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View Full Version : Presshear, hole punch question.



daveo
06-16-2019, 01:09 PM
I bought a old Bateman presshear #10, the guy that had it, didn't know much about it. The hole punch itself was broke off but it was a 9/32 punch and a 5/16 die. This probably isn't right, anyone?

I can buy new ones or even make some. I'd like to know if there was any science behind that combo or just wasnt matched correctly.

LKeithR
06-16-2019, 01:20 PM
A 9/32" punch with a 5/16" die is right. Rule of thumb is that for any material 3/8" and thinner you
need 1/32" clearance; above 3/8" you should go to 1/16" clearance. And normally you don't punch
holes that are smaller in diameter than the thickness of the material...

daveo
06-16-2019, 01:26 PM
A 9/32" punch with a 5/16" die is right. Rule of thumb is that for any material 3/8" and thinner you
need 1/32" clearance; above 3/8" you should go to 1/16" clearance. And normally you don't punch
holes that are smaller in diameter than the thickness of the material...

Thats good info! Thank you!

daveo
06-16-2019, 07:27 PM
Another stupid question, was this cutting a 9/32 hole or 5/16?

LKeithR
06-16-2019, 08:21 PM
Another stupid question, was this cutting a 9/32 hole or 5/16?

The hole will be 9/32" (or very close). It's the punch that determines the hole size; the die is over-sized
to provide the correct clearance for the application. The hole will be very close to nominal size on the front
face of the material but tends to be slightly larger on the exit side...

Tim The Grim
06-16-2019, 11:31 PM
Different metals require different clearance. That being said, the character of your hole or slug will determine how you want to calculate the clearance youíll use for the result you wish to obtain. Yes there is a science to metal stamping and it could fill volumes. Iím sure theyíve been written about most of the materials designers pull from a list when theyíre specing out a bracket or framework for some assembly.
Itís the oddball stuff that gets really fun to play/experiment with when youíre building tools that push the envelope.
I built a lot of dies that punched holes that were smaller than the thickness of the material. We wanted the slug, not the holes. Kind of extruded with minimal break. Squishy exotic electronic alloys for semiconductors and the like. If you had a TI calculator built between Ď76 and Ď85 my stuff is in there. I actually did that kinda stuff for 15 years altogether. Still miss the challenge proofing out a new tool.

Clearances generally run between 5% and 12% (per side) with the tougher, higher tensile strength alloys needing less and the softer chewy stuff more. You can tune your punch/die combination to get more or less shear/break by using a different clearance. Even the speed of your press stroke can vary your results.

I bought a 5 ton Benchmaster press for when I retire and get the urge to build some small stamping dies. Iím not yet sure what, but Iíve got some ideas.

Have fun.