Sharpening Greenlee chassis punches

RCMers,
    I've recently gotten a question forwarded to me by a friend on a mailing list. The original question was:
=====================================================================> Some of my Greenlees are probably 20+ years old now and the cutting

====================================================================to which I replied:
=====================================================================> Well ... *I* would try grinding back the points and edges on the

====================================================================And his latest return is:
=====================================================================> I think that what he's really interested in is knowing what kind of

====================================================================    So -- any suggestions (including corrections to what I suggested)? I'll try to bundle up everything which comes back reasonably on topic and pass it on. In particular, suggestions of who could do the task in the Oklahoma City area would be welcome.
    Thanks,         DoN.
--
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Franz tool would be the best place to take the units for sharpening. They are located just west of the Red Dog on NW 10th west of McArthur.
Their specialty is saw blades, but if for some reason they can't work on the punches, I'm sure they will know a place to send you.
(top posted for your convenience) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net
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    Thanks! I've passed it on, and hopefully when it reaches the end of the chain we will have a happy chassis punch user.
    Again thanks,         DoN.
P.S.    A lot less in the way of responses than I expected, but this     looks like a good one, which is what matters.
--
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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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Since OKC is a good size city, have your friend look for tool and die makers in the phone book.
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
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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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On Sunday, October 10, 2021 at 4:18:06 PM UTC-4, 42 electrician wrote:

The OP was 16 years ago.
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