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A workholding question

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Robin Graham16/07/2018 22:45:36
455 forum posts
92 photos

A while back I asked for advice about bearings for rollets I make for a ceramicist friend. Amongst the many helpful suggestions I received was the idea of using a cone and socket, and I have at last got round to experimenting with that idea:

rolletwithholder.jpg

 

rolletparts.jpg

 

This is a lash-up for testing, I can do neater than that!

My question is about turning the bush with the cones - the first cone was simple enough because the parent stock was in the chuck, but then i had to part off and turn the second with only 6mm length of round to grip in the chuck. I may have got away with it - the wheel seems to run true, but I can't help thinking there must be a better way. I haven't yet got a collet chuck for the lathe which I guess might be an answer.

Any thoughts?

Robin

 

 

 

Edited By Robin Graham on 16/07/2018 22:47:20

Roderick Jenkins16/07/2018 23:10:13
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1634 forum posts
412 photos

Robin,

I'd make a split collet that can be held in a 3 jaw chuck. Most 3 jaw chucks have good repeatability so if the collet is machined in the chuck and the orientation of the collet with respect to a particular jaw is noted and the same socket is used to tighten the chuck then there is a good chance of being able to turn the job around with acceptable concentricity.

HTH,

Rod

Robert Dodds17/07/2018 00:05:11
253 forum posts
28 photos

You could make life easier if you had a through hole in the bush, with countersink if required (c/sink tool will follow the hole on the second side and then machine the cones on the two pivot screws. They don't rotate in use so it all runs true

Regards Bob D

not done it yet17/07/2018 08:06:09
2379 forum posts
11 photos

Get a suitable ER collet set. End of concentricity problems - unless a cheap china import, which might be risky.

Mick B117/07/2018 09:02:41
799 forum posts
47 photos
Posted by Roderick Jenkins on 16/07/2018 23:10:13:

Robin,

I'd make a split collet that can be held in a 3 jaw chuck. Most 3 jaw chucks have good repeatability so if the collet is machined in the chuck and the orientation of the collet with respect to a particular jaw is noted and the same socket is used to tighten the chuck then there is a good chance of being able to turn the job around with acceptable concentricity.

HTH,

Rod

+1 for that.

If the chuck's worn, a set of soft jaws bored to suit is a working alternative.

Hopper17/07/2018 09:49:41
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3023 forum posts
50 photos

+2 on Rod's suggestion of the bespoke collet marked to match the chuck jaws for repeatability. "A split collet" consisting of any noggin end from the scrap box drilled to the size and split lengthways on one side with a hacksaw. I suppose you could bore the hole to finish size if you were of a fussier nature than myself.

KEITH BEAUMONT17/07/2018 09:57:51
45 forum posts
12 photos

Robin

,Machine cone as before,part off at half length. Repeat for second half. Super glue the two halfs together.

Keith

Brian Wood17/07/2018 10:09:15
1745 forum posts
35 photos

I have to agree with Robert Dodds, make the screws pointed instead, so much easier.

Brian

Robin Graham21/07/2018 23:00:08
455 forum posts
92 photos

Thanks for all your suggestions - Roderick's split collet method worked perfectly well. I was surprised by the accuracy / repeatability I got with such a simple thing. I've also tried doing it the other way round (points on screws) as Robert suggested - it is indeed easier that way! So the upshot is that the end user has a kit of bits which he can swop in and out and see what works best in practice. Whatever, I have learned a new technique.

I tried using the 2MT ER 25 collet chuck from my mill in the lathe, but the lathe has a 5MT spindle, so I had to go 5/3/2 using the sleeves I have - unsurprisingly perhaps the runout at the work was greater than using the 3-jaw which came with the (Chinese) lathe.

Thanks again, Robin.

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