Sharp internal corners

[peter@slater]

True, true. That's why I recommend testing it out by pushing it thru once if the materials is soft enough. You wouldn't drop a wad like that and then find out it didn't work for you. It does save folks alot of time though. If the material is too hard, pushing it through will chip the corner of the broach, also a bummer.

[miljnor]

just noticed your name too.

They are very good tools I have three holders myself. Just didn't want the guy thinking "Wow 50-100, what a deal" and then come away pissed off.

[WhiteTiger]

Swaging seems to have been overlooked. It would be rather easy in aluminum. Punch the round hole, but leave a raised boss on both sides, then use a formed punch and die to displace one side of each of the raised ridges and form the flat in the hole.

I've done something similar working with 4140 steel in making rifle bolts; works fine if you make the tooling correctly.


Tiger

[miljnor]

I can almost imagin that!

How about a picture so I can understand?

[WhiteTiger]

This is the simplest form. Go ahead and make the round hole, but leave the raised ridge of material around it. Put the flat sided mandrel in place, put the blank on a backer and with a flat sided punch and a bfh drive the material of the raised ridge down into the hole and let the mandrel govern the form.

I'd literally do it with a punch and hammer for just a few pieces, but for production quantities I'd make up a small die set and do the swaging with an arbor press. Needless to say the remainder of the raised ridges are machined away afterward

EDIT- for thin sections it's ok to work from one side only, but if the hole is more than 1 diameter deep, it's best to leave a ridge on both sides and swage from both directions at once. Done right this can be stronger than a form broached hole, thanks to grain flow of the material.

[miljnor]

Now would you want to capture the raised area to keep it from forming outward as well as inward

[WhiteTiger]

For production quantities yes, I'd use a capture ring as part of the die on each side. Needn't be a deep ring, just enough to guide... say about 10-15% of the height of the raised boss. Shape and angle of the working punch face should be enough to control though.

For just a few pieces, I'd just count on my control of the punch and hammer to govern material flow.


Tiger