There is a little tool called 'The Digger' made by ??? It is my favorite hinge slotting tool if i don't use Robart hinge points. This little tool looks similar to a miniature pizza pie cutter. You have seen the one with the cutting wheel... On this tool the 'wheel' doesn't actually spin for the 'handle' and 'wheel' are all one piece. Instead of a sharp edge like a knife around the wheel it has serrated (pinked) egdes. I modified mine by bending the serrations alternately from each other slightly out of 'plane' of the handle. It's handle has a slot with a point in the center so that by dragging it across the edge to be slotted you mark centerline. The 'Digger' does exactly what its name states and is the easiest, least expensive, most painless and most accurrate hinge slotting tool I have ever used and I've used the 'slotter'. I think one could easily be hand made and would be worth the effort. I can post a pic if anyone interested.