I have both made and purchased bevel mat cutters. The key difference I discovered is that mat board is pretty delicate, and you need a very smooth and fairly broad sliding surface. You don’t want to leave shiny lines from pressing down hard and sliding and you don’t want to leave tears or embossing. The amount of force it takes to cut through good quality mat board is also higher than I expected and a few of my less well thought out attempts ended up with the knife pulling out if its holder and getting stuck in the board.
I threw out all my homemade ones and got one of these cheapos http://www.dickblick.com/products/dexter-mat-cutter/. It works pretty well and is less expensive then screwing around and wasting mat board.
