Homemade Cyclone Dust Collection System

Part 3: Cyclone

by Steve Silca

I have no experience with soldering, welding, or metalwork. So, reading Bill's site and the various links, I determined that I was not going to solder this beast. They spoke of enormous torches and irons that I did not want to get involved with. A friend of mine who works with metal and was familiar with the cyclone style dust collector that I was trying to create suggested that I use pop rivets and epoxy. Luckily, I had a plethora of pop rivets from a suspended ceiling installation, and am fortunate to have a stock pile of West System epoxy and thickening additives.

I used a 4' x 10' sheet of 26 gauge galvanized sheet metal, which I got for $25. Unfortunately, I am dealing with a 7' ceiling height, and even with the motor sticking into the rafters, Bill's ideal cyclone size would not fit. Bill wants a cyclone to have an 18" diameter and a 1.64 cone/length ratio. My cyclone is 17" in diameter with a cone/length ratio of 1.3. The result of this, I think, is that some of the chips that are sucked into the system rotate around the lower part of the cyclone for a while, sometimes until it is turned off, rather than falling right down into the bin. This is not a problem: I have seen no particles in the filter housing, so it hasn't affected the cyclone's ability to separate. But (I think), because of the physics of the air circulating and then going up and out the top, my cyclone seems to suspend some of the chips as they go around the bottom of the cyclone.

Notice seams overlap to create a smooth surface for rotating air and dust inside cyclone

The cyclone went together very well with the aid of a 17" diameter plywood circle. This circle eventually became the top of the cyclone that was fastened to the blower housing. I was also careful to make sure that the overlap of the sheet metal in both the upper cylinder and the cone was oriented in such a way that the air/dust didn't hit a ridge as it rotated around, but rather saw a "ski jump", as Dale Critchlow called it.

Tabs were formed on the cone, and it was pushed over the outside of the bottom end of the upper cylinder. I put the 17" diameter piece of wood at the very bottom of the cylinder during this process which gave the proper shape to the cone and cylinder. Pop rivets were installed from the inside out whenever possible, and I took special care to make sure they were inserted flat and as tight to the surface of the sheet metal as possible. Those rivets that had to be installed from the outside during assembly were eventually drilled out and re-installed from the inside out. I took great pains to make sure that the inside was as perfectly circular and as smooth as possible. All seams, every pop rivet, and every tab was sealed with epoxy from the outside.

The first attempt at an air ramp. Note: air ramp is upside down

The air ramp proved a little more complicated. The picture at the side is my first one. Everything is fine with it, except it spirals the wrong way, and these are not reversible. The way I wanted my ducting to enter the cyclone meant I had to have the directing of rotation within the unit be the opposite of what most cyclones have, and so I had to re-do my air ramp. This one is identical to the one that's actually in my cyclone in every other way: the rivets go from the inside of the 8" outlet pipe to the outside, the tabs on the ramp all are oriented up so they are out of the air flow in the cyclone, and the seam where the ramp meets the outlet pipe was sealed and smoothed with epoxy.

Looking up the cyclone from the bottom. Note: all rivets are installed as flat as possible

The picture at the side shows what the air ramp and outlet pipe look like from the very bottom of the cyclone when they're installed. I was able to reach all the way down with a caulk gun and run a bead of duct sealant around the joint where the air ramp meets the outside edge of the cylinder, which you can see in the picture. I was originally concerned about using 26ga rather than 24ga sheet metal for this cyclone project, which some recommended. Until I had installed the air ramp, I felt that the upper cylinder might be a little fragile and flexible. The air ramp made the entire cyclone much stronger and much less likely to crush (I have run this thing for a long time with all gates closed and neither the ductwork nor the cyclone seem to have been crushed as some said might happen.) In this sense, the air ramp has additional benefit. Not only does it get the air flowing in the right downward direction within the cyclone and reduce turbulence, it also adds strength to the entire cyclone assembly.

Air inlet and transition from round ductwork to rectangular inlet

The air inlet is rectangular, so I understand, because it reduces turbulence in the cyclone by feeding in the air and chips in a laminar fashion. The air inlet transition transfers the round network of ducts to the rectangle of this air inlet. Rather than forming my own transition piece, I was able to find a good HVAC fitting that was almost the perfect size. A little hammering with a ball peen hammer to smooth all the inside ridges, and this piece was riveted and sealed in place. At the bottom of the cyclone I began with a 7" to 6" HVAC reducer, cut off the 7" portion of it, cut tabs, and fit it over the outside of the bottom of the cone. I was able to install the rivets from the inside to the outside, and took special care before I put this piece on to hammer out any ridges on the inside of it that would catch dust or affect the downward circular rotation out of the bottom of the cyclone. This piece was epoxied from the outside as well. I spent a good deal of time making sure the entire cyclone was air tight from the moment of entry to the bottom of the bin.

Finally, the entire cyclone was spray-painted with two coats of machinery grey paint.


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© 2003 by Steve Silca . All rights reserved.
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