If you have a shop vacuum you know how the suction drops off as the filter gets clogged with dust. You also know that cleaning the filter is a very unpleasant job. This situation has lead many many people to come up with some kind of a pre-separator solution for their shopvac.
On the commercial side you have things like the Oneida Dust Deputy, or the Clearvue mini. On the home built side you have home built cyclones based on the well-known Bill Pentz guidelines or other variations on that. Another well-known home-built solution is the Thien Baffle. Just ask Google and you will find many web pages out there with people trying to solve this problem.
My own project here began with copying Ryan Nodwell of shopbuilt.org's Super Easy Cyclone Separator. I added a Thein Baffle onto that to come up with my design. I have also seen many other similar projects online, and I've drawn parts from many of those sources as well.
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Step 1: Start With Two Buckets, and Some Scrap Plywood
I'm starting with two buckets. Both were freebies rescued from the trash at some point. Both, coincidentally, were originally used for bulk laundry detergent storage. Neither has a lid. The large bucket will go on the bottom to receive the dust and waste. The small bucket will be flipped upside down on top, and that will be the Thien Baffle separator.
I also have here some salvaged scrap plywood. This used to be a classroom desk top so it is thick plywood coated with a 1/8" thick plastic top coating. I have traced out the circumference of the top bucket, and then measured and marked for the cutout.
FInally, here is the completed plywood disk with cutout. This will mount on the bottom of the top bucket. Dust will enter the top bucket and spin around the outside, lose velocity and drop through the cutout, while the air will continue on out through the top of the "cyclone" and on to the shopvac.
I'm glossing over design details here. This disk is the basic heart of the Thien Baffle design, referenced above.
Step 2: Add a Ring to the Baffle
I have no lids for these buckets, so the baffle disk needs to also serve as the lid for the larger bucket. Here I traced out the buck and cut a 1" wide ring from more of that scrap plywood.
(If you build this, I would suggest making the ring 1-1/2" wide, as that would make it a bit easier to attach to the baffle disk. Make this and the disk 1" wider in diameter and it should work.)
The two piece are glued together and they fit snugly over the large bottom bucket. The bottom bucket is simply held in place with friction, and then with air suction while the system is running.
The small upper bucket will fit upside down on top, as shown in the last photo.
Step 3: Finishing the Top Bucket Separator
I made some wooden L-shaped buttons to act as clamps to hold down the upper bucket. I'm not ready to permanently affix it with glue and caulking. I'm not sure if I ever will, as it is nice to be able to open it up.
I have two shop vacs; a large old one, and a small salvaged unit. So I have a few extra implements that I can now use for this project. On the left (held by the bottom half of my hand) is a crevice tool. This will be cut down to be the inlet to the cyclone. On the right, and not easy to see as it is not in profile, is a surplus floor sweep. I will cut the bottom off of the floor sweep, leaving just the collar. I will attach that through the top/center of the cyclone. By using these old shopvac parts, I can guarantee that my cyclone will be easy to attach to shopvac hoses.
I marked a small door-shaped outline on the side of the upper bucket and cut it out with an oscillating tool. (visible on the bench beside my hand.)
Step 4: Thien Baffle Details
Here is the upper bucket fully assembled. The cut-off crevice tool is glued into the door flap, to act as the "injector". The cut-off floor sweep is glued into the top/center of the upper bucket.
What I don't show or explain well in the video is positioning of the inlet. (This is covered on the Thien Baffle website.)
The inlet is positioned at the end of the opening that was cut in the baffle disk. This is difficult to explain, so here are two sketches that explain it much better with a top view and an angled view looking down into the top bucket (top is removed in the sketch)
Step 5: Final Thoughts
And this is how it all goes together. The upper bucket is fitted onto the lower bucket, with the baffle disk in-between. The shopvac is connected to the top (outlet) of the cyclone. Another hose is connected to the inlet/injector of the cyclone and you use that for vacuuming.
For testing purposes I first grabbed the hose from my other shop vac. A week or so later I went out and bought a replacement shopvac hose kit. For the hose kit, I bought a 1-1/4" diameter hose. During my testing I found that the cyclone worked, and I could suck up the dust off the floor. However, the suction felt like it was a lot less than just sucking straight from the shopvac. Bear in mind that this is an empty shopvac with a moderately clean filter. I did not conduct any scientific tests. I really don't have the background for that to do it properly and fairly. I just found that this works well enough and it should work fine for my needs. I will primarily use this in the corner hooked to my X-carve CNC, or for light use in and around my bench, such as with my pocket-hole kit, or hooked up to a sander. Since the suction seemed lower, I bought a skinnier shopvac hose to use on the inlet. I was hoping that by cutting down on the diameter I would get a faster air stream. It seems to help. Time will tell.
And the obligatory closing shot showing the cyclone sucking up dust off of the floor. This part looks much better in the video.