Making custom Knockout Punches

Machine Shop
#1

OK, I have several holes I need to punch in some 18-14 gauge stainless. I’ve looked at the greenlee punches, and they work GREAT, but they are not the right sizes. I’ve done the step drill thing and while it’s OK for one hole, it’s a disaster for multiple holes.

The punches seem to be relatively easy pieces, so my question is whether it’s something that could be made relatively easily on the Colchester here.

Has anyone made something like this on our Colchester, and if so, what kind of steel did you have to use… the Greenlee punch I have seems to be of a stainless as well, but a low grade of it as it’s got some corrosion on it.

The two sizes of holes I need are 0.85" and 1.55" and maybe more depending on another set of fittings I have at home.

Anyone think this is doable?

#2

I definitely think it is doable. But it will not be easy. Hitting the right tolerance and dimensions on the pin and on the hole will be critical.

I would machine the steel for the parts in a soft annealed state. Then heat treat the parts once you have your desired geometry. The “Book of Truth” aka “Machinery’s Handbook” has a section on punch design.

1 Like
#3

We do have a punch. I don’t remember all the sizes we have. That also depends on if you can put the metal in the punch or not. Do you know what your tolerance is going to be? Standard 1/2 knockout will put a 7/8 hole or there abouts. I talked to @billyepps about making dies before, I seem to remember him saying that you needed approximately 1/2 the thickness of the material being punched for tolerance between your dies. I could be wrong, hopefully he can chime in.