If you make it too deep it will catch on the table if you are cutting thin material. The hook I cut at the back edge only needs to be big enough to bite into the back of the material. I made the actual pushing piece from Plexiglas to allow me to better see what was going on. And I also wanted my hand to be protected, so I built a wide base with a handle to allow me to apply pressure to hold the material safely. In designing my push handle I wanted it to be able to hold the material down and against the fence. I wanted a push handle that would always be handy whenever I needed it.
