Christopher Tidy wrote:
Ed Huntress wrote:

"Christopher Tidy" wrote in message
...

Ed Huntress wrote:

snip

The channel was broached.



Probably after being hot-punched in a secondary forging operation.
The whole body could be forged and punched in two hits.


Thanks for the thoughts. That was my own best guess.

I'm a little surprised that it's possible to broach a deep channel
with such thin walls (only about 3/32" thick) without everything
getting mangled. Guess the key must be getting it hot enough.



Production broaching is not much like the kind we do in hobby work.
The broach itself looks more like a long, extremely coarse tapered
file -- some as long as twenty feet or so -- with each successive
tooth cutting a thousanth or three more than the last one, typically
cutting on all sides at once (or not, depending on the job -- some cut
on only one side at a time). They come in two general types:
pull-broaches and push-broaches. They were made from a single piece of
tool steel but recent ones have replaceable inserts.

The broaching likely was done cold. The rough-punched body would be
held and supported in a fixture. Designing a feature for support is an
important part of designing the forging.


Thanks, Ed. That's interesting. Does anyone have a picture of one of
those broaches?

I think I found one:
http://www.ohiobroach.com/index/broaching2

Chris