I had a problem when one of the iron workers tried to use mine. and had the chuck come apart. I was at a show and the rep showed me how to put my old one back together. I have sharpened hundreds of bits with It. When we built a 40 X 120 , 16 ft sides metal building I kept the iron workers in sharp bits and they were very happy. For large drill bits I use an old general sharpener against a 10 inch sanding dist on my combination 6 X 48 belt sander disc combo tool, then manually cut the back relief on the belt sander.