"Christopher Tidy" wrote in message
...
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?

How did they make the hole into which the broach was inserted? With a
twist drill?

Best wishes,

Chris

Here are some photos and descriptions. Google "pull broach" and you'll get
more than you ever wanted to know:

http://www.ohiobroach.com/index/broaching2

http://www.americanbroach.com/tools.htm

http://www.kingsfordbroach.com/products.htm

http://www.millerbroach.com/engineering.html

http://cgi.ebay.com/STRAIGHT-SPLINE-...QQcmdZViewItem

Pull broaches are a lot longer, but you can search "push broach" to round
out the picture. Your wrench likely was push-broached.

The holes in forgings like that are usually pierced with a piercing punch
while the metal is red hot. That was the "second hit" I was talking about.
This is a carryover from the days of blacksmithing. Hot-piercing is a common
process in forging all sorts of products, whether by hand or by machine.

--
Ed Huntress