I've been wanting to build myself a composter for quite a while now. A few months ago some family of friends gave me a bunch of these 15 gallon plastic jugs, so I set about a plan to put them to use. Due to the limited volume (I certainly would have preferred 55 gallon drums), I decided it would be best to incorporate several of them into the contraption to increase output while maintaining roughly the same footprint (maybe something like 2/3s what it would have been if I'd built 3 separate units, anyway). Also, I thought this would be more fun.
Oh, so, a description...
It's a three armed composter. Each arm incorporates an independent composting unit. These arms/units may rotate as a whole as well. The idea being that when one is full it can be shifted back and allowed to cook while the next one is brought forward and gradually filled.
Step 1: Obtain and Modify Your Containers
Right, so, this step, as described, is probably fairly unique to my situation, but it's also very common sensical, so I don't think you'll need to fret much over the details.
Basically, you just need to get ahold of some conatiners of some kind. I got mine from the parents of a friend of mine who were looking for a way to dispose of them. They run a dairy farm and the detergent they use to clean out their milk pipes and tank comes in these jugs. They had 15-20 of them so I took my 10 favorites to start experimenting.
To get these things suspended and spinnable, there needs to be some sort of axle, right? And that axle should emerge somewhere near the center of the both ends of the container. Luckily, the center of the top end of these containers is well marked by a big, black handle affixed with a plastic pin stuck through a little nub protruding from the body of the container. I tried a few different techniques to remove these handles and found that a little limb saw was small and flexible enough to get at the base of the nub.
Once that's cut off I used a "hole saw" on my drill to put a hole in roughly the same spot, corresponding in diameter to the pipe I planned to use for the axle.
Step 2: Building the Hub-arm Rotating Support Apparatus
For this, I started with the hub. I knew I wanted the arms to butt against a central piece, so I worked out this hexagonal shape with 3 sides being 3 1/2 inches, and the others accommodating those in such a way that the hole in the center was equidistant from them, or something like that. Honestly, I don't really remember how I came up with the non-butting side lengths, and I'm not sure they're all that critical. Just seemed like it'd be good to put some space there to give the containers room to fit.
I made "hubcaps" based on the dimensions of the hub, I just added two inches (if I remember right), around the edges and made sure the hole was in the dead center. These were intended to add some lateral support to the arms, and keep them from separating from the hub.
The arms were easy, I just made them a few inches longer than the radii of the containers and put the holes for the container axles about 1 1/2 inch from the ends.
Possibly the trickiest part of the whole thing was trying to figure out the angles for the arm supports and getting my mitre saw to cut them. I ended up just laying everything out on the floor and tracing the angle on the peices to be cut for supports. This worked well enough, but a little additional trimming was often needed for a good fit.
Assembly was pretty easy. I again layed all the pieces out on the floor, lined up the hubcap hole with the hub hole and started tackied it into place. This held everything well enough that I could get some screws into the arms and supports without them sliding around and falling apart on me. Once those were all secure I put the other hubcap on.
This would also be the time to cut your axles. I used two different sources for mine. The central axle was made of some leftover well casing pipe (or so I was told), which was slightly thicker and of a larger diameter than the container axles. The container axels were made of chain-link fence tubing, the smaller stuff that runs along the top, not posts. I think this stuff probably would have been adequate for both axle applications.