Started countersinking on ther R-916 training edge. Although I was using a countersink tool, I pressed too hard on one hole and obtained a deeper countersink than set up for and also enlarged the hole a bit. I called Vans and they laughed at me (Ken Scott) saying if that was the only hole I mess up it would be a record. He told me to press on an rivet the thing up. He did suggest manually countersinking and I found with that method I could keep things square more easily and monitor the depth fairly easily.