How I Squeezed 2HP DC Under a Workbench

[Ed Garrett]

My shop is tiny but I have big dust control ambitions. My wife vetoed my “cyclone outhouse” concept, so I got drastic and combined an HF DC, ductwork, a downdraft table, and a TS outfeed table all into a single unit. If you’ve got similar space limitations you may find this useful.

My basic idea was to build the DC system into the structure of the table. I ditched everything but the blower and cyclone component, modified the intake to 6”, and ran two 4” PVC lines to each tool (6” ductwork would not have fit).

I opted for no filter. Just spin it and spit the fine dust outside. To save vertical space, I flattened the exhaust duct by turning the exhaust airflow downward with a stainless steel salad bowl (cut in half) and a modified 8” T. The 8” exhaust pipe exits through the floor and blows out across the grass. Apparently most of the fine dust just floats away in the breeze.

The downdraft table is unconventional too. The suction holes are 2.5 inches in diameter, allowing for huge airflow around small to midsized items being sanded. The holes also accept clamps. I just have to take care to keep unintended small objects away when the DC is on.

If I ever get a big shop, I plan to get a big cyclone (and a big everything else too), but for now, this setup is working well and only ran about $400 including hose, ducts, gates, etc. However, it did take a lot of work...

[Jaze Derr]

wow, that is a lot of work!

I'd probably lose a shop cat in that downdraft table, though...

[Mark Elmer]

I'd probably lose a shop cat in that downdraft table, though...[/QUOTE]

"Whirrrrr" "Meooooooooow" Whoosh "Kitty? Here kitty, kitty, kitty"

Not good. I don't allow my cats in the shop. A few good hand claps gets them moving.

[David Hostetler]

Okay I will admit to being dumb here. How does that thing function for filtration or separation? Just WHERE does the dust, chips, and shavings go?

[Doug Carpenter]

Maybe gettig rid of shop cats is the whole point.

I think your neighbors are going to wonder why their house is so dusty this summer. LOL

[glenn bradley]

Ed that rocks. You really took the bull by the horns given the space and SWMBO limitations. Well done.

P.s. At risk of offending any cat-lovers, feel free to feed that thing all the cats that like to hang out in my side yard. Man they are slow learners.

[Bill Blackburn]

Great space packing ingenuity there! Helluva lot of work - I don't have it in me. You for rent there Ed?
At the risk of offending dog lovers I'd welcome ya to feed all that crap all over my property into it too. Last few years I have developed a very strong distaste for them, and this is coming ffrom a 35 year, in a past life, dog breeder. Irish Setters and Chocolate Labs mainly. Love them but don't want 'em around anymore either. Crap and Yap is what I say....lol

I can handle the cats myself ... don't bother me much with the piddly size of the crap they leave behind. Figure 20 cats = one dog

[Ed Garrett]

I have no cats to test this system, but it does filter dust and chips pretty well. There is no direct filter, just centrifugal separation followed by depositing the dust and chips in an airflow dampened chamber.

Attached is a photo of the chips actually being collected. The perforated black component is an inverted plastic barrel I drilled 2.5-inch holes in to collect dust and then protect the collected dust from being scrubbed out by spiraling airflows during subsequent uses. In the picture you can actually see a streamer of dust terminating into one of the holes.

In honor of the TSA, I call this a "Full Body Baffle". As the dust laden air circles the baffle, the dust ultimately falls into the holes and collects within the barrel where it remains unmolested by turbulent air. When full, I take it outside, pull the barrel upward, and throw out the bag of dust.

So far it works great. There is remarkably little dusty residue to be found on the grass just beyond the 8" exhaust pipe. I assume there is plenty of suspended dust carried away on the breeze, but it must be so fine that can't even see it. Apparently it disburses into the atmosphere and contributes to global warming.

[Michael Weber]

So the inverted barrel is INSIDE a regular plastic collection bag? Kind of confusing for me but can see how that would work. First time I have seen this idea. Original?

[Ed Garrett]

Yes, the barrel is inside the bag. Original? I don't know. You could say it's effectively a Thein baffle on a perforated pedestal. The idea was to slow down the dust laden air and then give the dust a place to hide from the energetic air above. Bottom line: It works.

[David Hostetler]

How are you verifying that it works? It is entirely possible that you are blowing the ultra fines back in to the air by not filtering it, and you may have just created a 2HP dust pump...

