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ER32 Collet Chuck

Myford S7

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Peter Love 119/01/2019 16:58:13
16 forum posts
2 photos

Hello someone may be able to pick the bones out of this.

Not wanting to buy a cheap Chinese ER32 collet chuck for my S7 I bought one from Luxembourg with postage about 85 Euro's, very disappointed it did not screw down to the register by about 2mm, after fixing the problem by boring the hole back a bit more the run out was 3 thou' on the body and the collet taper, ( My lathe I will add has a zero run out on the spindle) with the collet chuck screwed in place I retouched the the taper to a perfect zero and also the taper in the retaining collar nut, however, the chucks body is still running out and there is not much I can do about that, when a collet is fitted the run out is 2 thou' so I can only assume that the collet is being pulled by the non concentric body. Any thoughts would be welcome while I carry on producing my own and with any luck as it is being produced in place on the lathe should be perfect.

Tony Pratt 119/01/2019 17:12:25
990 forum posts
3 photos

Your collet chuck from Luxembourg is likely to be a cheap Chinese import, if the taper & retaining nut are now running true I don't see how the non concentric body is the problem as ER collets are guided by these 2 features, are the collets any good?


John Haine19/01/2019 17:22:37
2836 forum posts
141 photos

To be honest Peter I can't work out from your description exactly what you did. Is this a chuck that screws on the spindle nose or does it have a taper shank? If the former the ones I am familiar with are in two parts, one you screw on the spindle nose first then turn a register true to fit the second part that has the active taper.

But they are pretty easy to make so if you turn one in situ on the lathe it should be fine, but you'll probably need a new nut if you've "retouched" the taper in the nut.

This demonstrates yet again, if you buy something new and it isn't satisfactory SEND IT BACK, don't try to correct it, it just encourages sellers to keep supplying crap.

Emgee19/01/2019 17:25:20
1361 forum posts
212 photos

Hi Peter, not much consolation now but after finding the chuck did not screw on the spindle properly you really should have advised the seller of the faulty goods, now you have machined it I suppose you are on your own to effect a remedy.
If you have trued the collet seat to no run out and you have 2 thou run out with a collet fitted like Tony I would suspect the accuracy of the collet.


Peter Love 119/01/2019 17:34:50
16 forum posts
2 photos

Hello Tony thanks for your reply just what I was hoping for someone to suggest something I may not have thought about, you may well be correct the set I have were about £130.00 from RDG, however, turning a collet to all points 360 deg’ makes no difference what I am thinking is the thread for the collar nut will not be in the centre of the tapers and therefore not be pulling down square to the tapers.

John Haine19/01/2019 18:26:37
2836 forum posts
141 photos

There's been a recent thread about ER collets and the influence of how they are tightened on runout. They need to be very tight, and the torque applied as a couple not with a wrench that also pulls the nut sideways which can pull the collet over. I now use a deep socket to do this.

SillyOldDuffer19/01/2019 19:23:38
5149 forum posts
1074 photos

I'm a bit confused by the description too. A photo would help.

I think Peter means the chuck isn't screwing down to the lathe's register, which strongly suggests a poorly made chuck.

But if he meant the collet isn't screwing down properly into the collet chuck, that opens the possibility of operator error. On first meeting with ER collets it's not unknown for chaps to miss that they go into the screw-ring at a particular angle and then click into place. It is possible to tighten them up wrongly leaving a misaligned collet sticking about 2mm outside the chuck. Don't ask how I know...


Neil Lickfold19/01/2019 19:46:42
585 forum posts
102 photos

So, if you now have it correctly registered on the spindle nose. Also you have re turned the inner 8 deg taper per side. If this is correct, then the next area of error is the thread for the nut. If the thread for the nut is not concurrent to the 8 deg taper, it will not work correctly either. The thread will be a 1.5mm pitch thread. So can be recut again with care.

Then you have the collets and collet nut itself to sort through.

As simple as the ER system is , for it to work properly, it all needs to be concentric and true.


peak419/01/2019 20:16:00
989 forum posts
98 photos

I recognise the problem exactly as I recently bought an ER25 version from the autojumble at Newark.

It was apparently new, was fully assembled, and looked in good nick, but ran out by a good 10 thou.
For those who haven't seen one, the chuck comes in 2 parts + a nut, one spindle nose adaptor with a register boss (mine is a black knurled body) and a separate chuck, tapered on one sire to take the collet and bored the other side to fit the spindle nose adaptor.

When I investigated, I found that the previous owner had done the same as I think you appear to have done.
It's quite intentional that the hole on the back of the chuck part is too small for the boss that sticks out of the lathe spindle part, when the kit is originally supplied.

The intention is that you treat it like fitting a normal 3/4 jaw chuck to a backplate.

In this case, fit the black knurled bit to the spindle, and reduce the boss down to the correct size for the precision made chuck to fit it.

Alas, if I read your problem correctly I think you bored the hole to suit the register on the knurled bit, and your chuck has a taper which is no longer concentric with the hole in the back of it.

Mine is both off-centre and also at an angle.

We are now in the same boat and I'm looking for inspiration on the best way of fixing it.

