop, and began to wonder about the inevitability of stirring up that dust just by moving around. Dust would settle onto drying coats of finish that caused more work and really bugged me. I knew I needed to do something.

One other thing that should be mentioned - like me, many others have their furnaces in the same basement area as the workshop. If so, pay attention to the amount of dust in the rest of your house. You might benefit greatly by doing some sealing work around your furnace.

If you have a gas furnace, the airpath that takes in room air, burns the natural gas, and is directed up the flue and outside, has nothing to do with your dust problem, other than keeping the furnace burner dust free is a very good idea. However, this is also exactly why you can't just blow the dust outdoors - you create a negative pressure in the basement that sucks the exhaust from your furnace back down into the basement, including the carbon monoxide which will kill you if you breathe enough of it - at least, don't do that while the furnace is running.

It is the air path that circulates the room air around the house that deserves attiention, whether you use gas or electric. Return airways have negative pressure and can pull dust from the basement air into its air stream so take a moment to trace out these ducts and use whatever sealing methods that are needed to keep that from happening. BTW, that is just what "duct" tape was designed to do! This exercise should also tell you what vents you have in the basement area, and you might want to close these off, or simply turn off the furnace and its fan while using dust generating equipment (but don't forget to turn it back on!) One area that can reduce circulating air pressure is where the furnace filter is inserted, but this is usually under higher pressure than room air, so the chance of dust getting in there is not as great. However, take a good look at those filters - if there is wood dust on them, you've got some leaks. Wood dust is usually a light yellow, while house dust is usually a darker gray.

Okay, all that is a good idea, but I wanted to get rid of the dust, not just confine it to my workshop. Thinking I should start small (which was, in retrospect, perhaps not one of my best decisions) one of the first things I looked at many years ago was a fixed room air filtration unit. These are sold commercially and are usually shown suspended from a ceiling. The ones I saw consisted of a box with a fan and some replaceable air filters to pull the room air through. Although I certainly agree that these units must be out in the open to allow the air currents their maximum reach, I don't think having them in a fixed location each time they are used is the best course - this would allow the inevitable "dead spots" of air flow to accumulate dust. I think being able to position the unit in various parts of the room, allowing the pattern of air currents to change, would be better in the long run.

Fig. 1

Figure 1 is what I made to address this - it is essentially a portable table with a box under the top that contains the blower. (In the picture, my shop built drum sander with its own dust collection port is setting on top of the air cleaner. There is almost always some tool sitting on top of the unit.) The blower is a 1350 CFM gable mount attic fan that I bought new for $72 (this was a while ago, so the price has probably gone up) with two high performance furnace filters, one on each side of the fan. I picked a common size for the filters, ensuring the widest availability of different types and grades of filters. I did need to provide a wire backing for the filters or they would collapse as soon as the unit was switched on. The filters also ride in aluminum tracks on the box, and the fit is tight enough that I haven't needed to apply tape or sealant - just do not try to remove them while the blower is on!

I don't have a dust measurement device to tell quantitatively how well this works, but I can say that it does what I needed it to do by this simple experiment - with it running, I can start applying polyurethane finish within an hour after using my sanders or routers, and the imbedded dust in the wet poly is less in my workshop than if it dries in another part of the house that is not exposed to workshop air, which is to say there is practically no dust in the finish.

Note: I didn't have a dust gauge when I originally wrote this, so I later built one using an Arduino and a cell phone screen, described here. That gauge tells me that this air cleaner does indeed reduce the amount of particulate dust in the air greater than 1 micron, (which is what it measures) but only after kicking up a lot of dust first. I have also since read that this approach does not actually do much to help the problem of finer dust, which is not measured by the gauge or trapped by the filters. So I don't look at it as a health related tool, but it does do what I built it to do - clear the air to be able to apply a nice dust-free finish on the wood. Now, I always turn it on after I am done sanding and I leave the room, and I am also absent from the shop for a while after turning it off.

