Tool and Die making 101
So @Chainmaildave has proposed a fairly tricky first project that he wants to build for his intro to machining session.
He really wants a punch and die set to make scales like these:
We’ve been spit-balling possible ways to make that happen, and think we might have a workable way to do it.
We’d need to make two parts… a punch:
And a die:
As well as some miscellaneous tooling to make them and some jigs to use them with a small arbor press etc.
The clearance angles have been greatly exaggerated to make them clear in the drawings, I’m thinking 0.5-1 degree on the die, and we’ll just ever so slightly dish the punch on the grinder. We’re not set up to Blanchard grind or do other fancy things… Dave has some steel he wants to try it with. We may try to case-harden the stuff.
The hole in the die needs to be slightly (several thou probably) bigger than the punch for it to cut properly. It is dependent on the material to punch and the thickness of the material. So I’ll need @Chainmaildave to decide what size scales he wants to make, what material and thickness.
I plan to use the unipunch page to do the calculations:
Does the bottom of the die have to be cupped? I am so a fly-on-the-wall for this one…
It’ll cut with much less press force if the punch is cupped.
The die needs about 0.5-1 degree of relief so that the metal can spring back as it punches through. Otherwise it’ll bind as you punch out the pieces.
I have a plan for how to make the die in two parts.
Order of operations to make the punch.
- Mount the bar of steel in the 4-jaw chuck, turn and face one end to have true reference surfaces.
- Offset the bar, and drill a hole for the hole in the scale.
- Rotate the bar in the 4-jaw by 90 degrees, and adjust the offset to let us turn down the half-leaf section.
- Rotate the bar in the 4-jaw by 180 degrees and turn down the other half-leaf section.
- Either use shallow taper-facing, or hand-grinding to slightly dish the cutting face.
Harden, temper, maybe case-harden the steel. Stone the edge to bring it up to sharp.
Order of operations for making the die:
- Bolt two pieces of hardenable steel to a fixture spaced so that a boring bar on the lathe can cut a suitable tapered hole, or a boring head on the mill with a modified tool can cut it. We’ll figure out a way.
- Bore the hole.
Remove the plates from the fixture.
Harden and temper the plates, stone the face to get cutting surfaces.
Bolt them both to a plate that will hold them in a leaf shape, and support the cut.
Maybe add a pin to punch the hole, add a stripper plate, guides to feed strips of sheet stock properly aligned etc.
Mount it in a press, and get to work. If we fixture it like a unipunch, we could use a trip-hammer to make about 3 scales per second. Maybe ten times that if we can also add a power feed.
I have a bunch of tapered end mills at the shop. If you figure out what angle you need I’ll be happy to donate one to this project.
Thanks @BrianB … I was planning on either doing the taper in the setup (deliberately introducing a taper is useful for understanding how to make flat and true parts) or by custom grinding a cutter to bore the hole like a form tool on a lathe… Single point boring the small dimension of the cut then plunging the tapered cutter slowly to cut on its full face… Ideally I’d figure out how to adjust the radius of the boring head in a precise manner while the mill is running… The more I describe this the more I think it’d be easier and safer with the plates bolted to the faceplate of the lathe and bore the hole there…
This article has a very nice breakdown of the punching operation and the features found on good tooling…