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Collet runout. Is this normal

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JDS28/01/2021 15:49:35
16 forum posts

Hi everyone.

Still new to lathe work but having fun playing.

I have bought an ER32 collet chuck from RDG and a set of DIN6499B collets from gloustertooling for my Myford S7

My spindle has less than 0.0005" runout.

I cut the face and register in 1 go on the backplate and then fitted the chuck.

I have 0.0005" runout on the chuck taper so I was pretty pleased with that


When I measured a ground 6mm pin the the collet I am getting 0.0015 runout right at the collet face and 0.0035 about 50mm out from the collet.

Is this ok or normal? Is this within tolerance for DIN6499B collets?

Have I screwed something up and can I fix it ?

Pointers and advice gratefully received


JasonB28/01/2021 15:59:35
21327 forum posts
2424 photos
1 articles

Have you snapped the collet into the nut correctly before doing it up?

Thor 🇳🇴28/01/2021 16:01:00
1397 forum posts
41 photos

I made my own collet chuck for my Emco C8 lathe and I get about 0.02 mm runout using my best collet, so a bit better than yours. My worst ER-32 collet gives about 0.03mm runout. The seller of my best ER collets says max runout of collet is 0.015mm. Have you tried with other collets?

If you mout your 3-jaw and chuck a piece of mild steel and turn it down to 20mm and mount your ER chuck (without backplate) on the turned rod and measure the runout at the rear of the ER chuck, you can check if there is runout between collet and chuck and the mounting flange of the ER chuck.


JohnF28/01/2021 16:02:45
1095 forum posts
172 photos

I don't know the tolerance for the DIN spec you quote but I would be disappointed and expect better results. However collets are made in varying qualities thus giving varying results.

The first thing I would do is repeat the test with several other collets using nominal sizes, 8, 10mm etc, if the same result is shown then suspect the chuck, if results are better then you may well have a duff 6mm collet.


Howard Lewis28/01/2021 16:11:40
5241 forum posts
13 photos

Previous post on the Forum have said that the toque applied to the clamp nut can affect runout. i.e. the tighter the nut, the less the run out.

So was the nut pulled up as tight as possible?

It might be interesting to compare results with varying amounts of tightening.


not done it yet28/01/2021 16:34:18
6285 forum posts
20 photos

You say a 6mm pin but quote runout in inches. Were you using a 1/4” collet? If so, the declared maximum runout will be for the nominal size of the collet.

JDS28/01/2021 17:22:27
16 forum posts

Hi guys thanks for all the ideas.

I have tried a few of the collets and it is pretty much the same. Tightening the collet nut more did help a bit but I did not want to over do it.

but that got me thinking I looked at the nut and saw this ( photo below) bit I don’t know if this is how it is supposed to be as I have never seen on before

It does not look right to me

JasonB28/01/2021 17:25:43
21327 forum posts
2424 photos
1 articles

Picture not showing up but I suspect you can see a hole with an offset cut out this is so the collect can be snapped into the nut so I will ask again are you correctly fitting the collet into the nut before screwing the nut onto the chuck. If you don't do that it will push the collet sideways and give the measurements you are getting.

The nut should also pull the collet out of the chuck when undone, if the collet is staying stuck in the chuck that is an indication you have not fitted it correctly into the nut.

See pic at the top of this page the lip at the bottom of the section through the nut is smaller than the lip at the top.


Edited By JasonB on 28/01/2021 17:32:58

SillyOldDuffer28/01/2021 17:42:50
7487 forum posts
1658 photos

JDS: can you have another go at posting the picture please? How to is described here. This forum's a bit different.

ER collets are a little awkward to mount correctly. They go in at a slant and then click upright and down on to the face. See ArcEuro's website for a good description.

Doh; I've just noticed Jason has already provided the same link.  


Edited By SillyOldDuffer on 28/01/2021 17:44:20

JDS28/01/2021 17:44:13
16 forum posts

laugh Cheers Jason that funny you knew what i was asking even though the photo did not work.

That was excactly what I was worried about but at least i know mine is ok.

The collets locate in the nut ok and when tightened they are pretty much flush with the face of the nut.

I think i will strip it down and try again. I will let you know what i findyes

not done it yet28/01/2021 19:28:01
6285 forum posts
20 photos

I did not want to over do it.

What torque did you tighten it to? For a normal (non-bearing) type nut, the proper torque figure is likely around 135Nm.

JDS28/01/2021 19:59:25
16 forum posts

Wow thats high. I did until the c spanner did not move any more, but it's handel is only about 100mm long so i gave it a tap with the hammer.

Sorry not scientific but it was pretty tight.

I think the chuck might have runout.