Fig. 2

Later I bought a Shop Vac that uses a 2 1/2 inch hose for pulling out some of the dust, but pretty quickly tired of buying filters for it. To mitigate this I took the easy way out (I usually like to make things like that) and bought an Oneida Dust Deputy kit - the white cone shaped thing on top of the bucket above since it was so well recommended. To make use of it in practice you really need some kind of support or cart for it all and I built the one in the photo based on a design in Shop Notes issue 109. I must admit this thing works very well, and I often empty the white 5 gallon bucket but rarely have to vacuum the filter inside the shop vac, except after MDF work, but even then it is very light. After 4 years of use, I have never emptied the Shop Vac, and it is still empty!

I know that there must be some amount of suction energy consumed by a separator to form the cyclone. However, When I feel the suction of the Shop Vac before attaching the separator and watch it pick up dust, and then do the same again after attaching it, the difference is just not noticeable. I realize this is a long way from a scientific measurement of vacuum pressure, but I think I would have noticed any significant drop so I am going to place this set up in the spreadsheet column labeled "pretty darn efficient."

Nothing is perfect, though. The downside to this system is that most shop vacs (mine is an actual Shop Vac brand) are not designed for continuous duty, even the ones marked "industrial" or "heavy duty". Normally, this is not a problem since we usually don't operate power tools continously but my CNC machine sometimes requires long operations. The one in Figure 2 needed the motor/impellor unit replaced (about $50) because I ran it during a CNC run that lasted for many hours, and this was after it already saw several years of use. The Shop Vac tech I spoke to when I ordered the replacement motor said these units will burn out with that kind of long period of operation. If the motor on this one dies again, I will probably not replace it, but look for a different unit.

Fig. 3

Over 15 years ago I bought the Dust Collection system shown above. A review in a magazine I saw way back then gave it high marks, but this was before the work of Phil Thien and Bill Pentz was well known. This is the Penn Industries DC-1BXL that sports a 1hp motor and 10 inch impeller which only draws 850 CFM. It originally came with a 5 micron bag (I believe they now ship with a one micron bag, but within a couple of years I upgraded to the canister filter shown above that has an even finer rating. My experience with this unit is mixed - it has been very reliable, and it is exceptionally quiet compared to other guys' DCs I've heard. The problem is that it simply doesn't have enough power to grow, and I probably never should have bought so small a unit in the first place, but it was "hot stuff" back then. Now, a more powerful unit can be had from Harbor Freight for half the price!

Fig. 4

Right after I changed the bag on the DC for the first time, I started looking for a separator. Remember, this was back in the days when the idea of a separator was still new to most woodworkers. I bought one of those plastic garbage can separator lids shown above and lived with it for a while. The holes for the hose are not designed to be used with conventional hose - you have to come up with some way to seal them yourself. While it captured the bigger chips, it passed a lot of dust and chips on to the DC. It seemed that for every 3 times I emptied the garbage can I needed to empty the bottom bag on the DC. This was after taking further steps to ensure a good seal around the hoses and the garbage can rim, and there was a noticeable drop in suction. Still, it was able to pull all the chips and dust from my table saw, but this was no where near the kind of separation the Dust Deputy was giving me. I cannot recommend this patented lid separator - it is a good example only of how something doesn't have to actually work well to get a patent on it. [Later note: here is a guy who had this separator, and used it along with a (kind of) Thien baffle to make something that worked for him, but we seemed to have the exact opposite experience with it.] I began looking around for something better.

I looked at building a cyclone, like the one in Wood Magazine (the November 1997 issue - I think I missed it when it came out, but it came to my attention later) or the one Bill Pentz provides information for, but that was going to cost some real money since they both required a larger impeller and a bigger motor. I was seriously thinking about trying a Super Dust Deputy from Oneida because of my good luck with the smaller one, but the kit (just cyclone body alone) was $180 and there was still the possibility that my DC might not work with it.

