How was this monkey wrench made?

The channel was broached.

Cheers Trevor Jones

Broach.

Tom

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

-- Ed Huntress

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.

Best wishes,

Chris

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

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

I think I found one:

Chris

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

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

Thanks, Ed. I've now got the explanation I wanted.

Best wishes,

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

It says "10 inch M.W." on it.

Chris

That sounds awesome if you need to cut internal gear teeth of a particular size. I'd certainly love to see a machine like that in action!

Best wishes,

Chris

Stick ta ya guns, Chris. or go here:

Of course ya owe me a pint now. :-)

Tom

Fine - it has the pipe wrench design but flats. The monkey wrenches I am used to had pipe jaws. These might be a variant that tried to take Crescent on. I think I have a variant in another direction.

Martin

Mart> Mart>> That isn't a monkey wrench. It is the tool before a Crescent.

Another thing I've been wondering about: is the broach inserted into an oversize hole and firmly held by guide rails, or is the broach self-centring in a tight pilot hole? In other words, what determines the precise location of the broached hole?

Best wishes,

Chris

Push broaches are usually located with their own guides, but they can be free-floating in jobs for which precise location is not important. In the case of a an old wrench, it could be free-floating. The punched hole was close enough.

The hole is undersize, not oversize. The leading end of the broach is undersize, and then the teeth progressively cut the hole to size.

-- Ed Huntress

Thanks. It's interesting to know that you can get both kinds. Looking at the wrench, the hole appears to be quite precisely located, so I imagine there was some kind of guide.

I meant oversize relative to the small end of the broach, not the finished hole.

Best wishes,

Chris