My shop vac filter element was plugging up with dust much to frequently for my tastes. To reduce the dust loading to the filter, I built a cyclone separator to act a a prefilter to the shop vac.

Materials:
2 - 5 gallon plastic buckets with lids
2' x 10" round metal duct.
scrap 2x4, 2x6 lumber
sheet metal screws
3" round metal duct
steel wire
3" hose clamp
duct tape
old shop vac hoses and tubes

Step 1: Making the Cone

Layout of the cone was the most difficult part of the build. The longer the side of the cone the better. This design uses and 18" side length from the point to the top of the cone. This size looks to be a nice balance between separation efficiency and total height. The dimensions are shown in the picture. The radius is from a point that is outside of the template. The template does not include the extra metal that will become the tabs on the top and bottom of the cone. There is an extra flap on the template that is used to tie the long seam of the cone together with holes and rivets. Lastly, fit a small pipe to the bottom of the cone. A 3" metal duct would work well. I used a PVC pipe at first, but the thick wall caused material to hang up.

Step 2: Making the Barrel of the Cyclone

The point of the barrel is to start the swirl. This is done by allowing the inlet air flow to happen tangentially. I used an extra 2" plastic pipe from an old shop vac as the inlet to the barrel. Cutting the hole in the barrel to allow the tangential entry was a bit tricky. This is best done slowly to just get the pipe to slip in the hole. The hole ends up looking like a teardrop. Then use some sealant to fill in the gaps. Lastly, the bottom is cut out of the bucket to form the barrel.

Step 3: Attach Cone to Barrel

Use the tabs to attach to the barrel. if the fit is too loose, cut the tabs deeper to allow for a tighter fit to the barrel.

Step 4: Making a Dust Bin

The dust bin is just a bucket with a lid with a hole cut to snugly fit the pipe on the bottom of the cone.

Step 5: Build a Stand

the stand is simple and just made from scraps. The barrel is supported by bolts fitted through the barrel to the wood. I used carriage bolts since the head is smoother and rounded to keep the air flow smooth. The spacer between the wood and the barrel is a 3/4" CPVC pipe 1'' long.

Step 6: Connect With Hoses

Connect the vacuum to the center of the barrel lid with a hose. The hose to collect debris is connected to the tangential inlet to the barrel. One of the pictures shows how much material was collected in the dust bin. Very little material made it through to the shop vac container. Only very fine dust particles were found on the filter element. The last picture shows the dust bin being replaced and how the tilting aspect of the cyclone makes this easy.