5C collets

[Mike BondarczukParticipant @mikebondarczuk27171]

Hi all,

I have been using ER32 collets for some time now and know that there is a 1mm tolerance on diameter of parts to be held, at least on the metric versions.

I am now switching over to 5C collets as part of a new lathe set-up but cannot find any reference to the allowable holding range for the 5C system in any of the flavours, i.e. metric, imperial, square and hex.

Can anyone point me in the direction of finding the ranges please.

Mike

[Mike BondarczukParticipant @mikebondarczuk27171]

[Michael GilliganParticipant @michaelgilligan61133]

Mike,

I believe that Hardinge published some useful details [I will post the link later, if I can find it]

Basically, however, all the 'Watchmaker style' collets are strictly 'single size'. … There may be a [very small] proportional relaxation in tolerance with increasing size, but: In the sizes used in a Watchmaker's Lathe, the number on the collet expresses its bore in tenths of a millimetre, and good practice is to only hold diameters within +/- one quarter of one size increment … Yes, this means that material is skimmed to an acceptable size if needs be.

The 'problem' is that the collets are only slit from one end … sketch the geometry of clamping oversize/undersize material, and you will see the inevitable.

MichaelG.

.

Found it [easier than I expected] … Hardinge

Edited By Michael Gilligan on 17/01/2016 11:36:19

[John HaineParticipant @johnhaine32865]

As Michael implies, essentially zero (though you might get away with holding items slightly smaller than nominal). My experience with Myford pattern MT2 collets is that you essentially have to use them on nominal sizes only – I have a limited set of ER40 collets as well for the in-betweens. If you're happy with ER32 I'd stick with it.

[John Stevenson 1Participant @johnstevenson1]

In practice which often differs from theory, something like plus two thou to minus 10 but the more you get undersize the more rock there is.

There is no collet system that will please all but the ER's are fast becoming a good gap filler in both work holding and tool holding and there are bridges to accept both like this 5C to ER from ARC.

050-070-00800 5C to ER32 Collet Adaptor

One often quoted advantage of 5C over ER's is you can get square and hex collets in certain sizes, but as long as you are not ripping 10mm off at a time Jason has prooved that ER's will also hold square and hex of any size that fits in the range.

[JasonBModerator @jasonb]

A few thou under seems to be OK for me and lets face it if it wasn't you would only be able to machine PGMS and Silversteel.

I have one of the adaptors that John shows which works well and allows me to fill in the gaps in my Metric 5Cs with ER32 collets or when the 1/32" increment imperial 5Cs won't fit the work.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 17/01/2016 13:18:37:

A few thou under seems to be OK for me and lets face it if it wasn't you would only be able to machine PGMS and Silversteel.

.

[or pre-machine to a suitable diameter and finish]

… At which point, I think we're all in agreement, aren't we ?

… just expressing ourselves differently.

MichaelG.

[mark costello 1Participant @markcostello1]

I was always told +or- .005 from size, but .005 is hard to get in some of them.

[Mike BondarczukParticipant @mikebondarczuk27171]

Gentlemen,

A perfect series of responses which now clarify the tolerances for 5C collets, or rather the lack of them compared to the ER series.

I like the idea of the 5C to ER32 adapter and may go that route to keep things simple and flexible.

Many thanks for all of your responses,

Mike

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