Our community intalled ground based fiberoptic broadband last year, leaving big, empty cable drums around. So I asked nicely could I get them. Two of them were not made in the "traditional" style of drum, so after a couple of weeks of just looking at the structures, I felt I had a somewhat clear picture in my head how to make a compost tumbler.
Step 1: The Walls
What I wanted was the sides (se picture of one of the drums being fully dismantled) to function as walls/lids, so on the other drum (not yet dismantled) I removed half of the boards making up the inner core. I needed to keep the shape for the next step.
Step 2: The Roof
First of, I used a staple gun to fastened a layer of black weave weed protection barrier (not being too airtight), prior to making the roof. Then I nailed cut boards from longer ones (and also used the boards from being left over from dismantling) to make the curved roof. Not covering the entire surface, I left an opening for the hatch, were loading and unloading of compost material and ready to use soil would happen. Lastly, I removed the rest of the boards making up the inner core, since the structure now was secured.
Step 3: Insulation
To keep the heat from the chemical process inside the tumbler, I bought eight pieces of styrofoam insulation sheats 1200X600X70mm (about 46x24x3 inches), meazured and cut them in sizes with a sharp knife, to cover the inside of the "walls" and the "ceeling" (inside of the "roof"). To fasten them firmly I used foam insulation. I also used the foam to plug gaps where water or insects otherwise could penetrate.
Step 4: Finishing Tasks
Sorry, but I forgot to take pictures making the tumbler stand (STURDY stuff!) and the hatch (door), but I hope you can see in the picture how I went about :-(
I used a piece of old self made flag pole (made from pine) for the rotary suspension. The pole glides on a plastic tube (an old roadworks sign) attached to the compost wall holes. Actually, the tube was such a perfect fit, I had to use a large mallet to get it through the holes. So it sits quite firm.
I covered the walls with thin plywood sheets, fastening them with outdoor wood screw.
Lastly, I used three thick layers of white alkyd primer (oil-based) to make the compost resistant to moist and rain. No other paint required (I think..?).
Ps. If you try this, be prepared for a lot of custom cutting to fit each piece of styrofoam, especially around the hatch opening, so it closes firmly.
Step 5: Upgrading and Future Problems
Having the capacity to contain 400 liters of material (about 14 cubic feet), I'm now looking for a way to install some kind of lever device, to easily revolve the quite large compost. Being filled up, it may show hard to do just that.
The styrofoam faces the inside "naked". When being filled up, there will probably be some form of wear and tear, causing crumbs or pieces of styrofoam ending up in the compost. I may have to prime/saturate the styrofoam surfaces with...well, maybe plastic paint, or some sort of resin..? Any better idea out there?
NOTE: I still haven't used the compost. Instead, I keep it outside to see how it manages all the Swedish seasons. Four months and going (now december), it has managed the wet autumn; not one singel drop of water or insects have "broken" in to where it all should happen. Also, it doesn't seem to be too airtight, producing moist, or letting through too much air, freezing up. Great! :-)