I have been working on a design for a good worm bin and I think I have it all worked out. Here are instructions on building one.
Materials:
at least 1 eventually 3- 5 gallon buckets
1- 12" planter tray, I think mine was marked 11 1/2" but its the one that fits on the bottom of a 5 gal bucket.
2- cinder blocks
1- quart jar or any other jar
Some worms OSH sells red worms in quantities of 200 or you can get them from a fishing supply store. I suggest red worms because they eat compost faster than other worms.
All this can be gotten at any hardware store for about $15-20. I got most of mine at Orchard supply.
Tools:
1/4 drill
3/8 or larger drill
drill gun
Step 1 Drill a 3/8 or larger hole in the planter tray. Best about 2" in from the edge. Arrange the blocks, jar and tray as per the photo. You dont need to use these exact parts but they work fairly well.
Step 2: Drill 1/4 holes in the bucket bottoms. No particular pattern is needed just make a lot of holes. Try not to put so many as to weaken the bucket probably, you could put a lot more than in the photo without a problem.
The way it works. Throw some leaves or shredded news paper down in the bottom of the bucket and put in some regular soil from the yard (worms need the soil to grind plant matter in there stomach) mix it all up about 3" on the bottom is enough. Dump in your worms. Throw in your wast vegetable matter ( if you blend it the worms can eat it faster but its more work.) It takes about a month to double your worm population so dont expect the worms to eat very fast. Start with as many worms as possible (within reason) 1 lb or red worms can supposedly eat 1/2 lb of plant matter a day. When the bucket is 1/2-3/4 full put the next bucket on top.
Put a few scoops of new yard soil in the bucket and then continue throwing in your wast. Continue the process for the third bucket. As the worms eat all the wast from the first bucket they will migrate up through the holes and end up in the second bucket and then the third. When it appears that all the worms have moved out of the bottom bucket (or the third bucket is full) you can take it out and use the castings as the best fertilizer available. Set the now empty bucket on top and continue the process. This setup saves the trouble of having to sift through the soil and dig out the worms. The fluid from the vegetables will drain down through the holes and into the jar. If the bin gets too dry you can pour water on top to moisten and the excess will end up in the jar. This fluid is great liquid fertilizer. If you find your bin getting too dry put a bucket lid on. You may want a lid on it any way to cut down on the fruit fly's that will also like this setup.
You can build this bigger if you want more space. I have a larger one built with a 19" tray and 18 gallon totes. You will have to support the center of the bottom tote or it will break from the weight of the compost, thats what the 1" pvc connectors are for in the photo.
In general surface area is more important than depth in worm bins so the more you have the faster the worms will compost. Any nesting bin would work for this system so imagine away. The one I have detailed here I think should be able to handle the wast from a 3 person household about (1/2 lb a day of wast).
