ER 32 Collet Tightening Torque.

Recently, looking at ER 32 nuts with a ball bearing to reduce friction and increase clamping force (ARC and others sell them) got me thinking about how much torque should be applied when tightening an ER 32 collet.

After a bit of searching around the internet and looking at various manufacturers web sites it became clear that the standard figure for ER 32 is 100ft-lbs / 140 Nm.

From experience in my youth of working on cars and engines that it a lot of torque. Given the relatively short length of the standard collet nut spanner there is no way I could now ( in my dotage) exert that kind of torque, particularly with the collet holder mounted in the spindle. And, even if I did manage to torque it up that much I don't think I would ever get it undone again.

Anyone care to give comment?

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The numbers look valid ... so the problem is real

That’s one of the reasons why some of us still prefer traditional ‘fixed size’ collets

MichaelG.

A spanner (Home made in my case ) to fit the flats on the holder, and a hearty blow with the other hand on the C spanner supplied usually suffices.

Ditto for slackening

Howard

I use er25 and have a ball bearing nut, which should allow a reduction of 1/3 of the torque. The torques quoted are for the maximum size cutters, so if using an 8mm one, you could use half of the maximum amount. I have put spanner flats on the er body, (the current ones seem to have them from new),and have milled the jaws of a foot long spanner to match. The nut wrench is pressed into a foot long steel tube, and together, they make tightening and loosening easy. With er, it is always a good idea to have a folded up old towel underneath to catch the cutter as you break the collet taper.

Torque?? You would need a torque wrench to measure torque applied, why? In my mid seventies I just tighten by hand and have never had a cutter slip.Its a fair question but sometimes I think it's to easy to make things more complicated than they need to be

Mick 🇫🇴

As most of us don't take cuts that are anything like as heavy as industrial users do there is less need for us to use long handled torque wrenches and hefty bench mounted fixtures to hold the chucks in while tightening. Though there will be a lot of variation between what individuals can apply given the same pair of spanners which may be why some on here say ER collets let tools slip while others including myself have never had a problem..

Michael, have you tried Nominal size only ER Collets rather than collapsible ones

Edited By JasonB on 28/09/2020 18:29:24

Maximum tightening torque is more of a CNC issue than one for the likes of us.

Due to alignment being partially dependent on the (relatively) loose fitting nut high tightening torque is essential if any hard working cutter in any collet is to be in dead nuts alignment every time. The potential errors involved when tightening enough to hold the cutter at home shop feeds'n speeds in comparison to doing it by the book are probably well below anything we can reliably measure. Certainly not enough to worry about in our typical one at a time work.

CNC machines work their cutters hard so pullout can also be an issue. With no positive retention, like a Clarkson thread, the collet has to be tight enough that the cutter always stays put for the whole job. As ever there is a considerable step up between "always right" and "usually just fine". Mighty Big Industries and, these days, Joes Local Precision CNC shop have to be at the "always right" end of the curve to minimise scap and do-overs. Both, at best, expensive. Us not so much.

Although a cutter pulling out mid job is, I find, an excellent stimulus to verbal creativity.

Realistically something around 1/4 to 1/3 book is probably acceptable. Which, for ER32, gets you into the same sort of range as the 30 - 35 ft lb Bridgeports used to suggest for the R8 collets. As a pragmatic sort I can live with that.

Clive

Get a longer spanner? End of problem.🙂

Good commercial machine shops likely always torque the nuts when changing the cutter. Off the machine, not on it - like most of us do it.

How much torque reduction do we get for using a bearing nut?

Comes down by about 1/3rd for a bearing nut, Rego Fix give 100 plain nut and 65 bearing nut for the same dia bit in an ER32

Thanks, Jason.

This is what I use for ER32 nuts. I recommend avoiding any wrench that is hard on the hands such as combination or double ended. Keep the collet and tool oil free but have a fine smear of oil on the inside taper of the holder and use ball bearing nuts.

Martin C

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No ... but presumably that would not require the high torque that collapsing by a millimetre would.

[ and therefore would not be particularly relevant to the OP’s question ]

MichaelG.

Drifting OT a bit  and further sidestepping the torque question I'm inclined to think that if you are going nominal size a side-lock is better and better value for money.

Given that, generally, milling cutters only come in a few shank sizes it seems a little strange to advocate ER collet sets as a general purpose solution for the ordinary ME / Home Shop guy or gal who always needs every £ to do the work of £5 or £10 or even £ lots if that can be arranged.

I bought into the "ER 32 set on an R8" ethos way back with very workmanlike kit from Vertex. Mostly unused and even the ones that were saw little action as a Clarkson was much better fit for me. Nowadays native R8s do simple collet duties in the Bridgeport.

I've long considered that economically priced, say 3 or 4 in a box, sets of side locks in the "shank sizes you use" would be a better fit for ME and HW folk. Keeping the cutters you are using ready to go on a shank like a CNC is just as useful in the home shop. We may not have production demands but there is never enough time.

But such sets would be essentaily unsaleable!

Clive

Edited By Clive Foster on 28/09/2020 20:49:56

Edited By Clive Foster on 28/09/2020 20:50:51

at 76yr old I don't have a problem at this time but have given the process some thought for the future
Remove ER32 holder from mill spindle and assuming it has spanner flats on it,.place in vice and tighten up on the flats. Insert collet in ER nut, screw nut down on holder finger tight, insert cutter then apply 4-prong spanner to ball-bearing nut and tighten, two-handed on the spanner is now possible, wrapping spanner handle in cloth may help. This will be much easier than doing it two-contra-handed in mid-air on the mill whilst hoping the cutter doesn't fall out in the process. A rubber/hide hammer may assist with tightening/undoing the nut with the spanner.
As mentioned above, the ball-bearing nuts really do make a difference.
DaveD

Edited By Meunier on 28/09/2020 21:15:40

I use ball bearing nuts with spanner’s very similar to Martins and don't normally have any problems except when threading on the lathe. Taps and dies seem to be able to produce a surprising amount of torque even with a suitable lubricant.

Be cautious when using "torque" to measure fastener tension (because ultimately, that's the aim of the game). Several factors can affect it. Namely, torque wrench calibration, fastener material, cleanliness and lubrication. These factors may well be more significant on smaller fasteners, You will find specific torque figures for certain materials and lubricated/un-lubricated. Not sure about lubricating the taper though?

This is nothing to do with fasteners and all to do with driving the collet up into the taper of the holder with enough force to compress it sufficiently onto the shaft of the item in the collet. A compressive load not a tensile load.

Martin C

Yes, but it's the tensile force between the nut and holder that provides the radial compressive force via the taper. OK, it's hyjacked the thread a bit, but still relevant non the less.

Conflation

Martin C

I use long extensions to make life as easy as possible, having acquired mechanical sympathy I don’t use long extensions to over torque things just to make life easy. The tightest nut I have encountered was the front wheel bearing on a Maxi, even when I was strong as an Ox it took a four foot long extension to undo it. So far I have not had a problem with ER25 nuts and I doubt that I have reached the recommended torque but I do give them a good grunt tighten. A good strong spindle lock is helpful as is not so easy to use two spanner’s at the limit of your strength. It is easier to tighten off the machine but if you need to change the cutter often this can be tiresome.

Mike