I asked Penn State Industries on their forum what kind of separator they would recommend for the DC-1BXL, and their representative answered with this: "Separators are usually recommended for more hp, and more static pressure to play with, the pre separators take a great deal of your consumable CFM, and static pressure, I [sic] my opinion you will waste a lot a valuable air where you need it"

Okay, so Penn Industries didn't think their $300 "award winning" DC-1BXL had enough power to work with any separator. However, this just didn't seem to jive with my experience of the lid separator, which despite its air loss and lousy efficiency, was still able to pull the air and its dust from my table saw, and the efficient Dust Deputy whose loss didn't seem to dent the static pressure of its air stream at all. I know the two devices (the DC and the ShopVac) work differently, and are meant to be used in different ways, but I suspect that some of the numbers that are commonly used to estimate their performance are a bit conservative.

I came across J. Phil Thien's work. A Thien separator, sometimes called a Thien baffle, is a device to direct an airsteam with dust in it to allow the dust to fall out of the airstream. It can be used between the DC blower and the tools that generate the chips and dust, just like the Dust Deputy, or it can be placed after the blower inside a DC. However, in the former configuration it also keeps debris from reaching the DC's impeller, thereby protecting it. Phil Thien has a website about his work shown here.

I realized for very little time and money I could try one out and see if it would be any better than what I had. After a very brief introduction to what the baffle idea was on his website, I began wading through the many, many forum comments and realized the one shown on Phil's website probably wasn't the one I wanted to build. The configuration I decided to build is called a Top Hat separator, also described in Thien's forum area, and was originated by Bruce Wrenn. In this design, the separation chamber and baffle simply rests on top of the bin (a metal garbage can in my case) rather than being placed down inside it. The top hat approach allows a better seal of the baffle to the sides (the top hat sides can be caulked, but the lowered baffle cannot) and it also eliminates having a large 90 degree elbow right in the middle of the separation chamber airflow.

After looking at top hat separator designs built by others, I decided on a layout similar to one built by Jason ??? (aka Pitbull aka Rawdawgs50) who says he got it from someone named Vawoodworker84. It's perfectly true that we are smarter collectively than we are individually. So, I started laying out the design on some material.

Fig. 5

Figure 5 shows the bottom of the separator that will rest on top of the garbage can. It is made out of MDF, and is yet-another-reminder of why I really don't like working with MDF! Unseen on the underside of this is a circular pocket cut into the bottom that snugly fits the rim of the garbage can. That pocket can be seen below in Figure 10.

The item in the middle is a beam compass that I used to lay out the circles. I made this one, but I am pretty sure some guy in ancient Egypt or Sumeria should get the credit for being the first to think one up, although the wing nuts and bolts are a bit more modern. Behind that is a router circle jig (trammel) I made from some 1/4 inch Lexan. I dedicated an old $20 HF trim router to it and the whole thing including the router cost less than an off-the-shelf circle jig alone.

The "C" shaped cutout shown above, which goes 240 degrees around, is the heart of the Thien baffle.

My understanding of the way this thing works is this: When your DC is turned on, the impeller creates a vacuum through the duct into the middle of the separator chamber. Air from your tool rushes into the separator inlet at a tangent, causing a shallow cyclone action along the sides of the curved walls. Eventually the air evacuates up into the center outlet. When your tool creates dust into this airstream, it enters the chamber where gravity begins to pull the dust down into the slot while centrifugal force keeps the dust, which is heavier than the air, along the side walls. The dust collides with the side walls, slowing it down, and it falls into the slot. The chips and dust may make several trips around the separator before they fall. Anything that doesn't make this drop goes up the outlet and into your DC filter or bag. Perfect separation is defined to be when nothing makes it into the bag and everything, no matter how small the dust particles are, goes into the bin. Unfortunately, nothing is perfect.

The bulk of the area in the middle of the "C" is there to keep the dust from blowing back up from the bin into the air stream. The part at the rear of the photo sticking out tangentially is the bottom of the air inlet. My "C" drop slot is 1 1/8 inch wide. The thinner the slot, the better job it does keeping the finer dust in the bin. If the slot is too narrow, the larger chips may clog, so a 1 1/8 "rule of thumb" about this width has evolved.

