Failed Shim Punch Project

[YYCHM]

Image 1 - I attempted to clone a shim punch for punching shims from 8 thou steel shim stock.

Image 2 - A punch set I borrowed to clone. It works quite well.

Image 3 - My first attempt. It produced one useable shim and the proceeded to mangle every one there after.
The ID punch works fine. The OD punch not so much.

Image 4 - I attempted to re-do the OD punch two more times, including lapping the punch to the die using valve grinding compound. No luck.

Soooo, I'm at a loss now as to what to try next. Wrong materials perhaps? I used steel plate and round bar scrounged from the MSM per pound scrap bins. Tolerances not close enough? The die was drilled on my crappy table top drill press, the punches were turned on my 7X12. I milled the die plates with a step rather than using washers to separate the two plates after I got my mill. That didn't help.

Thoughts?

YYCHM

 

[DPittman]

I'm going to guess it has to do do with your drill press. If I understand your project correctly, the hole made with the drill press is the one forming the OD of the shim....drill presses do not make very nice round holes and cheap drill presses are even worse.

 

[PeterT]

I'm impressed you got that far, they look very delicate & fiddly to get knocked out & maintain dimensions without distorting. I've never made them myself but have seen some similar application punch & dies. On those the surfaces look pretty shiny & close tolerances & same for the ram. Wouldn't surprise me if they were hardened & ground but maybe unnecessary for your purpose unless you are contemplating production. Seems to me the punch ID had a coved edge looking from the side & that cutting cylinder somehow stayed inside the donut to stabilize when the OD cut came down. But cant recall where I saw this. Maybe How Its Made show or similar & maybe washers so maybe N/A to your application.

I've seen some model engine guys make head shims as thin as 0.001" using something similar to Joe Pie method below, but they were brass. Another option depending on your pocketbook is laser cutting. I've heard that thin metals can give them grief though because they need to sit flat. You can laminate them to something sacrificial but lasers don't like that sandwich layup because it diffuses the beam on the crack & affects surface finish? You'd have to check but that was my understanding.

 

[YYCHM]

"I'm going to guess it has to do do with your drill press. If I understand your project correctly, the hole made with the drill press is the one forming the OD of the shim....drill presses do not make very nice round holes and cheap drill presses are even worse."

Would my mill do a better job of cutting the ID/OD die holes?

The shim ID is 11/16 and the OD is 7/8. The punch set I cloned was crafted by a tool and die maker and show it.

 

[kevin.decelles]

I splurged some time back and went with the Precision true-punch set like this one from KBC tools Precision tru-punch. I can't recall paying over 300 for it though.

I use it mainly to cut shims for old machinery. Very slick. The interesting part is that the punch itself is made of tool steel, but the top of the guide block is some form of plastic/acrylic on a metal base. Extremely tight tolerances on everything.

I bought it after years of butchering shim stock with everything from scissors to snips to utility knife etc. Next I started ordering pre-cut shims from Fastenal, and after a couple of orders, just bought the machine and buy my shim stock in rolls/flat sheets.

Still cheaper than the machinist hammer I made at SAIT though.

 

[YYCHM]

The shim ID needs to be 11/16 and the OD 7/8 or there abouts. I don't think a universal shim punch will cut that, also, not prepared to spend more than $100 on this project. A tool and die maker already quoted me $300+ to build one.

So, can I make this work or not? I'm already into it for $50 worth of materials but willing to give it another go if it's feasable.

 

[Dabbler]

So here is how I'd make them on my lathe. I'd superglue the shim stock to the end of aluminum bar stock. turn the OD. then with a sharp HSS tool trepan the ID. torch, and the shim is free. Reface the end of the bar stock. repeat.

 

[YYCHM]

So here is how I'd make them on my lathe. I'd superglue the shim stock to the end of aluminum bar stock. turn the OD. then with a sharp HSS tool trepan the ID. torch, and the shim is free. Reface the end of the bar stock. repeat.

The point of using the punch set is to repeatedly bang out a 1/2 dozen or so shims on short notice. What you're suggesting is way too time consuming.

