Modifying collets?

This topic has 6 replies, 4 voices, and was last updated 25 April 2017 at 10:30 by Martin Connelly.

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24 April 2017 at 14:31 #294751
Andrew Tinsley
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@andrewtinsley63637
I have an almost complete set of Imperial Hardinge collets and quite a few duplicates. If Sod's law dictates that I need one of the "missing" collets. Is it possible to "bore" out one of the smaller duplicates and manufacture the "missing" size?

If so, how would one go about doing this operation? I assume that the Hardinge collets would be quite hard, does this mean some form of grinding? or could one bore and ream? Quite what the edges of the splits would do to reamer, I hate to think!

OK, this is a hypothetical question, which hasn't arisen yet, but I am interested to see if the job is doable. Usually I never have the size I want of anything!

Andrew.

Edited By Andrew Tinsley on 24/04/2017 14:32:04
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24 April 2017 at 14:31 #8677
Andrew Tinsley
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@andrewtinsley63637
24 April 2017 at 16:42 #294760
Martin Connelly
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@martinconnelly55370
The way soft emergency collets are made to size is to have spacers in the gaps, put the collet in its holder (spindle position for example) and tighten it up. It is then bored to the required size. To do it with a hardened collet you would have to grind it instead of boring it. If you look at pictures of emergency or soft collets you can usually see the spacers in place. After sizing remove the spacers.

Martin C
24 April 2017 at 21:05 #294790
Andrew Tinsley
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@andrewtinsley63637
Thanks Martin,

I think this must be my 3rd reply to you. The others have disappeared in cyberspace! Your reply makes it all clear!

Just one query, what would you use to grind the very small sizes of collets, say 1/16", some sort of diamond burr?

Thanks,

Andrew.
24 April 2017 at 21:37 #294798
Michael Gilligan
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@michaelgilligan61133
Andrew,

I hope you don't mind me joining the discussion:

Martin's advice is exemplary … but, if you are considering small sizes, I think it may be preferable to make [or even buy] 'slave collets' to fit inside one of the larger Hardinge ones.

MichaelG.

.

P.S. … Here is a cheap & cheerful ebay version: **LINK**

http://www.ebay.co.uk/itm/171660959519

… but if you're making your own [maybe in brass] you might start with oversize rod; finishing the bore first, and then skimming the OD to achieve better concenricity.
25 April 2017 at 01:13 #294823
Enough!
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@enough
Posted by Martin Connelly on 24/04/2017 16:42:34:

To do it with a hardened collet you would have to grind it instead of boring it.

I've actually modified ER collets (on the face, not the bore) by just using regular carbide-insert tools.
25 April 2017 at 10:30 #294849
Martin Connelly
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@martinconnelly55370
MG's advice regarding slave collets seems like a good idea. If you are missing a few sizes and are going to use that size regularly buying something like that makes sense.

If you are only after occasional use then a soft/emergency collet may be the way to go. These have a number of advantages because if you make one 1/16" for example then if it gets worn make it into a larger size and make a new 1/16" one. Also you can use them like soft jaws on a chuck and machine them with a pocket. For example if you had a lot of washers to drill out to a larger hole size then a soft collet would make mounting and drilling them an easy task. Note a steel soft collet is only relatively soft compared to a hardened and tempered collet and can last quite a long time before wear starts to be a problem.

If slave collets are hard to find you could consider an ER16 (or other size) collet holder with a parallel shank to fit into a collet or 4 jaw chuck on your lathe.

Grinding a collet to 1/16" sounds like a problem, I would think annealing and drilling may be the best solution then you have the equivalent of a soft collet. EDM would also work if you had access to a suitable machine.

Martin C
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