There have been many posts on various web sites asking about "cyclone" trash can lids, making the Wood Mag cyclone (Wood Mag site), and buying a ready made cyclone. I did not think the plastic lid was a good long term value and buying a ready made version was too expensive. I thought about making the Wood cyclone, but after making the list of 101 different screws, bolts, and doodads I would need to buy to follow their directions, I figured there had to be a simpler way. Below is a picture of what I made. I have not put it up against a proper cyclone for a comparison or done any fancy tests of efficiency - but in practice it works well, was very easy to make, and costs no more than a plastic cyclone lid. I'm sure you will have to clean the filter more often than with a "proper" cyclone, but this is easy to do - just run it backwards through your shop vac, or even just run your shop vac attached to a blast gate and thump the top of the cyclone to jar the filter.
I used 30 gallon trash cans which are very close to the Wood cyclone in size. The intake tube was taken from the Wood cyclone. The output tube up the middle of the cyclone is a 10 inch pipe 20 inches long (actually two 5 inch snap-lock pipes used together). Cut a 10 inch circle of plywood, and cut a circle to match the opening in your filter, leaving a thin piece bridging across to hold the 3/8 inch threaded rod that will hold the filter. Screw this circle into the end of the 10 inch pipe and seal. Cut a 6 inch hole or so in the middle of trash can bottom, and bolt the uptake tube in place, making sure it is sealed. Attach a 6 inch to 4 inch reducer to the top of the trash can. You can cut another plywood ring to go around the reducer and screw it in place, or just make cuts in the 6 inch collar, bend them outward to make tabs, and screw through them to attach the reducer to the top of the cyclone. Make sure it is all sealed. The filter is installed open end up, held in place with a wing nut and washer. Make sure the washer is large enough to cover the hole in the filter and fits the threaded rod tight enough that the wing nut seals the washer hole. Make sure the filter opening lines up with the output hole.
Now you need to add a "funnel". I actually used an upside down funnel. This is very important as otherwise the swirling wind will kick up dust from the lower can and the cyclone will do a very poor job of removing dust. If you have a tall smooth can, I think you'd be better off to make a proper funnel inside the can. I used an upside down funnel, with a 4 inch opening at the top and 14 inches across the bottom. I attached a 4 inch PVC end cap inside the opening, and drilled a 3/8 inch hole in the center of the end cap, so that it could be hung from the bottom of the threaded rod that holds the filter. To make the funnel get some roll flashing, 20 inches wide. Cheap flashing is fine and this takes no pressure. Using a scrap strip of board or yard stick, draw a semicircle with a diameter of 15.75 inches (actually 15.65 inches, but let's not get carried away!) and the pivot point at the edge of the flashing. Now draw a semicircle with the same pivot point and a 4.5 inch radius. Lastly, along the large semicircle, starting at one edge of the flashing, measure up 4.25 inches and mark that point. From this point, draw a line to the pivot point. If you cut this out and pull the straight edges together, you get a cone 10 inches tall, bottom diameter of 14 inches and top diameter of 4 inches, but you won't have any over lap to pin it together! So, draw a line inch over from the last one you drew and cut along it instead. Now when you pull it together, but overlap the edges one inch, you can add a few screws to hold it. (Hint, put down a one wide strip of carpet tape along one edge to hold the cone together while you add the screws.) Use a second wing nut to hold the funnel under the filter. This may sound complicated, but is really very easy.
The top trash can just sits on the bottom can, sealed by weight against some closed cell weather stripping. To empty, lift the top and hang on a nail (a hole is drilled in the lip at the top). To clean the filter, just switch the flex tube on the blower to blow back into the top of the cyclone and tap a hammer on the bolts that hold the filter tube in place. I hook a shop vac to a nearby blast gate so the dust does not blow back into the shop. Turn on the shop vac or the pressure will lift the bottom can up blowing dust into your shop. You can also just use the shop vac to suck backwards by itself.
I used 3 layers of plywood to make the connection ring between cans. The top layer has a hole just big enough for the top can to fit into. The middle layer has a hole cut on a bevel so the top is a touch smaller than the hole above, to form a lip for the top can to sit against. The bottom of the middle hole is smaller yet, forming a funnel shape. The bottom layer has a hole with a radius 3/4 inch larger than the edge above, forming a 3/4 inch lip for the weather stripping. The top can went in the top hole, held with screws and sealed with silicone. The weather strip went on the lip underneath the whole thing.
There must be a dozen ways to build a trash can cyclone, at least half of which are improvements. If you want to give it a shot you may want to get the Wood Mag plans, sold for a few dollars by either Wood Mag or by PennState who makes the blower unit Wood Mag (and I) used.
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