Are you testing with a particle counter of some sort?

[Mike Cutler]

I like it Ed. I like it a lot in fact!
I see a makeover for my Jet DC 1100 in the near future.

One question;
How does the perforated barrel insert separate from the plastic bag when you need to empty it?
it looks like you just have to pick the whole thing up, and then remove the barrel insert. Yes, no?

[Ed Garrett]

Great questions. Here are my best quick responses:

David:

It works only because I vent the exhaust outside. I wouldn’t think of pumping it back into the shop and breathing it. I’m sure there are lots of ultra fine particles remaining in the exhaust. Success in this case is avoiding pumping sufficiently large dust particles that they would tend to collect on the lawn and invite another veto from my wife.

I initially started with a conventional Thein baffle (in addition to a circular bulkhead inside the cyclone unit), but was disappointed to see through the clear bag that the collected dust was still getting spun and scoured of fines. I remember reading a Bill Pentz passage that basically described the ultimate dust collector as an [infinitely] large drop box that would allow the energy/turbulence to drop to near zero, which would allow nearly all the particulates to settle out. My idea with the three dimensional baffle was to create an interface that would exploit the difference between the turbulent energy of the spinning air outside the barrel and the more tranquil air on the inside. The turbulence of the air spinning outside the barrel tends to kick the particles through the holes where they are more prone to settling in the relatively calm environment. I theorized that only a tiny percentage of particles that made it into the barrel would come back out because there’s less energy in there to kick them out. Thus the holes in the barrel effectively behave as one way valves. I thought of it as a black hole for sawdust. Once the dust passes through the interface, it can’t escape.

I’ve made no measurements to prove any of this (I don’t have the gear), but I have observed that the collected dust contains a lot of very fine particles (like baby powder). I still feel sure that some, perhaps most, of the very finest particles do escape by simply riding the high speed air down and around the barrel a few times and then up and out the exhaust system. From what I’ve read, the finest and most harmful particles to the lungs are the sub-micron sized particles that can also squeak through filters. I’ve read all the arguments about filtering. Without pretending to actually know myself how well filters work on fines, I decided to play it safe and felt best about just venting it outside. I presume that once it’s ejected from my shop, it quickly gets diluted to harmless concentrations as it floats away. It must really be fine because I sure can’t find any deposited on the grass.

I did try some experiments when I initially observed that the collected dust was still getting spun and scoured in the unbaffled air. I tried placing various objects in the bottom of the bag thinking they would absorb the energy in the air, slow it down and leave the dust unmolested. I tried a concrete block, various combinations of bricks and plywood, and finally a stool. I even tried constricting the middle of the bag with a bungee cord serving as a “girdle” to emulate the cone of a cyclone. None of these things appeared to solve the problem. If anything, they created more turbulence. The air looked even more aggressive at relaunching particles. I came to the conclusion that instead of calming the air, I was breaking the circular laminar air movement into more random turbulence. I was doing more harm than good! That’s when remembered Bill Pentz’s drop box notion and I began to think of methods to isolate a volume of calm air from the violent spinning air that enters the bag. I’m familiar with the concept of osmosis and tried to think of macro-size analogy. I came up with various themes for making a “membrane” out of materials like fishnet fabric, hardware cloth, and pegboard, but before I burned up a bunch of effort making a permeable device, I saw the plastic barrel and decided, “why not drill some holes in that and just see if it works…” The beauty of the barrel solution is that it’s round and the radius is about 1 inch less than the clear bag. The revolving air flows pretty smoothly as you can see from the photo with the streamer of dust. Anything I would have made out of pegboard would have had corners, and again would have introduced additional turbulence within the bag. I just guessed what size holes to drill. Maybe I should have used more numerous smaller holes, but I was apprehensive of “ribbons” of wood clogging the holes.


Mike,

I discarded the lid of the barrel and turned it upside down. The top (formerly the bottom) of the barrel now just has one small hole in the center that I stick a finger into in order to lift it off the sawdust. The barrel just pulls straight up and leaves the sawdust behind in the bag. When I change bags, I detach the bag from the cyclone, slide it out from under the workbench with the barrel and sawdust still inside, carefully walk it outside, and then extract the barrel from the sawdust and the bag. That’s when I do actually get some sawdust on the grass. Good luck.


Sincerely,
Ed Garrett.