Fig. 6

These are the upright pieces used to attach the top to the bottom and give the side walls something to rest against. They will be glued and screwed into, so I used hardwood for them. There is a small vertical notch on the left end of the rearmost upright to give the end of the sidewall something to fit into, and the left end of the smaller board is cut at an angle to match the groove where it meets the side wall.

Fig. 7

In Figure 7 is the top of the separator, turned upside down so you can see the slot I routed into it to hold the side walls in place. This outer slot diameter matches the outer diameter of the "C" slot in the bottom. There will be a 4 1/8 inch hole cut in this top for the outlet. In the picture, the top is just sitting on the same bottom of the separator that is shown in Figure 5 and 6.

Fig. 8

Here the unit is starting to come together. The top has its outlet cut and the port (a 4" hose splicer) is press fit into place. Another rule of thumb that has developed is that the lower edge of the port should be 1/2 of its diameter above the bottom of the separator, or 2 inches from the "C" middle surface. I've also beveled the inside edge of the "C" from the bottom to make the edge esposed to the air thinner and thereby make it easier to get the dust below. I also applied a roundover bit to all the external exposed edges.

Fig. 9
Fig. 10

I began to have second thoughts about sealing this thing up since I won't be able to get back inside the separator once it is assembled. Is there anything I will later wish I had done before this point? Hmmm. I drilled a couple of holes in the top and affixed some 1/4-20 flat head bolts, sealing them in with construction adhesive. These will be hard attach points to facilitate fastening something later, like a hose support or a lifting handle.

Does anyone not have a collection of those free LED flashlights that HF gives away for a coupon? It turns out these flashlights fit really well in a 1 inch hole, which I drilled at the front of the separator so that it would shine into the chamber, as well as down through the drop slot into the bin, shown in Figure 10.

I thought about just sealing this flashlight in place, but sanity prevailed and instead I inlaid a square scrap of Lexan on the bottom using a router and epoxy. This is shown in the inset photo of Figure 9, showing how it is inlaid to be flush with the underside of the top. Now I can remove or replace the flashlight at will, and I can not only see the swirl of the dust in there while it is running, but this should provide enough light through the drop slot into the bin for a dust level indicator down there as well. Out of pocket cost? Zero.

Fig. 11

All of the wood and MDF parts shown in Figure 8 got many coats of poly - there is 3/4 of a quart soaked into them! I thought in this case it made sense to paint the top and bottom before I caulked the walls in place. Although I rarely paint wood, the inside of the chamber was left with the poly surface, and the outside was painted to match the DC. In the above photo, you can see the unit upside down, showing the outer ring I routed for the garbage can rim, as well as the bevel I routed on the inner edge of the "C." The garbage can rim pocket is 18 1/4 inch in diameter to fit my 30 gallon metal trash can, and will have some weather stripping foam placed in it to help make the seal. Also, the hole in the center for the trammel had a dowel glued into it and flush cut.

Fig. 12

Here, the Lexan is given a trial fit. I had some 1/8 Lexan on hand I wanted to use, but I didn't have a piece long enough to go all the way around the "C." I cut two pieces that meet in the center of the support where the arrow marked B points. I used a strip of shipping tape on the outside of the two pieces, hidden behind the support, to keep them together. At the point marked by arrow A, there is a 1/8 inch rabbet cut along the edge of the vertical board to give the Lexan something to fit into. The top edge of the Lexan is sitting 1/4 inch proud of the uprights to fit into the "C" slot shown in Figure 7. After assembly, each square open area of the Lexan will be sealed.

Fig. 13

Some of the forum members on Thien's website have shown the efficacy of using a bellmouth shape for the separator outlet. I got the one shown above, a 4 inch one from Parts Express for $4.44, part number 268-376 and is normally sold as a port tube mouth for those building their own audio speakers. Although it is a 4 inch ID flared tube, it actually wants a 4.125 inch hole to fit into. I figured for those few bucks it was worth a try.

Another rule of thumb that has been experimentally determined is that the outlet should extend down into the separation chamber such that the gap between the surface of the bottom and the outlet rim should be half the diameter of the outlet, or in my case 2 inches.

