Trommel Compost Sifter

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Introduction: Trommel Compost Sifter

This Instructable shows how to build a trommel (rotary screen) for sifting compost or shredded leaves. The purpose of sifting is to separate coarse unfinished compost materials from the finished product or to separate out trash and debris from other organic materials before use in the garden. My city has trucks that go around sucking up all the leaves in the fall. These leaves are then placed in a huge pile and allowed to decompose. I can go get decomposed leaves from them as needed but they often contain trash and rocks that need removed so I'm planning to use this trommel to sift that material as well as compost. Sifting also makes organic materials appear more uniform which is desirable if you are using them as a top dressing or mulch.

Step 1: Materials

Materials needed:

- 1/2 inch hardware cloth
- two large surplus bicycle rims
- 4 rollers and bolts to attach
- a little over 8 feet of dimensional lumber
- misc. wires for connecting the hardware cloth to the rims

Step 2: Remove the Spokes From the Rims

The fastest way is to cut them if you have some really strong wire or chain cutters. I used a really ancient fencing tool and that worked great! NOTE: You may also want to save the spokes to make plant markers.

Step 3: Cut the Hardware Cloth to Fit Inside the Rims

My rims (inside) measured about 21.4 inches in diameter so multiplying 21.4 x pi gives me a 67.2 inch minimum length. Add about 4 inches for overlap of the seam and cut at about 71 inches. I used standard 36 inch width hardware cloth.

Step 4: Attach the Hardware Cloth to the Rims

Place the hardware cloth inside the rims and attach with wires through the spoke holes. I used plastic coated #14 household electrical wire. To fasten the seam of the tube I used #18 wire. (Be careful not to over tighten the wire or the wire will break.) Make sure the wire on the outside of the rim is lying flat so that the rollers don't bump over it.

Step 5: Build the Roller Box

This is a pretty simple structure so I won't go into a lot of detail. I used 2x6 lumber because I happened to have several short pieces on hand that were just the right size, but 2x4s should work fine too and would be a little lighter. My side pieces are 34 inches long and the ends are 19 inches long which leaves a gap of 16 inches in the middle. Note that one end needs to be ripped down 2.5 inches lower than the other because the drum needs to overrun the box slightly so that the coarse materials spill out of the drum. Since I used 2x6s (1.5 x 5.5) my spillway end piece was 3 inches wide. If you are using 2x4s (1.5x3.5) Then your end piece would need to be one inch wide.

Note that these dimensions assume that you are using the same diameter rims that I used. If you use different size rims then obviously you will need to modify the dimensions to accommodate your particular arc.

To align your rollers place the finished drum onto the roller box and then mark your roller positions. You may want to attach the rollers first with simple drywall screws (as I did) to test their positioning and then drill and bolt them later once you are happy with the alignment.

Step 6: Done

Once the roller box is complete you are ready to try the trommel out. Mine fits perfectly on top of my wheelbarrow which is handy so you may want to take your wheelbarrow size into account when planning your dimensions. You could also place the trommel on sawhorses or make permanent legs if you prefer. Just make sure the output side of the trommel is slightly downhill from the input side.

If you have a large quantity of material to screen you may want to find a buddy who will keep turning the drum while you continue shoveling jmaterial. If you are working alone then you will have to load a couple shovelfuls into the drum and then give it a few turns yourself before loading more compost. Or if you are really mechanically inclined you could figure out how to hook up an electric motor like this guy did.

Step 7: One More Detail

Once I tried the trommel out I discovered that if you pile a couple shovelfuls of material in the uphill end of the drum and then turn it yourself some of the coarse material tends to spill uphill and out of the drum. To solve this problem I made a simple partition out of plywood to prevent this from happening. I don't think this would be a problem when operating the trommel with a buddy since the material wouldn't build up into such a large pile as you have when working alone.

2 People Made This Project!

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45 Discussions

To make this easier to scale to different rims etc.

How many radians is the distance between the two rollers?

As my current build is approx. 30" rims and 36" long 1/4" hardware cloth.

1 reply

I experimented:

The best distance - gives the best combination of support and stability - is whatever puts the supporting wheels so they are about 90 degrees apart on the rims. If you draw lines from center of trommel through the axle of the support wheels, it should be a right angle.

Closer together and the trommel is top heavy and falls off easily when you spin it with a full load.

Farther apart and it tends to be harder to roll.

Has something to do with vectors of force and the fristion and that's out of my security clearance area.

If only it could be pedal powered, then that would be much more efficient energy wise.

I love this!!!! Made a flat box sifter at home, but I think I'll use this idea for the kids at the Boys and Girls Club :)

Wow, that's really awesome! It looks like it might be a bit awkward to retrieve the sifted fines from the drawer. Have you considered designing it so that the fines would drop directly into a wheel barrow or your tractor bucket? By the way, what is the device shown in picture 100_1360? ( http://steveandlizthompson.shutterfly.com/88#114)

This trommel exceeded my expectations. It was easy to build, and is MUCH easier to operate than my old compost sifter. Compost can be sifted as fast as it can be shoveled in.

With an assistant, I was able to sift about 8 cubic yards of compost last weekend. In two more weekends, the entire pile (35 feet long and 15 feet wide) will be sifted. Everyone with a sizeable compost pile would do well to build one of these.

Incidentally, I added 2 aluminum strips (about 1.5" wide, with an "L" profile) to the inside of the screen, to help lift compost as the drum turns. But I don't think these pieces made much difference.

1 reply

Fantastic Instructable! I just made my own, fitted to the top of the empty third section of my compost bin with recycled bed frame wheels. Thanks so much for posting, it has already saved the strain on my back!

I've made this and love it. I love it, the compost loves it, my back loves it, the neighbor kids love it. I used 2x3 from Lowe's because it's way less expensive and I enjoy the "weathered" look that the frame has. Also had to use swivel casters due to no rigid casters available at the time. They still work if they're pointed in towards the wheels. Zip-ties were used instead of wire but it does make it quite bumpy on account of the locking end of the tie lies within the groove of the rim. I think this helps a little by jarring the load every few degrees of rotation, however I reused the rim liner and this has reduced the bumping a bit. I told my dad about it and he wants to build one too. Maybe I'll expand on this idea some. Great 'able, thanks!

4 replies

"but it does make it quite bumpy on account of the locking end of the tie lies within the groove of the rim."

Try putting the locking end on the inside instead of the outside.

Yeah, I totally had to redo all the ties that way. Still works super though but I need to make up a feed-side hopper.

Very late posting a thanks, but thanks. Well written and a nice idea. I came across a non-functional wheelchair. The handrims make for a nice way to rotate the device and keep the material turning inside a little longer, which I find beneficial. Yours is the first instructable I ever built. Thanks again for sharing your idea. The supports are two simple Aldo Leopold benches that have many uses. Plans can be found by searching "ALDO LEOPOLD BENCH". I found them here:
http://www.epa.gov/greatlakes/greenacres/wildones/wo27bench.html

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Excellent Instructable. Consider unscrewing the spokes from the rim rather than cutting them. Ends are not a sharp and less metal is lost. The inside of the rim should have a spoke holder that you can unscrew with a slotted screwdriver.

I used tin snips, ant they worked well!

I also found free bike tire rims from a local bike co-op. They also suggested the local metal recycle business for free bike tire rims.

I got 26" rims free. (24.5" inside diameter for 77" hardware cloth minimum length)

Thanks for this well built instructable. (I always want to read this as Indestructable!)