Jake is right about the 40" belt/chain. I believe mine is 30". I thought it was wide enough, but it sure is not. I put about 5000 yds through the machine every year. If the material comes right off the truck, it is still loose enough to not bridge. But if the pile has been sitting there for a while and is wet, it's got a hard time to come out of the spreader. Best solution is to load it very fluffy. Haven't tried to load the wet and heavy stuff up front like Jake does, but will give it a try this fall. I'm not sure a vibrator will do the trick. When nothing comes out the back, I usually make a big circle in the field ( driving as fast as I can across the ridges without falling out the sunroof). Sometimes it comes loose, but most times I need to go into the spreader and poke the stuff loose.  Came across an idea today that might work. Gonna paint the inside with a special coat of bathtub and sink paint. It dries fairly hard and is slippery. Will give this a try before I put in the plastic.

About building your own spreader. I have learned that you need to go as wide as possible on the floor. The better ones out there have a square box with a chain running the full width of the floor. Problem with going wider is that you would need bigger gear boxes and shafts. That could run expensive. The wider you go on the bottom, the wider your spinners will have to be. The wider the spinners the heavier they get and the harder to run. Best thing for the spinners would be a hydraulic motor for each spinner. It can handle the jerks a lot better. Since you are moving the whole load you will need a pretty heavy duty worm gear aswell. Most every year I go through at least one worm gear and at least one shaft on the bevel gear boxes. They don't come cheap, but cheaper than bigger gear boxes. 

I based my spreader on a Stoltzfuss lime spreader. Only after finishing the project did I find out that Chandler makes a very similar model to the one I just build. It has the Hydraulic spinners.

If I had to do it over again, I would build one with a wider bottom, maybe even square. Might be more expensive, but less of a PITA. 

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