I re-cut the backplate and it has less than 0.0005 runout, but when i mount the chuck on the backplate the face of the chuck thread is 0.002 although the taper is 0.0005 how is this possible.

Also if i rotate the chuck on the backplate to the next bolt hole the reading stays the same

Thanks for al your help

Oily Rag28/01/2021 20:34:35
464 forum posts
147 photos

If you have failed to seat the ER collet correctly previously there is a good chance the collet is now bruised and the snap ring damaged. If that is the case you will have to scrap the collet(s) affected and invest in a new nut.

If you do buy a new nut go for a quality job like a Rego-Fix nut with ball race seat.

Andrew Johnston28/01/2021 20:54:05
6237 forum posts
676 photos
Posted by JDS on 28/01/2021 19:59:25:

Sorry not scientific but it was pretty tight.

Not scientific nor tight. smile

Remember that ER collets were originally designed for holding tools not workpieces. The torque required for closing is high and if not fully applied then runout is anyones guess.


JDS28/01/2021 21:01:14
16 forum posts

yesSo what technique do you guys use to tighten the nut. how do you mesure the torque I have a 1/2 drive torque wrench but i can think of a way to use that with a c spanner

JohnF28/01/2021 21:33:37
1095 forum posts
172 photos

JDS said

When I measured a ground 6mm pin the the collet I am getting 0.0015 runout right at the collet face and 0.0035 about 50mm out from the collet.


In a later post you say the other larger collets are pretty much the same - are you saying they all have .0015 at face then .0035 at 2” or50mm from the collet ?

If this is so it would suggest the collet location taper is at an angle to the machine spindle axis ? To prove this Thor’s suggestion will assist.


Neil Lickfold28/01/2021 21:38:54
720 forum posts
127 photos

ER collets are a bear. I have lately been buying the high precision ER collets from Regofix, the inventors of the collets. The inner taper is 8 degrees taper per side. It just happens that what is really important on the ER system, is that the Nut thread is concentric to the inner 30 deg per side taper. So you could have a bad Nut. The Spindle or the part with the inner 8 deg taper per side, also requires that the thread is concentric to the inner taper. If any of these are out, the collet does not work properly. It is easy enough to recut the inner 8 deg taper. The recut of the outer thread form is a little more difficult . It is 1.5mm pitch thread. you can check the concentricity of the outer thread by hand rotating the spindle like cutting a thread, but use a dti in the thread form to how it is. Thread fit is not that critical, better to have a loose concentric thread, than a good thread that is not concentric to the inner collet bore. The Regofix nuts are really good. I have had some ok success with ER nuts from other makes. Good collets should be around 0.01mm TIR total indicator run out. 50mm out from the chuck up to 0.02 is acceptable. Very good are less than 0.005mm TIR . You can lightly tighten, and gently knock in the runout at the end of a part, and then tighten. The part will run true of the collet is good to start with. I did buy some cheap collets that were useless. So have binned them. They had lots of issues, so were not concentric with the 30deg taper and the 8 deg taper. Also the inner bore was a long way out of concentric and was on an angle to the main 8 deg taper. So no chance of reworking them to a useable collet. Sometimes a out of concentric 6mm collet can be reground and made into a 1/4 inch collet etc. The smaller you go, the harder it is to correct the bore. Lots of time can be easily wasted with badly made tools. I have not found that the over all tightness of the collet nut to be such an influence on the concentricity of a collet.

Edited By Neil Lickfold on 28/01/2021 21:41:29

Oily Rag28/01/2021 21:53:58
464 forum posts
147 photos

+1 for Neil's comments. There is a lot of Far Eastern tosh around which is utter rubbish - I am lucky in that no one in the Far East makes ER holders that fit my machine. As it is a Schaublin W20 taper the only people that do these style arbors / ER collet holders are Rego-Fix, expensive but absolutely accurate and more to the point repeatable accuracy to the extent that a removed tool to allow headroom for measuring a bore when replaced was within 0.0002" of original position.

For repeatability like that I don't mind paying.


Bill Phinn29/01/2021 00:39:46
563 forum posts
86 photos
Posted by Neil Lickfold on 28/01/2021 21:38:54:

I have lately been buying the high precision ER collets from Regofix

Would you mind telling us where Regofix products are to be had in the UK, Neil, assuming they are?


JasonB29/01/2021 07:09:44
21327 forum posts
2424 photos
1 articles

Have a look at this about 15mins in for tightening. I doubt many in the home workshop use the end fit type torque wrenches let alone a tightening fixture. I would not be hitting the C spanner with a hammer or any spanner for that matter. The rest is worth watching too.

Edited By JasonB on 29/01/2021 07:10:22

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