I am currently having my one busy that goes to my trade school for machining (I go for welding) make me a cold working punch with interchangeable centers I designed the entire thing in CAD and made drawings for him (I will put the drawings in here later) i currently have a center punch with a sixty degree tip that I am going to harden and I have a I don’t know how to describe it it is almost a pin punch but they are half an inch in diameter I am having him make me one insert made of aluminum, one of brass, and one of steel that I am going to harden 

I am having him make me two of these as I plan to give one to my dad as a gift my question is does anybody have any other suggestions as to what inserts would be good to have?

Edited March 19Mar 19 by Mod34
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How is the interchangeable bit held in place? This could be a useful tool if it doesn’t put too much stress on a set screw or screw system. One punch fits all?

12 minutes ago, Ridgeway Forge Studio said:

How is the interchangeable bit held in place?

The inserts have a quarter twenty thread turned onto them that thread into the body and then the body has a set screw that will register against a flat spot I will file onto the threads 

in around an hour and a half I should be able to get the drawings and will upload them

31 minutes ago, Ridgeway Forge Studio said:

How is the interchangeable bit held in place? This could be a useful tool if it doesn’t put too much stress on a set screw or screw system. One punch fits all?

My one concern is that the threads on the aluminum inserts will get damaged as the threads themselves are also aluminum 

the center punch head and the hardened steel punch are going to be made out of an old hydraulic cylinder so I’m going to have to try and figure out what the best heat treatment is going to be for this steel 

The aluminum does sound like a worry, unless there is a shoulder or flush fit to transfer energy through the body instead of the screw.

if it’s for metalworking, I would consider a whole slew of reposee or chasing punches that could be good. 
If for hot work, I would think things that wouldn’t get too hot. The thermal expansion of either material may do damage over time to the construction.

Maybe i am confused here but why even put threads on them to begin with? A tight fitting round shaft with a flat for a set screw should be enough. 

A 1/4-28 thread would be stronger also depending on the drill you use you can get a stronger thread. You usually use a #3 drill for a 1/4-28 tap, they will get about a 60% thread. I can not remember the size but a bit smaller drill and it will give you a 70% thread. I have to go into work tomorrow and i will take a look at the giant chart we have on the wall telling me which drills to use with what taps. 

The reason I put threads on them is because at first I had planned to just make this myself using what I had and for the 1/4 20 over 1/4 28 that was also because of what I had available but if I was to redo this I probably would just use a flat for a set screw 

Here she is the body of one completed I haven’t put the set screw in but I don’t think I will need to 

On 3/19/2026 at 10:57 AM, Ridgeway Forge Studio said:

through

 

On 3/20/2026 at 4:11 AM, BillyBones said:

A

Ah I forgot gotta tag y’all 

Now i see it it makes more sense to me. 

I would suggest that you put 2 flats on the inserts so if they get jammed in place you can easily put a wrench on them to turn them out. Or tighten the tool down with. And maybe a wave washer between the 2.