On Sunday, October 10, 2021 at 4:18:06 PM UTC-4, 42 electrician wrote:
> 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. )))

The OP was 16 years ago.