"Christopher Tidy" wrote in message
...
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

Yeah, that's it. I've seen them as big around as your thigh, and nearly 20
feet long. That one machined the internal teeth on the ring of a planetary
gearset in one pull -- maybe five to ten seconds.

--
Ed Huntress