Fig. 14

Above, the completed unit has a 4 inch port attached to the inlet, and all is glued, screwed, and sealed into place and ready to test. I used a clear sealer called Polyseamseal which is a bit stronger than silicone.

Fig. 15

Above is the completed top hat on the garbage can. The 30 gal garbage can has a hole cut in the side and a piece of scrap Lexan bolted and sealed in place, right under the light so that it is illuminated from above. The can itself fits over a round piece of MDF with 4 casters under it to make it easy to roll in and out from under the separator. I will probably make some kind of locking arm to lift the separator up while rolling out the can to empty it.

Fig. 16

Here is the system in the corner - the DC is elevated on a table made from scraps to make the hose connection to the top hat easier. Despite the low power of the DC, it seems to pull almost all of the dust of the table saw into the unit. Although I do not have a top dust collection fixture over the blade of my saw, there seems to be little dust that comes from that. I think this is largely due to using zero clearance inserts in the saw.

On Thien's forum, an air straightener is used to eliminate air circulation from the separator having to fight with impellor circulation in the opposite direction. In this case, the spin of both is in the same direction, so little would be accomplished with that. Also, making the chamber taller is recommended for "better separation of fines" but without any way to quantify how much better that change makes (the observed change is subjective) I'll just see how this one works.

Note: Later, I did something about that. On this page is a description of building a Shop Dust Gauge to measure the amount of the dust in the air.

About 6 months later:

I've used this now through many projects, and it works really well - the bin fills up and there is just a light dust in the DC bag, and I regularly knock the dust down on the top filter. The first time I tried it, I was impatient and used it before I applied the weatherproofing seal between the bin and the separator, and I was disappointed in the separation I was seeing. After applying the seal and doing a little filing on the rim of the garbage can, it worked great, so getting a good seal between the can and the separator is very important. If you make one and it isn't working well, first thing is to check for leaks. It might have been easier if I had used one of those Brute plastic garbage cans as they have a very smooth and uniform rim, but I am happy with what I have and see no need to replace it.

I also spent some time making better seals around my table saw box which made a big difference at capturing more of the airborne dust. On my saw, the motor mount on the back makes it particularly difficult to get a good seal, and I still have to remove some of the seals for an angled cut, but that is somewhat rare.

Over on the Thien forum, an intrepid researcher there named retired2 did some great tests on both the bellmouth enhancement, as well as the idea of using an air straightener mentioned above. The data looked convincing, regardless of the rotation of the air, so I decided to try it. I added about a four inch long straightener in the hose section between the DC and the separator using a combination of florescent tube protector lengths and a few soda straws around the outer diameter to make a tight fit. I couldn't hear or measure (I used a sound meter) any difference before and after in the sound level, or notice much difference in either suction (just observation - not a good measurement, to be sure) or current draw using my Kill a Watt meter, but like the bell mouth, it was cheap and easy to try. I take his word for it that it helps some.

Here is a video of some material being cut and the resulting dust in the separator chamber. Sorry about the grainy look, but I needed to do this in low light conditions to make the dust stand out.

The first two cuts on the table saw was using some oak, followed by two cuts of MDF which you can see looks cloudy and denser. It doesn't take long at all for the dust to clear after the cutting stops. In three dimensions you can see how the dust is contained in a doughnut shape around the outside rim,while it drops into the slot, and the center remains clear. Other than a small amount of very fine yellow powder that makes it through when cutting MDF, practically nothing makes it into the DC bag.

Another way to achieve better efficiency would be to add another baffle in the DC right above the bottom bag with a narrrow gap. Since the only thing making it this far are fines, the gap on this baffle can be small, and might reduce the dust that settles into the canister filter. However, my filter has a paddle that is rotated periodically to shake off accumulated dust, and the baffle would prevent that dust from falling into the bag. There's always trade-offs.

Anyway, this unit wouldn't be up to powering a whole shop vacuum distribution system, since all those pipes and fittings would reduce the air movement too much, but for a "one machine at a time" kind of system, this will do, and it didn't break the bank!

Thanks for looking!

Comments may be addressed to gary at liming daught org.