replying to DoN. Nichols, 42 electrician wrote:
greenlee punches are constant-dimension devices calculated to have a very specific shearing clearance between the mating edges when the edges pass across each other and separate the material. do not grind the parallel surfaces - grind ONLY the top edges ONLY /_*only only. *_/if you grind the parallel edges the shearing clearance will be increased and they are likely to
either give sloppy cut or jam a lot, if they even will cut. as long as the pass edges are fairly sharp square edges ( do not deburr any grinding areas- these edges want to be as microscopically square as possible unless you are cutting HARD HARD HARD material ( 304-316, high carbon) , the shear will cut -
it does NOT need a rake angle. a very small rake angle may help maintain longer cutting action but its a weaker edge. the shear clearance is specific to the gauge (thickness) and tensile characteristics of the metal the device was designed to cut- change the pass clearance and its likely to not work well.
btw- its possible to shrink the outer die but thats another story.
((a shear of this type does not CUT in the conventional machine tool sense - ,
it forces a stress concentration into a very small area and the plastic nature
of the metal allows it to move and separate. this concept is the root of much metal-cutting physics in force-operating tools. )))
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