Subject: broach?

From: [email-masked] (Jim Purtilo)
Date: 29 Aug 1993 14:25:40 GMT

What is "broaching" in metalworking, really?  What is a broach bar? (Other
than a bar for performing broaching ....)

Thanks

Jim

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From: [email-masked] (Jim Purtilo)
Date: 29 Aug 1993 21:53:49 GMT

In article <[email-masked]> [email-masked] (Jim Purtilo) writes:
>  What is a broach bar?

And to head off mail from the *rest* of you wise guys, I'm sure the answer
is not "A place where you go to pick up broaches .... "

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From: [email-masked] (gary preckshot)
Date: 30 Aug 1993 20:34:06 GMT

In article <[email-masked]>, [email-masked] (Jim
> is not "A place where you go to pick up broaches .... " 

A broach is a hardened steel widget that is either pulled or pushed through
a hole to cut internal shapes such as keyways or splines.  Broaches are
also used to cut external shapes, which generalizes the description to a
one-pass cutting tool or something.  They look like a very aggressive rasp
or a tool steel cob, and you can imagine their action as very similar to a
rough cob being dragged through an orifice.  A shape the size and form of
the largest cross section is left behind.

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From: [email-masked] (John Kopf, X6305)
Date: 1 Sep 93 19:26:40 GMT

> than a bar for performing broaching ....)

"Broaching" is to enlarge a (through) hole by FORCING a cutter ("broach bar")
through the existing hole.

For example, you have a round hole and you want it square.  Take a square bar
of the final dimensions, turn down one end to fit into the existing hole, and
machine a *long* taper, graduating from the round hole to the square section.
now, make some "teeth" on the edges (it's starting to look like a tapered tap,
except for the absence of the "flutes").  Now harden this, and FORCE it through
the round hole -- each tooth will take off another shaving, slowly converting
the hole from round to square.  needless to say, this takes a LOT of pressure
(no, you DON'T want to drive it through with a hammer!)

The same technique can be used for forming keyways, hex holes (for allen 
wrenches), etc.  I don't know if it can be used for blind hole;  I suspect not.

Hope this helps.

JK

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From: [email-masked]
Date: 2 Sep 93 12:02:10 PST

>> than a bar for performing broaching ....)

...Good description of broaching deleted...

> I don't know if it can be used for blind hole;  I suspect not.

Not being an expert on the subject, I just thought that I would try to answer
this question based upon observation.

I suspect that broaching CAN be done on a blind hole, as I have seen a great
number of hex drive objects that have blind hex holes.  When examined closely
at the bottom, one can see the shavings bent into the center, and pounded
down flat.  I can only assume that some sort of broaching technique was used 
to create the hex drive holes.

			John.