Special ER Collets

[Neil WyattModerator @neilwyatt]

The ratio of bore to supported length is important.

Neil

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Neil Wyatt on 07/04/2016 20:00:14:

The ratio of bore to supported length is important.

Neil

Please explain. What is the effect if the ratio is wrong?

Russell.

[Michael BriggsParticipant @michaelbriggs82422]

If I need to hold a short workpiece in an er collet, I put a short piece of the same diameter in the back of the collet as Gordon and Michael have said, works a treat.

Edited By Michael Briggs on 09/04/2016 10:16:51

[Michael GilliganParticipant @michaelgilligan61133]

Here is a useful collection of information:

**LINK**

The comment about the holding capacity of ER-MB collets is interesting.

MichaelG.

.

P.S. Here, for Lottery winners, is the Regofix catalogue.

The warning on p24 of the PDF is pertinent to this thread.

Edited By Michael Gilligan on 09/04/2016 11:14:25

[Howard LewisParticipant @howardlewis46836]

Russell,

Length/bore ratio

Just think about pulling sideways on the top of a 1 metre post that is 10cm into the ground. It will wobble!

If you are lucky, the short work won't come out as you cut!

Howard

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Howard Lewis on 09/04/2016 12:47:25:Just think about pulling sideways on the top of a 1 metre post that is 10cm into the ground. It will wobble!

If you are lucky, the short work won't come out as you cut!

I wouldn't call a 1 m bar short! My point is that ER collets maintain parallelism as they close so there is no point in putting a supporting piece in the rear of the collet.

No luck involved, just usual care.

Russell.

[Douglas JohnstonParticipant @douglasjohnston98463]

I am not so sure they can maintain parallelism if there is only contact at one end. You may well be right Russell but I can't help feeling the need to support the other end.

Doug

[Neil WyattModerator @neilwyatt]

Posted by Russell Eberhardt on 09/04/2016 10:01:42:

Posted by Neil Wyatt on 07/04/2016 20:00:14:

The ratio of bore to supported length is important.

Neil

Please explain. What is the effect if the ratio is wrong?

Russell.

The leverage a part in a collet has that allows it to distort the collet depends on the supported length. Smaller parts have less strength and will bend before they distort the collet so they don't need as much support.

Neil

[Roger HeadParticipant @rogerhead16992]

Posted by Michael Gilligan on 09/04/2016 10:56:44:P.S. Here, for Lottery winners, is the Regofix catalogue.

The warning on p24 of the PDF is pertinent to this thread.

Edited By Michael Gilligan on 09/04/2016 11:14:25

Well spotted, Michael. Makes sense, really. (For others, it's p3 of the catalogue numbering, p24 of the pdf file). Not normally a problem for toolholding, but a definite concern for holding short workpieces. Rationally-priced ER collets are lax enough in their run-out performance without adding our own distortions.

Roger

[John HaineParticipant @johnhaine32865]

I think a factor must be the different tapers on the front and rear of the collets. I suspect the closing force at the rear is greater as the taper is more gradual and friction between the socket and the collet less significant. The front taper is much steeper. Imagine that the taper was actually 90 degrees at the front, there could be no closing force. So a short workpiece that only enters the front of the collet may not be held so tightly.

[Neil WyattModerator @neilwyatt]

Looking at Michael's link what always fascinates me is that the tightening torques for collets are (at the recommended 80% of maximum) comparable to what you would use for diesel engine cylinder head bolts…

Hands up anyone here who pulls over 100lbs on the end of their 8" long ER25 collet spanner?

Neil

[Peter KroghParticipant @peterkrogh76576]

Posted by Neil Wyatt on 10/04/2016 08:44:02:

Looking at Michael's link what always fascinates me is that the tightening torques for collets are (at the recommended 80% of maximum) comparable to what you would use for diesel engine cylinder head bolts…

Hands up anyone here who pulls over 100lbs on the end of their 8" long ER25 collet spanner?

Neil

I'm looking at ERs for my little mill, and was shocked when I saw the torque spec for an ER-32 nut!!

I'm with Neil in asking this question…..

Pete

[Gordon WParticipant @gordonw]

Maybe the torque setting is the max that the threads will stand ? I have a ER32 ( best thing I've bought, so far ) And usually just hand tighten the nut, holding the spindle with a tommy bar. This is for workholding not toolholding.

[Anonymous]

Posted by Neil Wyatt on 10/04/2016 08:44:02:

Hands up anyone here who pulls over 100lbs on the end of their 8" long ER25 collet spanner?

I don't faff around with a mere 8 inches. I use 12" spanners on my ER20 collets. Of course I only use them for tool holding, and that I think is the point. Milling cutter shanks are hardened so the gripping force relies almost entirely on friction. To obtain a high value the nuts need to be done up very tightly.

Andrew

[egaParticipant @ega]

My ER40 collet spanner is getting on for 1' long.

[Neil WyattModerator @neilwyatt]

I use a puny 4" tommy bar and an 8" c-spanner with as much force as I can muster, but nowhere near 130Nm on such short tools. the tommy bar is an 'interesting' shape.

Neil

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