 

[John Conroy]

I think the holes in the plate need to be bored using a boring head on your mill. They need be as close to zero clearance with the male punch as possible or the thin shim stock will just fold instead to shearing.

 

[YYCHM]

I think the holes in the plate need to be bored using a boring head on your mill. They need be as close to zero clearance with the male punch as possible or the thin shim stock will just fold instead to shearing.

Zero tolerance was what I tried to accomplish by lapping the punch to the die. Perhaps the lapping just exasperated an out of round problem? Is tool steel required for this application? Note the guide pins on the punch set I attempted to clone. Would that be a key element in this puzzle?

 

[John Conroy]

I think you're right. Lapping can only make a hole larger so that's not the answer. If you're going to use it a lot then mild steel is not the material to use. The alignment pins would make for consistant function of the tool I think. How big are the plates? I have a round log of 4340 tool steel 6.75 inches in diameter. If you want a couple of slices from it let me know.

 

[Dabbler]

YYCHobbymachinist, I went back to see how many you were going to do, and didn't find a quantity....

There's a technique used in commercial punch and die sets, where the punch has both diameters built right in, where you take materrial, punch the inside hole and it says on the punch and the second shoulder is for the outer cut. the die is aligned in the second case by boring a clearance cavity and leaving an alignment hole at the bottom of the hole.

If you are remaking your punch set, this might help.

 

[YYCHM]

I think you're right. Lapping can only make a hole larger so that's not the answer. If you're going to use it a lot then mild steel is not the material to use. The alignment pins would make for consistant function of the tool I think. How big are the plates? I have a round log of 4340 tool steel 6.75 inches in diameter. If you want a couple of slices from it let me know.

Two 1/2" slices would suffice for making the die plates thanks. I'll PM you.

Any idea where I can source 1" round stock tool steel. Need two pieces 4" long. MSM only lists drill rod when you attempt to quote on-line.

 

[YYCHM]

YYCHobbymachinist, I went back to see how many you were going to do, and didn't find a quantity....

There's a technique used in commercial punch and die sets, where the punch has both diameters built right in, where you take materrial, punch the inside hole and it says on the punch and the second shoulder is for the outer cut. the die is aligned in the second case by boring a clearance cavity and leaving an alignment hole at the bottom of the hole.

If you are remaking your punch set, this might help.

Sorry, me bad, should have mentioned quantity in my OP.

As for this other technique, do you have an image or a link to such an arrangement. I'm having a hard time getting my head around how that would work.

 

[YYCHM]

I think the holes in the plate need to be bored using a boring head on your mill. They need be as close to zero clearance with the male punch as possible or the thin shim stock will just fold instead to shearing.

Would the holes need to be bored or would plunging the appropriately sized end mills into the die plates suffice?

 

[Dabbler]

I'll do up a drawing later today. the hole has to be bored, not milled for accuracy and concentricity. Neither is likely when just plunging with an end mill - sure you can hole to a thou or 2 on an accurate bore by plunging, but that is unlikely to be good enough is the shim stock is very thin.

 

[PeterT]

Drill rod is dimensionally pretty decent tolerance & finish. It can be machined in its stock (annealed) condition as it arrives & then hardened & quenched, which is exactly what its intended for. I suppose you could locally heat the end only, quench & temper, depending on your resources. I have done smaller stuff with torch & oven to temper. It typically comes in 36" lengths in rounds. Here are some prices from KBC. A=Air W=water O=oil. Unfortunately, not exactly cheap in that larger diameter.

 

[Dabbler]

Sorry my CAD program is buggered... I'll have to draw it by hand and send it to you. Too busy right now, but soon.

 

[YYCHM]

The hole has to be bored, not milled for accuracy and concentricity. Neither is likely when just plunging with an end mill - sure you can hole to a thou or 2 on an accurate bore by plunging, but that is unlikely to be good enough is the shim stock is very thin.

Would a reamer do the job?

Where does one find a mill boring tool for something 11/16 to 14/16?

 

[Dabbler]

OK got it running again - gotta love Windows 10!



Any boring head that will fit your mill will do.