Excentric collet

[Raymond AndersonParticipant @raymondanderson34407]

Hi Nigel, Yes, I suspect that is the reason they are offered in a "Restricted " range of closure, to ensure that the TIR remains as close to the Nominal size TIR . All will be answered once I hear back from the various makers I have contacted.

[Raymond AndersonParticipant @raymondanderson34407]

Hi Michael G, until I hear back from the makers I have contacted, there is an interesting piece of info from http://www.centaurtools.com Look for the RD/ER Collet info [the green zone and the red zone.] its about halfway down the page. Interesting.

Cheers

[Michael GilliganParticipant @michaelgilligan61133]

Thanks, Raymond

That makes a great deal of sense.

I look forward to seeing the response from Regofix.

Keep up the good work, Sir

… we'll get to grips with this eventually [ouch!]

MichaelG.

[Raymond AndersonParticipant @raymondanderson34407]

Michael,This has certainly held my attention [ouch, ouch]

[Raymond AndersonParticipant @raymondanderson34407]

Just heard back from Regofix, and the quoted TIR is across the full range of each collet. only guaranteed if the whole system is Regofix. Collet holder, closer and Collet.

That would then explain why when I did some random tests on Saturday that the Regofix collet showed a slight [like the all the others tested ] increase in the TIR when closed down to its minimum Ø. none of the collets tested showed large increases of TIR they were only [at worst] an increase of iirc 7microns Still to hear back from the other makers.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Raymond Anderson on 25/04/2016 16:27:23:

Just heard back from Regofix, and the quoted TIR is across the full range of each collet. only guaranteed if the whole system is Regofix. Collet holder, closer and Collet.

.

Thanks, Raymond

That is as I hoped .. and the caveat is entirely reasonable.

Much appreciated.

MichaelG.

[Raymond AndersonParticipant @raymondanderson34407]

No probs Michael. I certainly learned something new during this discussion. I was of the opinion that the collets would show an increase in TIR when closed down, but not so with the Regofix, I still await the responses from the other makers.

cheers

[Raymond AndersonParticipant @raymondanderson34407]

Hi Folks, have just had the latest bunch of replys. Kennametal, Royal, and I even contacted Sandvik Coromant. and the consensus says that there will be a variation in runout over the entire range of each collet, but it should always be within the collet spec. which most standard accuracy ones are ≤ 10µ. Even the highest accuracy ones [Fahrion ] £££ are ≤ 3µ and they should also stay "in spec " [ with their chucks ]

So Yes, all "good " collets should close down across their entire range and still be within the specified TIR. This has certainly been interesting [for me anyway ]

[frank brownParticipant @frankbrown22225]

As these collets are closed by the inside face of the nut pushing the collet into the holder. The inside face of the nut would have a big effect, suppose it only touched the collet face on one side? Could be interesting putting a smear of grease on the collets face or even engineers blue.

In fact it's an interesting engineering challenge to machine, the inner surfaces of the closing nut concentric to the thread. Especially as they should be ground.

Frank

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Raymond Anderson on 26/04/2016 14:12:38:

… So Yes, all "good " collets should close down across their entire range and still be within the specified TIR. This has certainly been interesting [for me anyway ]

.

Thanks again, Raymond … You have obtained a proper 'benchmark'

The discussion will now surely progress to the usual:

• "fit for purpose vs fit for purse" and
• "look what I got away with"
• < etc. >

Nothing wrong with that … but at least it is reassuring to know what the ER system can do, if made and used as intended.

MichaelG.

[Raymond AndersonParticipant @raymondanderson34407]

Yes Michael, it certainly shows just how accurate the ER system is, especially when the better makes are used. [ which leads nicely into the fit for purpose / fit for purse domain]

Cheers.

[Anonymous]

Raymond: Thanks for pursuing this with the manufacturers. I'll have to change my view in light of the evidence. Although as a caveat I posit that the grip of an ER collet when closed down might be less than when used at its largest diameter. For holding work, which is presumably a relatively soft surface with some compliance, this isn't likely to be a problem. It may be more of an issue for carbide tooling in particular where the shank is finely finished and is very hard with no 'give'. In that case a closed down collet is essentially holding on a series of line contacts rather than a surface contact.

Discuss!

Andrew

[Raymond AndersonParticipant @raymondanderson34407]

Hi Andrew, I know where you are coming from as regard grip when closed down at the bottom of it's range. I don't know the answer to that one. Yes, when used for workholding I would expect them to have a very firm grip even when closed right down. Toolholding I would suspect that they would also have a very firm grip even on carbide shanks. although not as much as a Albrecht hydraulic chuck [which by the by are reckoned to be the worlds best milling chucks]. I could easily find out. Now,, [and this is only my opinion] I think it would still need a great deal of force to have a cutter slip in the collet especially if the collet closer was tightened to the specified torque. In fact iirc I should have a brochure from Albrecht comparing the grips of various milling chucks Hydraulic,. Shrink fit, collets [various] I will see if I can find it. If no joy, then I will try getting it again from Albrecht. or maybe online. Watch this space.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andrew Johnston on 26/04/2016 17:20:27:

…. In that case a closed down collet is essentially holding on a series of line contacts rather than a surface contact.

