Yesterday I decided to get out and replace a hatch port on a dinghy I have listed for sale.  It came with just the ring.  The screw in center disc was missing.  The new port was about a 1/4" larger than the OEM ring.  No problem, I have a Roto-Zip...  The Zip came with a circle cutter that I've never had the chance to use, but it looked simple enough.  The plan of attack was to cut a hole in a piece of plywood and then use it as a guide along with a veining bit to enlarge the hole in the dinghy.  Well... let me tell you... that thing sucks.  I started with a piece of ply about 4' long, and ended up screwing up the entire piece.  But.... I did end up with 5 side stand discs...  And I bet you thought this thread wasn't going to be motorcycle related....