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Carbide endmill to trim 1/128" off of punch die cavity?

JasonPAtkins

Hot Rolled
Joined
Sep 30, 2010
Location
Guinea-Bissau, West Africa
Hey all, I'm trying to modify an obround die. I know EDM is the right tool for the job, but don't have one available.

I'm trying to get an obround set with more clearance than I currently have (to punch thicker material). I need an obround hole that's 1/4" x 3/4", so I'm using that punch and found a 9/64" x 3/4" die. That gives me the required clearance on the long sides, but no clearance at the two ends. So I'd like to open each end up by .008" (half of 1/64").

I'm considering using a 1/4" carbide EM to bump out, move plus and minus .004" laterally, and end up with a not exactly round end, but close enough for the die.

Presumably the die is hardened D2?

For how little I need to remove, should I just be free-handing it with a die grinder and a stone?

The die needs to be good enough for ~1,000 holes, not 50k.

I could also grind on the punch, but would rather keep the 3/4" and I think it'd be harder to do a good job of that free-hand.

PXL_20211101_105054359.jpg
 

Joe Miranda

Titanium
Joined
Oct 19, 2004
Location
Elyria Ohio
Hey all, I'm trying to modify an obround die. I know EDM is the right tool for the job, but don't have one available.

I'm trying to get an obround set with more clearance than I currently have (to punch thicker material). I need an obround hole that's 1/4" x 3/4", so I'm using that punch and found a 9/64" x 3/4" die. That gives me the required clearance on the long sides, but no clearance at the two ends. So I'd like to open each end up by .008" (half of 1/64").

I'm considering using a 1/4" carbide EM to bump out, move plus and minus .004" laterally, and end up with a not exactly round end, but close enough for the die.

Presumably the die is hardened D2?

For how little I need to remove, should I just be free-handing it with a die grinder and a stone?

The die needs to be good enough for ~1,000 holes, not 50k.

I could also grind on the punch, but would rather keep the 3/4" and I think it'd be harder to do a good job of that free-hand.

View attachment 333499

It seems to me you would need a 17/64" em.
 

AD Design

Stainless
Joined
Jun 27, 2012
Location
Tennessee USA
You could freehand the radii with a die grinder, it depends upon how much allowable burr you want. Don’t forget to add die taper below the land so your slugs don’t stick in the die
 

dgfoster

Diamond
Joined
Jun 14, 2008
Location
Bellingham, WA
It looks as if the die is quite shqllow, like .25” or so. I know you live in a remote area with minimal resources. If all you need to do is remove .008”, I’d consider using a brass lap and coarse diamond (if available) powder or other hard abrasive powder. I have never ground D2 and realize it is very abrasion resistant compared to many materials. But time is on your side and any hard material can be lapped, even diamond.

I have ground lots of holes into glass, files, etc. All you need to do is make a clay dam around the hole, put in some slurry of abrasive and water, and then grind the hole with a soft lap in a drill press or milling machine. It is not fast, but results are controllable. Periodic replenishing of abrasive is needed, of course. Relief of the new hole segment could be produced using a tapered lap to relieve the ends.

But, again, I’ve not done this in D2 specifically. If this idea is unworkable for some reason, I am sure we’ll hear about it.

Denis
 

AD Design

Stainless
Joined
Jun 27, 2012
Location
Tennessee USA
I wouldn't presume the die to be D-2, even if so .008 isn't a lot to grind off. I've ground plenty of D-2 as a die maker and .008 won't be horrible if you don't overheat the die. Dress a mounted wheel to the proper diameter to control the radius and take measurements as you go. Ensure the die grinder is perpendicular to the face while doing this. If you have a surface grinder I would also advise a grind off the face to sharpen the cutting edges. Add die taper below the land, if possible, and you're done. The 17/64 carbide end mill would work also if you have one.
 

Ralph_P

Stainless
Joined
Jan 14, 2003
Location
E. TN USA
I think I'd try the mounted stone with a vertical mill at the highest speed, if it's a manual mill. A Dremel with a cut-off wheel dressed to size might work also. If it's D2 I don't think an endmill will do anything but maybe ruin the endmll and possibly the die.
 

JasonPAtkins

Hot Rolled
Joined
Sep 30, 2010
Location
Guinea-Bissau, West Africa
I ended up using a smaller than 1/4" diameter sandpaper tube on a mandrel on a Dremel. It was slow, and I didn't get everything off that I wanted, but enough.

I will hit the die with the surface grinder once the SG is fixed, but for now a couple of test punches sounded and felt fine (manual bench punch).

I don't think my solution was the ideal, but as they say, "it's good enough for who it's for."
 








 
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