There are two basic ways to compost outdoors, a static bin (like the one my colleague David Priest made himself) or a compost tumbler.
There are(plop down a bucket -- done!), but even if you follow Dave's more involved design, it has a downside. Static bins are easy to set up, but they need more work to maintain. If, like me, you're more of a "long-term lazy" type, the tumbler-style composter may be for you.
In order to decompose evenly and help reduce the likelihood of attracting unwanted pests, your compost needs to be turned regularly. With a static bin, that means taking a shovel or a pitchfork and manually digging through and turning the compost. With a tumbler design, you get to live out your wildest dreams as a contestant on The Price is Right spinning that big wheel. Just grab the edge and let it rip. Your prize will be rich planting soil that's easier to maintain.
These directions will make a tumbler that's 3 feet wide and about 20 inches in diameter, for a potential of about 6.5 cubic feet (or just shy of 50 gallons) of compost.
If you already have the tools for the job, you're looking at an overall cost of about 60 bucks. You can compare this to off-the-shelf options of 50- to 100-gallon capacity tumblers ranging in price from $100 to $300. You'll have more options for the actual size and look of the finished product, plus that sweet, sweet feeling of accomplishment.
Materials list: eight 6-foot two-by-fours, two 2-by-2-foot panels of 3/4-inch plywood, two 10-foot rolls of galvanized steel hanger straps, a bunch of 1-1/4 inch wood screws, a 4-foot piece of 1-inch galvanized steel pipe, a set of hinges and a latch.
Tools list: Measuring tape, power drill, 1-3/8-inch spade bit, saw (circular or miter), brad nailer (optional).
Step 1: Cut the body
First, take the eight two-by-fours and cut them in half, leaving sixteen 3-foot pieces. Then take three of those pieces and cut them in thirds, giving you nine 1-foot-long sections. Now, lay out all the boards, making a rectangle three feet wide by the width of sixteen two-by-fours (56 inches) with the three pieces that you cut into thirds somewhere in the middle, seated next to each other.
Step 2: Connect the boards
To secure the boards, I went with thin, flexible metal straps that you can attach to each board with wood screws. Lay down one strap about 10 inches down from the top edge, and then another 10 inches up from the bottom edge. Leave 6 inches of strap hanging off of one end of both straps. You'll use the extra strap to secure the tumbler shape in place. For best results keep the boards as snug to each other as possible, and on each strap use two screws on each two-by-four for a total of four screws per board.
Once you've secured the first two straps, take two more 18-inch pieces of strapping and connect the three, 1-foot pieces on either side of the access panel to each other and to their neighboring longer boards. With these, come in about 2 inches in from the top and bottom edges of the whole assembly. You'll secure the three foot-long pieces in the middle for the access door in another step.
You can now take board assembly and stand it up on one side. Keeping the strapping to the inside, pull the two ends towards each other, to form a cylinder. Pull everything together nice and tight and screw down the overlapping straps.
Step 3: Attach the side panels and make the door
Now, on to the plywood. Drill or cut a 1-3/8-inch hole in the center of each plywood panel. The easiest way to find the center point is to draw two lines, going from each corner to the opposite corner. The point where they cross is the center point. I also took this opportunity to use the center point and draw a reference circle on each piece of plywood for placing the tumbler body. A diameter of 20.5 inches was perfect for me.
Once you've drilled the center hole, take one of your plywood pieces and center it on top of your upright cylinder. Screw through the plywood into each board end. I used a brad nailer to hold the boards in place, then added screws after. Flip the assembly and repeat for the other end.
If at this point you have what looks like the world's worst homemade TIE fighter, you're headed in the right direction. For extra strength, I cut two pieces of two-by-four that are 3-1/2 inches long (making them 3-1/2 inches squared) and drilled one 1-3/8 inch hole in the middle. I secured one to each end, lining up these holes with the ones in the plywood. This will help prevent wearing out the plywood when you're spinning in the Showcase Showdown.
To make the access door, line up the three foot-long sections and secure them to each other using two 10-inch-long pieces of strapping, about two inches from the top and bottom edges. On the nonstrapped side, add the two hinges to one of the boards, about 2 inches from each end. On the other non-middle board, center and add your latch. Now take your door to the tumbler assembly and hold it in place. Secure the hinges and latch receiver to the tumbler body. After making sure your door works correctly, take two more 10-inch pieces of strapping and add them to the outside of the door, each centered between the hinges and center latch. This will help the door to keep its curved shape when you open and close it.
Final steps: Customization and mounting
You have options for the overall dimensions of the tumbler. You can cut the boards that form the body longer or shorter as desired. You can also change the number of boards you use overall to adjust the diameter of the bin.
I would advise against using boards that are wider than 3.5 inches (standard two-by-four width), as your tumbler would start to become more square-ish and defeat the more-efficient mixing capabilities inherent to the cylinder shape.
If the weight of the bin is an issue, you could get away with using one-by-fours if you add a couple of metal strips around the outside of the tumbler as well to reinforce them. That would cut the overall weight nearly in half.
The gaps between the two-by-fours should prevent the need to drill holes for air circulation as you might normally need to do for other types of tumblers. If you end up with too much of a gap between boards and you feel that you're losing too much material when you spin it, just staple some fine metal mesh inside the tumbler body over the problem areas.
To make this a permanent installation, I'd suggest using two 6-foot four-by-fours for mounting posts. Bury about 30 inches in the ground, set with concrete, then drill a hole in each of the posts for your galvanized pipe. Slide your pipe though the holes in the tumbler and each of the posts. Add pipe caps to the ends of the pipe and you're set.
For a long term setup, consider treating the tumbler with a dark colored paint/sealer combo. The dark color will help absorb and retain heat, which is more efficient for the composting process. The sealant will give your tumbler a longer lifespan, fending off deterioration from weather and related moisture.
I wanted my tumbler to be movable, so I made a sawhorse-based mounting frame. I picked up two sets of sawhorse brackets for five bucks each and used five six-foot two-by-fours cut in half to make the legs and bridge. I added a 1-1/4-inch PVC coupler held down with a 1-1/2-inch pipe strap centered on each sawhorse. Now you can run the 4-foot piece of galvanized pipe through one of the PVC couplers, then through each drilled hole in the tumbler, and again through the coupler on the other side. I also added a pipe cap to the ends of the galvanized pipe to help keep it from sneaking out of the couplers.
An afternoon's worth of work and you have your very own compost tumbler! Give it a few spins a couple of times a week and you're good to go.