Reworking a Hardinge MA99E collet?

[Andrew TinsleyParticipant @andrewtinsley63637]

I am missing a couple of sizes of Hardinge collets, that I would like to have. Not wanting to wait forever, for Ebay to produce them. I thought that maybe I could rework a couple of duplicate collets that I have.

So, simple mind says, put collet into Myford collet chuck, drill out just undersize to diameter required and then ream the hole to size. So what can go wrong? I suppose the steel could be hardened and hence difficult to drill and ream. Maybe the reamed hole could be a bit oversize and then it would not hold the specified diameter?

Is the idea practical or are there any other things that could mean it is a non starter?

Thanks,

Andrew.

Edited By Andrew Tinsley on 09/02/2017 16:27:34

[Andrew TinsleyParticipant @andrewtinsley63637]

[JasonBModerator @jasonb]

Probably need to put packing in the slots much like you see on emergency collets so it won't close down while being worked.

Better to bore it out which also gives the option of carbide tips incase the collet is hardened.

[Andrew TinsleyParticipant @andrewtinsley63637]

Thanks Jason,

I understand the comment of using a boring tool instead of drilling and reaming, that makes sense! I know nothing about emergency collets, so I am unaware about packing the slots. Being simple minded on these matters, if you pack the slots and then bore to size, will this give the correct diameter, when used in anger with a rod of the nominal bored size? I can't quite get my head round the problem.

How much packing would be required and would the end results vary with the amount of packing used? I assume that the slots must be closed as viewed from the collet front face, before boring takes place? I am afraid I have a mental blackout when trying to figure this out!

Thank you,

Andrew.

Edited By Andrew Tinsley on 09/02/2017 17:43:54

[JasonBModerator @jasonb]

If you were to put the empty collet into your holder and tighten it up enough to stop it turning while boring then the collet will tend to close down. IF you then bore it like that you will get a straight bore but when undone from the holder it will spring back open and you will have a bell mouthed opening.

The emergency collets come with pin as the packer but it just needs something the width of the slot, I would measure with feeler gauges and then mill a bit of scrap aluminium to thickness then cut small bits to place in the slots at the outer end of the collet.(both ends for collets that close at bothe ends) You are aiming to stop the collet closing down but at the same time don't want to force it open.

A similar method is used when machining soft chuck jaws or regrinding old chuck jaws where a spacing ring allows you to close teh jaws up tight but at the same time holding them open.

These are 5C emergency collets with the spacing pins in place.

[Andrew TinsleyParticipant @andrewtinsley63637]

Thanks Jason,

That makes a little more sense to me. Using the Myford collet chuck, if you screw the nose down, then the outer rim of the collet is snug against the nose. At this point, is the bore that stated on the collet? This is before you start to close down the collet. I suppose I really ought to go and measure this dimension, rather than asking here on the forum. Not so easy with the smaller bore collets that I want to modify. The only way I can think of is turning down a rod until it "just" fits.

Andrew.

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