The problem of determining the life of the bearing seated in the wood is an interesting one. The stress on the wood is only a few hundred psi, and there should not be too much motion between the bearing and the wood if the bearing is doing it's job. The fit of the bearing into the wood is also interesting, it would be nice to have an interference fit, but it would probably be OK to have a slightly loose fit. I did a quick experiment yesterday, I looked around in my home shop and found a 1-1/8" hole saw, and cut a hole in a piece of 1x6 red oak. I went to the hardware store and bought a couple cheap bearings, and put them in the hole, and put a 1/2" bolt through the bearings. There seems to be a couple thousandths of an inch clearance between the bearings and the wood hole. Playing with it, it seems to be pretty darn durable. I guess it would need to be turned into a robot and tested by students for a few days to get a better idea of how it would last, though.
