Punching Sharp Corners

When punching sharp corners, the cutting clearance should be about 1.5 times normal clearance as shown here.

FORMULA

The following dimensional relationships are what I use to get clean corners while maintaining punch life.

Wire EDM corners

It is possible to accomodate a sharp corner punch with a wire-cut die section by only offsetting the dimensions but that results in tighter clearance at the corner where the punch is most vulnable to rolling over or fracture. You can also predict spikes on your stamped part at the corner resulting from the local compression of the metal into the very locale where you need relief.

The geometry shown above is what I use to get clean sharp corner cuts without spikes and at the same time preventing punch failure at the point where is is most likely to dull first. And as it dulls, the load on the corner increases until finally you have to grind quite a bit off the punch to renew it instead of .005/010.