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:
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Some of my Greenlees are probably 20+ years old now and the cutting
> sections have become dulled. These are expensive boogers to just
> toss out and replace, so how can they be resharpened?
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to which I replied:
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Well ... *I* would try grinding back the points and edges on the
> punch -- on the inside, not touching the outside. I suspect the points
> to have experienced the worst dulling I would probably use a die grinder
> for the purpose -- either one powered by compressed air, or an electric
> one, with the punch held in a vise, or bolted down to the workbench by a
> screw into the dive screw hole.
>
> If the edges in the die are also rounded, you've got less meat
> to grind back there -- but I would do *that* on a surface grinder to
> make sure that it is evenly reduced all the way around.
>
> Note -- as you grind back ether, you will be increasing the gap
> between punch and die -- and thus possible burr from the punching
> operation. This is because both punch and die are slightly tapered, to
> keep them from binding in the workpiece.
>
> If you want, I can post the question on rec.crafts.metalworking,
> and try to gather it all together for you. Be warned that things are
> likely to drift off topic.
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And his latest return is:
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I think that what he's really interested in is knowing what kind of
> shop he might take it to to get it sharpened. He's an electronics
> tech, not a machinist. Remember R & M Saw and Tool around the Navy
> Yard? They would probably know what to do with it, but I don't know if
> there are shops like that any more. He's in Oklahoma City.
>
> Toss it out to the Metalworking newsgroup and see what happens.
> Suggest that someone might know of a sharpening service that's smart
> enough (with your excellent analysis) to know which end to blow into.
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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.
Reply to
DoN. Nichols
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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
Reply to
DanG
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.
Reply to
DoN. Nichols
Since OKC is a good size city, have your friend look for tool and die makers in the phone book.
Reply to
Roger Shoaf
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. )))
Reply to
42 electrician
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. )))
Reply to
42 electrician
The OP was 16 years ago.
Reply to
Michael Terrell

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