Correcting an Incorrectly Broached Keyway

Key for a template, spotting blue for final finishing if absolute precision is necessary, single bevel cape chisel and a 1 lb ball pein hammer.

How else would you do it?

:-)

Mark Rand RTFM

I assume the actual keyway in the shaft is parallel sided and so is the keyway in the flywheel. However the key tapers "radially" and therefor the "top" of the keyway in the flywheel tapers from outside to inside. outside dimension being the greater. or am I wrong?

Need to know before I apply the grey matter.

Richard

Yes, something along those lines.

I'm trying to find the drawing of the flywheel so I can check the actual taper.

The keys are about 6" long with gib heads.

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk

Ok here is my two pennorth Turn up a headed plug to match flyweel bore Machine a keyway into it (through the head as well) keyway parallel sides but with the required taper shallow at head end Make a broach from a piece of gauge plate with lead say .005 - .010" lower than teeth. Broach long enough to pass teeth through flywheel with push end still showing Drill and tap three holes in head for some adjuster screws. Fit tool to flywheel adjust screws so so broach lead just trapped, lubricate all. Belt broach through. slacken screws a tad push plug in pass broach through again, and again and again.

Just what Mark said but a bit of finesse

This information is worth exactly what you paid for it.

BTW how wide is the key?

Richard

Whenever I see one of these on an old engine, I am always curious to know how one is supposed to remove them after they have been in place for many years. The only kind of puller I can imagine would be something like a thick notched washer with three jacking bolts, but I have a suspicion that it might break the head off the key rather than remove it!

Alan Bain

Crow bar :-)

Mark Rand RTFM

There is a device with a tapered head that you can use, but for keys that are well in place, sometimes to have to resort to other means :-))

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk

The usual tool is a key drift. A slow tapered wedge with the working face also tapered a few degrees so as to bite into the corner twixt head and key. Clogged smartly it will usually work. Superior "cow-heel" versions are also curved to allow use on dished flywheels whose rim is wider than their bore. Various versions of what you imagine are also used but as they cannot impart any impulse they do, as you surmise, often rip the head off. Heating the key with a small tip on the Oxy/fuel-gas, and allowing to cool fully, improves the chances dramatically.

hth

60 years ago we use to use a wedge and a hammer (heavy) but things have probably changed a lot since then.

I expect that the technique of applying constant pressure with the key drift and then lots and lots of small blows to the hub would eventually do it too.

When I've tried to extract taper keys, it has made a mess of them. Instead I've had more success using a very strong puller to pull the wheel off with the key in place. I put a piece of steel behind the head of the key to stop it sliding further in. I haven't tried this method on anything larger than a 1 1/4" diameter shaft, and I'd be cautious using it on wheels that look fragile, but so far it's worked very well.

Chris

Surely anyone with a slotter should be able to set this up and machine it correctly though a shaper may have more difficulty. The taper is about 6 degrees. The biggest problem may be setting up the casting. If the flywheel outer faces are machined tru to the bore, that should be easy enough.

John

A second thought just after I posted would be to machine a dummy shaft with a taper keyway then use a parallel broach. As for removing taper gib heads, good luck. They can lock in very tightly. If a wedge or puller is used between the flywheel and ket head then heat is applied to the flywheel, either the key comes out, the flywheel moves on the shaft or you try someting else. I've resorted to drilling and tapping them for a pullet bolt. After that, I've had to drill them out or even gas axe them out. That normally means a new keyway is needed in both components although occasionally you can be lucky when the heat does it's job of loosening things.

John

Many thanks for the thoughts, John.

The keys are out and not a problem, it's just the issue of the parallel keyway.

The drawing for the flywheel is the cause of the issue, it states '2.832" at Deep End', but gives no dimension for the other end or any taper on the keyway itself. Presumably as this was all done in-house there was no 'need' to tell anyone what the taper was as they all knew it.

The other thought has been to leave it parallel and make up a close-fitting key and Loctite it in place.

Peter

-- Peter A Forbes Prepair Ltd, Rushden, UK snipped-for-privacy@prepair.co.uk

When I dealt with keyed sprockets and pulleys we grub screwed the boss onto the top of the key. That locked the sprocket and didn't bruise the shaft. It makes removal easier too.

John