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Die clearanace, punched holes.

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T Bredehoft

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I'm in need of replacing some hole punch dies. I understand that the clearance of the punch is a function of the thickness of material punched, but have lost the information. I'm punching both .098 and .328 holes in .015 shim steel. (two separate holes, resulting in a washer.) What is the percentage of .015 than I need to make the punch smaller than the hole in the bottom die?

I know exactly what I need, hope I've explained it above.
 

Ed ke6bnl

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just for an idea, I have a 9 piece punch and die kit by TruePower #444 that is manual for thin material and the 3/8 punch is .373 for a hole of .374, the 1/8 has a .125 hole and and .1235 punch.
 

Tinkertoy1941

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Punch determines hole size
Die determines blank size
10% equals normal clearance per side
Punching .015 thick shim stock I would 5% for a clean cut
Reply for more info
 

mmcmdl

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Smaller things as those we always used the 5% method . We would bore the die in a BP and just install a punch in the spindle . These were small lot runs for R&D .
 

pdentrem

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On .015”, clearance per side would be .00035-.0004 for a total of .0007-.0008” . Appears that the punch is not centered thus too much clearance on the side that tears.
 

BGHansen

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Some variation of opinions out there, but most recommend about 20% of material thickness total clearance (diameter minus diameter) for mild steel. Use 15% for aluminum and 25% for stainless. Link to an on-line clearance calculator is below. The harder the material, the more clearance needed. I'm thinking your shim stock will be pretty hard, so you'd want close to 0.004" clearance.

Bruce

https://www.unipunch.com/support/calculators/die-clearance-calculator/
 

P. Waller

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If the customers require a truly clean edge you should look into fine blanking.
 

pdentrem

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Food for thought.

We regularly stamp .010” to .020” Kovar and Alloy 42 lids and we use very tight clearance on all our dies. If not, we have to tumble longer to remove the burr. There are times we use a shim die, where a die is too loose making for a large burr, by placing a piece of hardened shim stock that is thicker than the finished part. By stamping the shim and then afterwards the lid material, we have a better part. Naturally the shim is fixed in position through the whole process.
 

derf

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Normally on mild steel the clearance is 10% of material thickness.
 

T Bredehoft

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The punch is mounted on the arbor of my one ton HF arbor press, the cavity on the base. the only 'guide' is the cavity itself. I have the arbor shimmed so there's ho shake, but it's not precise, just works.
Thanks for all the help, I'll be making a couple of punches probably tomorrow. O1 drill rod, heat to red, quench in oil, anneal at 450 in the oven.

Thanks for all your help, I'll print this out so next time I'll have it on hand.
 

4ssss

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The blanks we ran on an eyelet machine were also cut on a scalloped die to shear them
 
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