"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.

--
Ed Huntress