My brother is a grain farmer and asked me to make him a small hand powered grain grinder. He says he wants to test different types of grains for their ability to be ground. I didn't bother to ask any more as I figured he knew what he wanted. I took his specifications and below are pictures of the grinder I made.
I forgot to put a ruler in the picture for a scale but the large gear has a 4" diameter and the small gear has a 2.2" diameter so you should be able to get some idea of the size. The two gears drive the rollers at different speeds so there will be a shearing and rolling action of the grain and not a crushing action. The ratio of the speeds of the two rollers is 1.843 to 1. The two rollers are 3" in diameter and 6" long and mounted on sealed roller bearings. These rollers are placed so there is 0.045" clearance between them and have been knurled to give a better grip on the grain. The legs can be moved to a storage position so the grinder will take up less space when not in use.
This was my first attempt to make gears and it only took three gears to get two good ones. Not bad for the first attempt!