Monday, November 21, 2011

My Thien Dust Collector

I wanted to upgrade my dust collection system.  I have a Jet DC-650 dust collector that I bought in 2003, with a good pleated filter on top, and a plastic bag on the bottom.  The filter is stock, and according to the particle counter I borrowed, it does a very good job of catching all the finest sub-micron dust.  However, I really hate emptying the bag, because it attaches with this sleek-looking but fiddly internal spring ring.  It takes a lot of bandsaw or table saw use to fill it up, but the planer especially will generate large amounts of big shavings.  I'd also like to have something between the blower and the intake because what happens if I accidentally suck up a larger chunk of wood or a nail?  Whang!  Into the impeller, and then it gets flung into the bag where it pokes a hole.

There are trash can lid separators, but they don't work well.  I made one of my own several years ago and ditched it pretty quick.  A cyclone separator would be good, but they're expensive and take up a lot of room.  Fortunately, a guy named J. Phil Thien came up with a pretty slick and simple dust separator that combines the functionality of a cyclone with the compact form of a trash can lid separator, and he put the idea up on the web for people to build for themselves.  What a guy!  I printed out a couple of pages from his website, and they've been sitting in my pile of shop papers for a few years.  Last week, I finally got around to building one.  I made it in a "top hat" style so that the separation happens in a separate unit above the trash can, and all of the volume in the can is available for debris.

I bought a quality 10 gallon metal trash can first, about 18" tall x 14" diameter at the top.  I had a couple of 16" x 15" pieces of 3/4" melamine particleboard left over from a shelving project, so those became the top and bottom plates, and I got a piece of 1/16" clear polycarbonate 8" x 48" custom cut from TAP plastics for $10.  Polycarbonate is flexible, and will stand up to impact a lot better than acrylic, so I chose it for the walls of the separator.  It's also nice to be able to watch the thing in action.  You could also use sheet metal, which would definitely be more abrasion resistant, but I don't think it will be a problem.  The inlet is a 4" plastic dust collection elbow, and the outlet is a 4" angled coupler.

I used a circle jig and router to do almost all of the shaping.  First I used a 1/2" bit to cut a dado in the bottom plate the same 14" diameter as the trash can, about 3/8" deep.  This fits over the rim of the can and holds the separator in place.  Then I used a 1/4" bit to cut slightly smaller diameter dadoes in both the top and bottom plates, about 1/4" deep.  This will hold the polycarbonate sheet I used for the sides.  Then I used the same 1/4" bit to plunge all the way through and cut the drop slot.  This slot is 1-1/4" wide, and goes 2/3 of the way around the circle of the lid.  I set the circumference so that the outer edge of the slot is about 1/16" inside the 1/4" groove for the sides so that the inside of the walls is flush with the outer edge of the slot.  I hope all that makes sense because I didn't stop to take photos.

Here is the groove to fit the trash can rim.  I've marked the ends of the drop slot.
I couldn't find my angle gauge, so I resorted to some late night trigonometry to figure out 120˚.
Too bad I didn't remember this trick.
Then I used a 4" hole saw to put a hole in the center of the top for the outlet, and another 4" hole in outer portion for the inlet.  I used three pieces of #10-24 threaded rod with nuts and washers to clamp the polycarbonate sheet in the grooves between the top and bottom plates, after putting a bead of caulk into the bottom groove.  I fastened the overlapping ends of the sheet by drilling holes and putting some #4x1/2" pan head screws through and into a strip of plywood.  I added a strip of self-adhesive rubber weatherstripping to the dado that mates the top to the trash can, because any little leak into the space below the drop slot plate is a big problem for this type of separator.

I hooked it up and the first thing I tried was cleaning out under my table saw.  I have a panel installed in the bottom of my contractor's type saw as part of the dust collection setup.  It accumulates a lot of dust and chips, and I stuck the hose in there and vacuumed it all up.  Just like a cyclone separator, it swirled against the clear sides in a downward spiral, and then dropped into the slot.  Pretty cool.  Only a layer of fine dust accumulated in the dust collector bag.  Here's a video.

Update:  I've been using it now for a couple of weeks, and it does just what I want it to do.  I've filled the trash can a couple of times and very little has made it to the dust collector bag.  I built this pretty fast, just to test the concept, and there are a couple of things I don't like.  The configuration requires a lot of elbows, which adds bulk, makes the hose fall off sometimes, and the inlet elbow inside causes a lot of turbulence.  I'm sure a side-inlet version would work a lot better, but I've got actual projects to deal with for now.