Collets – worth getting A grade (high/ultra) precision?

[mrbuilderParticipant @mrbuilder]

Looking at purchasing a set of ER collets either ER25 or ER32.

Has anyone purchased collets with TIR – 0.01mm vs the standard 0.02mm? And any benefit in doing so for model engineering / home workshop?

[mrbuilderParticipant @mrbuilder]

[John HinkleyParticipant @johnhinkley26699]

I have ER collets in both 25 and 32 series and I went for the "standard', i.e. lower tolerance. I believe that, for the margins to which a lot of us work, these are perfectly adequate. I don't possess measuring equipment that could differentiate between those sort of tolerances, anyway, even if my eyesight was good enough to read them!

John

[JasonBModerator @jasonb]

Really depends what accuracy you feel the need to work to. Also what will you be holding the collets in? will that have the better accuracy as not that much point in putting high spec collets into a holder or mill spindle that has lots of runout already.

I've not found the need for anything special, this is my X3 mill with a far eastern ER32 holder not sure if that came from Chronos or ARC, bearing nut from ARC and standard collet also From ARC. ). All those different far eastern parts would have a massive cumulative run out if what some say is true but the needle shows 0004" TIR or 0.01mm in metric.

[jimmy bParticipant @jimmyb]

I always run a DTI on anything I want running really true. Unless you are running high end equipment, I'd say high accuracy collets could be a waste.

On the other hand, the £25 for a set off Ebay, are probably, at best not great! I speak from experience, I have a few good sets from "well known suppliers", a drunken purchase off Ebay resulted in a set that have, high runout, missing slots, huge burrs and highly optimistic sizing..you pays your money and makers yer choice!

Jim

[SillyOldDufferModerator @sillyoldduffer]

I agree with Jason, with a slightly different spin.

If you are chasing accuracy you have to consider the whole system, not just one part of it. High-end collets won't fix a mill that's out of tram. No amount of expensive accessories will fix a worn-out machine that got bent when it was scrapped by a previous owner.

Make a list of everything that could be messing up the machine's accuracy. Then establish by measurement which item is causing the largest error and fix it. Remeasure the whole system and repeat as necessary. If doing that takes you direct to collets, hurrah! If fixing something else restores accuracy, you've saved a bob or two and not wasted your time.

There's another approach. If you're reasonably happy your machine is accurate already, no problem 'improving' it by picking up 'better' accessories. Ideally at bargain prices. If you enjoy owning 'quality' tools, why not? But be aware that any improvement achieved by random purchasing or guessing is down to luck, not judgement.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 28/10/2017 08:49:51:

If you are chasing accuracy you have to consider the whole system, not just one part of it. High-end collets won't fix a mill that's out of tram. No amount of expensive accessories will fix a worn-out machine that got bent when it was scrapped by a previous owner.

.

Wise words, Dave … but I would like to expand upon them a little:

Tolerance build-up is, of course, a statistical beast … so we're never quite sure whether errors will add or subtract.

I find it best to think in terms of 'confidence level'

If we have two components that are each [say] within spec to a confidence level of 90% then when we combine them, the confidence level falls to 81%

MichaelG.

[nigel jones 5Participant @nigeljones5]

I bought a cheap set from china and they are brilliant! Now use them in lathe and mill.

[Anonymous]

How important the TIR is depends on the size of the cutter. A runout of 0.02mm isn't overly important on a 12mm cutter running at a tooth load of 0.1mm/tooth or more. But for a 1mm cutter running at a tooth load of less than 0.01mm/tooth it's rather critical. Of course if the rest of the spindle/toolholder doesn't have a better TIR there is no point in buying precision collets.

Andrew

[RobinParticipant @robin]

I just bought a set of 13 ER11's and once I saw 0.008mm advertised ​I just had to have them. There was a suggestion they cut them out of silver steel rather than boring old HC but I would never know. I am a total sucker, I used to fight it but now I give in to temptation and I have to admit it feels all warm and glowy

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