Excentric collet

Hi Michael, just noticed your post I will go have a look at the document. and yes It is an interesting discussion.

Cheers.

When I first got ER collets I found they had terrible runout.

Took a while to figure out the colled should be "clicked" into the nut.

Hi Michael, Just read the document and although I was aware of the NO oversize shanks It is still the grey area as regards the part "over the entire clamping range " but hopefully the makers I mentioned will respond and there will no longer be a "grey area" Re your Burnerd Multi size chuck, although Iv'e never had or used one the brother has, and he was saying that it is a good system , very versatile and robust. if that is the same system as you had then there are square and hexagonal collets also. Pity you sold it, although we can all be wise after the fact.

Cheers.

Some time ago I made the mistake of buying a SOBA branded Myford nose mounting ER25 collet chuck from one of the Harrogate exhibitions. I left it too long after purchase to try the thing on the lathe, to find that it didn't fit, to send it back & this thread prompted me to ave another look at it yesterday. lt looks nicely finished, but would not screw fully onto the spindle nose. A couple of hours lapping with fine paste opened up the apparently tapered bore such that it now screws up to the spindle location shoulder without binding. Applying a dial guage to the collet taper shows 0.07mm runout - I guess that I need a toolpost grinder now to true up the collet taper in-situ.

Non of this has any bearing on the original query but, despite the runout, I mounted a ground 12mm pin in a used 12-11 collet (ex industry) using the SOBA supplied closing nut. Runout approx. 20mm from the collet measured 0.15mm. A new Chinese 12-11 collet was tried, with similar results. I had an ex-industry German Zuern closing nut to hand - a bit grubby, but a squirt of brake cleaner got it looking presentable. Using the same Chinese collet & same pin with the Zuern nut gave a runout of 0.075mm - almost identical to the collet bore runout on the chuck. So it would appear that the nut can have a large influence on the gripped tool runout, all other factors being equal. I didn't have anything accurately ground 11mm diameter to hand to see what effect closing the collet down to it's minimum diameter had on runout.

The SOBA nut does not, on the face of it, appear "badly" made, with the main difference being the German nut has a ground thread and collet closing face where the SOBA is just turned & blacked.

Interesting to see in the Regofix catalogue linked to earlier that the range includes 0.5mm increments as well as 1mm - I wonder if the more restricted operating range collets perform better for runout than the "normal" range when closed down ?

Nigel B

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.

Hi Michael G, until I hear back from the makers I have contacted, there is an interesting piece of info from 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

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.

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

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.

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Thanks, Raymond

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

Much appreciated.

MichaelG.

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

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 ]

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

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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.

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.

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

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.

.

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.

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

MEW 232 page 34.

Neil

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

MichaelG.