I figured out how to make a simple doubled side notcher, but still have yet to figure out making a three way one so I can "punch out" a square notch with one push.
The double sided one, I took a popsicle stick and epoxied onto each side, both at the same end, a snapped off piece of razor blade. This way it has a blade on each side, making for a dual cut at once. Looks like a stick sandwiched between 2 blades. Just snapped the blades to the width of the stick.
But you still need to make a side cut to finish the notch.
Now if I can only make a three sided one!
I plan on trying to epoxy a small section of blade in between the two others, but thats a pretty small space to wok with.
The idea would be, one push, cuts a nice notch right out, where you want, and the size you need, nice and square.