Help needed with stiff Pratt Burnerd 3 jaw chuck.

[peak4Participant @peak4]

Posted by Macolm on 27/11/2022 17:00:08:

On checking, the Camlock taper is in fact 1 in 8 on the radius, so 1 in 4 on the diameter.

It occurs to me that, provided the gap when the cams are correctly done up is indeed only 2 thou (0.05mm), then only a bit more than half at thou would need to be removed from the taper diameter. I think this would be within the scope of lapping, and suggest a tool roughly as below to carry probably wet and dry paper, which is thin and uniform. This would need to be cut as an arc so as to fit the conical surface. It could be retained in place with pegs in slotted holes as shown.

This would sidestep the near impossibility (except in a tool room) to get the taper true enough to the precision necessary for grinding. It would not maintain the exactness of the original machining of the taper, but this could only be wrong by less than the amount removed. The taper provides a location, the faces in contact ensure the axis is correct.

Just re-reading my earlier post and it looks like a few words fell off whilst I was editing it.
I mentioned "Micrometer" blue and a bearing scraper, but didn't make it clear that I gently scraped the inner taper of the chuck(s) to suit the lathe spindle on my D1-4 GH1330.
It worked fine, I opened the taper out a touch and that allowed the flat faces to contact each other.

Bill

[Jonathan RichardsParticipant @jonathanrichards78237]

Thanks to all for the continuing input and advice. This is just a holding update because I haven’t had chance to progress matters as I had planned.

I have, however, established that a ‘shim’ cut from ordinary typing paper reduces the run out to 4 thou at 4 inches from the chuck, which is very much better than previously.

I need to try Hopper’s jaws/taper concentricity test next. Unless that throws up a major anomaly, perhaps unlikely given the paper shim result, I am going to try easing the taper slightly as suggested.

I don’t think I’m adept enough with a bearing scraper to risk that approach so I’m going to see if I can make a lap, as Macolm advises. I’ve never yet cut a taper on the lathe [at least not intentionally] so that should be a good learning exercise.

I’ll post again once I have some progress to report.

JR

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