So far I've tried turning a new larger diameter on the register on the knurled bit. I then took a length of ground round bar and clocked it up in a 4 jaw with a tenths clock, until I has a zero runout reading along a decent length of the bar. Next up I picked a suitable collet, fitted it to the chuck and clamped the assembly to the bar, with the rear hole now facing the tailstock, thus I could re-face the flat and re-bore the collet chuck's rear hole, exactly concentric with the ground bar. Everything was scrupulously checked for burrs and cleaned thoroughly.

The finished boring and facing was again checked with a tenths clock and showed perfect.

Now I reversed the whole collet chuck setup and turned the boss on the knurled bit to suit the concentric bore I'd just made.

Bolted everything up and re-clocked it; looking good now, but only initially.

Trouble is that every time I try a different collet or bar, it's a mile out; I can only assume that the cheap Chinese collets just aren't sufficiently accurate/repeatable to to hold the chuck in this reversed manner to try and re-machine it concentrically.

I've also tried making the chuck a looser fit on the register, with slightly bored out mounting holes for the allen screws This has allowed be to gently knock everything into alignment to get a near zero runout by the chuck, but the tailstock end of a bar in a collet still wobbles too much, so clearly I've not been able to get the interface square enough.

Note also that the bottom of the mounting holes in my chuck hadn't been spot faced. They were still conical from the original drilling, hence when I tightened the allen screws, they pulled the chuck off-centre.

Still seeking inspiration, before I remove even more metal. Latest thought is to try soft jaws in a 3 jaw, machined to hold the register just where the main nut thread finishes, and try re-facing from there.


Edited By peak4 on 19/01/2019 20:19:55

Edited By peak4 on 19/01/2019 20:25:19

Chris Trice19/01/2019 20:42:37
1362 forum posts
9 photos

Let's not be too down on the Chinese. If it's a Soba one or from the same factory, it's Indian. The one I bought (what was I thinking?) would not fit the lathe register. It was a good ten thou undersize. I couldn't be bothered. It went straight in the bin.

peak419/01/2019 20:48:53
989 forum posts
98 photos
Posted by Chris Trice on 19/01/2019 20:42:37:

Let's not be too down on the Chinese. If it's a Soba one or from the same factory, it's Indian. The one I bought (what was I thinking?) would not fit the lathe register. It was a good ten thou undersize. I couldn't be bothered. It went straight in the bin.

My collets were definitely from China, no idea about the chuck, but I can't blame the manufacturer for the previous owner's machining when they tried to assemble it.


Peter Love 119/01/2019 22:06:37
16 forum posts
2 photos

I have added a couple of pictures of the chuck, you can just see the serrated mark where I removed about one thread for the chuck to hit the register.



John Reese19/01/2019 22:24:57
818 forum posts


I really wish you had put the photos in your original post. As Emgee said, you really should have returned the chuck. Now that you have modified it I think you are truly screwed.

peak419/01/2019 23:57:38
989 forum posts
98 photos

Would have saved me a bit of typing the above, though I'd still appreciate some ideas in my circumstances.

I do appreciate it takes a while here to work out how on earth to post a photo.wink

In your case, you've presumably only removed some of the thread, rather than the diameter of the register.

Really the thread only holds it on, and the bore sets where its sits axially. Have you had a play with some Micrometer Blue to make sure you have a good symmetrical fit, on the rear flat annular surface, the threads themselves, and the bore of the chuck?

Maybe chuck up a length of straight ground bar and measure the run-out against a mark on it. Take the whole assembly off, with the bar still chucked up, re-fit and re-measure. Is the error still in the same place with respect to your marks.

Keep the collet, bar, and chuck in the same orientation with respect to each other, loosen and re-torque, has anything changed?

Keep the collet in the same orientation with respect to the chuck twist the bar and re-torque, has anything changed etc?

Continue until you can replicate the exact same error, in both magnitude and direction repeatedly and then have a further ponder.

I know it takes a long time, I'm right there at the moment. frown


Edited By peak4 on 20/01/2019 00:01:27

Chris Trice20/01/2019 01:29:11
1362 forum posts
9 photos

The chuck does look like a Soba.

Peter Love 120/01/2019 08:51:32
16 forum posts
2 photos

Hi all, once again thank you all for the replies I have had so far re the ER32 collet chuck, I can say definitely that the problem with the chuck initially not reaching the register was that the thread on my S7 had been cut slightly too short at the register end, this caused the thread in the chuck to reach its limit before hitting the register, so, removing a tad of the chuck thread fixed the problem perfectly.

I have picked up on John's post about a thread that referred to the tightening of the collet collar nut and how it might influence the collet position, I am after all now only looking for 2 thou', so, before I proceed with the chuck I have started to make I will unscrew the 4 jaw complete with the workpiece and give the problem collet chuck one last chance by giving it a damn good tightening and report back.

Kindest regards all, Peter.

Russell Eberhardt20/01/2019 09:38:26
2540 forum posts
85 photos

How tight is the tread on the closing nut/body?

It needs some slack otherwise any out of true on the thread can pull the collet out of alignment.


Chris Trice20/01/2019 11:26:06
1362 forum posts
9 photos

Assuming you can get the accessory to fit its intended victim, I'd be inclined to carefully and minimally remachine the taper and screw thread so everything was all concentric. You shouldn't have to but since you're already down that road... Cocentricity is more important than any additional slackness in the closing thread providing you don't make it so slack the threads are likely to fail completely and assuming the closing nut is manufactured accurately.

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