Discuss!

.

Quite so, Andrew … and the folk at Centaur Tools seem to be of like mind.

See Raymond's earlier post; to which I replied:

That makes a great deal of sense.

MichaelG.

[Neil WyattModerator @neilwyatt]

I'm surprised no-one has mentioned Richard Gordon's little tip for improving the runout of ER collets.

MEW 232 page 34.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 26/04/2016 19:56:00:

I'm surprised no-one has mentioned Richard Gordon's little tip for improving the runout of ER collets.

MEW 232 page 34.

Neil

.

We were waiting for you to to do the 'back-issue sales pitch', Neil

MichaelG.

[Raymond AndersonParticipant @raymondanderson34407]

Got some free time just now, so have fired of an e-mail to Regofix and Sandvik Coromant as regards the holding power of a collet when closed down to the lower end of it's range.

Will post the answer once it's received.

[Raymond AndersonParticipant @raymondanderson34407]

 

Mies Michael <mmies@rego-fix.ch>

To

E ANDERSON

Today at 10:59

Hi Raymond,

We recommend to each clamping diameter in an ER collet a certain tightening torque. It depends on nut type and also on diameter, you like to clamp.

The tightening torque is higher than the transferable torque.

**LINK**

You see that the recommend tightening torque for Ø 11.50 mm is the same as for Ø 12.00 mm. Finally the transferable torque is the same.

I hope that the answer helped.

Best regards,

Michael Mies

Area Sales Manager

REGO-FIX AG

Obermattweg 60 / 4456 Tenniken / Switzerland

P +41 61 976 1456 / mmies@rego-fix.ch

http://www.rego-fix.com

As Promised here is the info regarding the grip through the range of each collet. Although I have only posted 1 reply here, ALL manufacturers contacted agreed the the torque is reduced at the lower end of each collets capacity. By how much is governed by many things. ie Ø, tightening torque, quality of holder and collets.

High quality holders, collets, and closers suffer much less than low quality ones.

Finally, all makers I have contacted [Kennametal, Sandvik Coromant, Rohm, Regofix, Royal, Fahrion and Big Kaiser [I think thats them all ] have all taken the trouble to reply and explain things in detail often attaching some pdf's and that, from big high class firms, to a "hobby user " is great service . I was originally thinking nah,, none of these firm will reply welll how wrong I was. High class products and high class service.

[AjohnwParticipant @ajohnw51620]

Just an observation. I have yet to see a tolerance on the bore of an er collet and if there was where would we obtain the cutter that was an exact fit in it ?

John

–

[Raymond AndersonParticipant @raymondanderson34407]

Can't answer that, but for instance 16mmØ shank would never be dead nuts on 16mm It would be under [something like 15.997] never over. So me thinks a 16/15mm collet would be a few µ over the 16. or they may even be toleranced from the lower Ø. I have no idea on that. But later on I am going to insert a carbide bar that I had specially made,into a 20 Ø ER32 and see how much [if any] it expands the collet. The bar in question is 19.998 Ø

[Anonymous]

Raymond: Thanks for taking the time and trouble to get this information from the manufacturers. Most interesting, and I've certainly learnt a lot.

Andrew

[Raymond AndersonParticipant @raymondanderson34407]

Hi Andrew, No problem, I too have found it very interesting and infomative. It just goes to show how [ when using top class ER collet chucks ,collets and closers ] just how accurate the system is. The TIR figures that one can look forward to seeing are superb. Iv'e always been a fan of the ER system even for workholding, although im not blind to the fact that there are collet systems that are better for that aspect. The biggest bugbear I have with it from a "workholding" aspect is it's not very good at short length parts [parts always must be inserted at least 2/3ds of the collet length] although that can be solved by turning a plug the same Ø as the part. Its just not very convenient.

I am now going to try and find out the " bore tolerance " to try and answer John's query.

cheers

[Neil WyattModerator @neilwyatt]

In my experience ER collets are a 'push fit' on cutters with the matching nominal diameter. Given the inherent flexibility of the collet, I would be surprised if they are toleranced to be bored oversize.

It will be interesting to see what you find.

Perhaps a short article for MEW summarising all this information could be a useful outcome of this thread?

Neil

[Martin ConnellyParticipant @martinconnelly55370]

Tormach have investigated pull out values for collets. Their report is useful reading for anyone using collets.

**LINK**

The important point for this thread is suitable lubrication on the correct surfaces. I wonder how many of these run out checks are being carried out with suitably lubricated surfaces. It may make a difference to the TIR values. It would be a good subject to include if an article is written for MEW as suggested by Neil.

Martin

[Raymond AndersonParticipant @raymondanderson34407]

Hi Folks, I could put the pdf of the ISO 15488 / Din 4699 into a album but i'm not sure how. So in answer to Ajohnw's question re bore tolerance,, The bore of an ER collet is to H7 tolerance.

Also as an aside, you can also get "ETS " collets which fit into an ER chuck, but use a different closing nut [same threads obviously ] The accuracy is slightly better than ER collets

cheers.

[Author]

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