We would save the cobs from shelling corn for the pigs and 1-2 times a year would grind then for using on the barn garage floors. ( we ground cob and all for the cattle). Corn cobs are soft and very absorbent. In order to grind well they need to be dry. Its a very dusty job. They will break down over use also. We used corn cobs and a light oil to polish injector parts and press stampings for carburetors. Ran 24-7 with these harder heavier parts in the cement mixer type polishers they would be much finer when they were discarded. The grinder we used was pto driven and ran from a 50 hp tractor. The grind wheels could be set down to grind flour from wheat if desired. ( Dad occasionally planted an acre or 2 of buck wheat and we ground that into flour)