Arc Euro ER16 runout

I've just finished making a backplate to fit one of the Arc Euro ER16 collet holders onto my Unimat SL.

Along with the collet holder I also bought a 1/8 collet so that I could see if they were any good before considering a full set of metric collets.

Measuring the runout inside the holder with the nut off I got 1/2 thou... more than I was hoping for but not terrible.

Clamping a Proxxon milling cutter as a test piece and checking the runout on the plain part of the shaft proved less than encouraging - 3 thou runout... which is no better than my 3 jaw chuck.

I also clocked the inside of the nut bore with the nut tight and no collet in the holder - this came out at 5 thou.

I'm not sure if the problem is with the collet or the nut but the runout inside the bore of the nut seems like A Bad Thing to me.

I have a friend with some ER16 collets so I may be able to try some of his in a few days time. I dont know if the nuts are interchangeable... we shall see.

Have I bought a dud? Does anyone else have experience of the Arc Euro ER16 collets and collet holder?

Regards, Andy

[edit: typo]

Edited By Andy Carlson on 08/12/2018 22:59:10

Always use a machined in place mounting plate for chucks and collet chucks, it's the only way you can get perfect results, as any lathe user will know.

I'd suggest trying again, but pay special attention to cleanliness of the collet and the holder. Any trapped swarf will play havoc with concentricity. Also, try to use these ER collets at full capacity, e.g. install a tool with a 6mm shank in a 6-5 collet, rather than something with a 5mm shank, where possible.

Edit: You did install the collet into the nut correctly didn't you?

Installation link

Martin.

Edited By blowlamp on 08/12/2018 23:27:24

From memory the SL lathe has a M12 or M14 threaded spindle nose so have you made a backplate that screws onto that and then has a register to suit which Arc collet holder?

I can see why using collets is a good idea but for an SL to take ER25 a lot of mass and overhang is inevitable and is going to take away some of the benefits. Even so the run out you mention is more than I would expect but from your description its not clear what is causing the problem. You need to go back to basics and measure the runout in stages starting withe the spindle nose itself.

Ian P

Two things:-

1. You should be able to adjust your backplate to zero runout. Verify that the runout is zero,or at least identical, at both the front and the rear of the taper, that will ensure that you haven't got the collet holder mounted at an angle (fixing an error here would take some maths and patience).
2. Are you certain that you inserted the collet into the nut correctly. Sorry if it's teaching grandmother to suck eggs, but the collet needs to be hooked into the off-centre washer in the nut before mounting in the holder. This is the number one cause of mis-alignment in ER collets.

The nuts are interchangeable .

Thanks for all of the replies.

Yes, it's a backplate to screw onto the M12x1mm SL spindle thread with a register and 3 screw holes to suit the Arc collet holder... and ER16 not ER25.

I didnt mention but the final turning of the register diameter and facing of the mounting flange was done on the Unimat. The clock gauge needle was rock steady on both surfaces and the fit between the backplate and collet holder is good.

After posting I also dug out a 3.2mm drill and tried that too.

With the nut a very loose finger tight the runout was around half a thou. With the nut a firm finger tight the runout increased to around a thou.

I'm suspecting the nut at the moment.

And I clipped the collet into the nut first... and checked for muck... and tried several times to make sure I got the same result

Regards, Andy

What do you get when fully tightened?

The closing nuts do float on their thread, which may account for the runout you can see.

One area where ER collets fail is if they're used with an insufficient amount of tool shank entered into them. If you try to grip a part with just the front of the collet, the back end collapses in through lack of support and everything goes to hell.

Martin.

Martin.

Technically this shouldn't make a difference but I've found sometimes it does. Gently tap the cutter all the way around with a rubber hammer and reposition the spanner that does the nut up on the other side of where you originally did it up to do it up further. The only reason for this working can be that there are tiny differences in taper between the collet and the chuck and/or the nut (assuming everything is spotlessly clean and oiled). Most people's first thoughts would be "cheap collets" but a little gentle tapping and further tightening can seat the cutter exactly where it should be, showing that in fact there is no "fault" with the collet and for some reason the cutter has simply failed to find its perfect position first time.

You also need to do them up tight, more than you can with the little tommy bars that come with Unimat chucks.

I'd try with another collet and if you can also borrow his nut to see if that is where the issue is would be helpful. A bearing nut makes doing things up easier and there is a bit more of a self centering action with them.

Andy, you may find this interesting, my experience with ER16 collets on a Unimat 3 fitted with new ER16 spindle.

I started with buying a backplate and ER16 chuck from ARC, the backplate was rubbish, bored and threaded grossly out of true. I started to make my own but as it has to be done on the Unimat itself for concentricity I found that doing it from steel was really beyond the capability of the machine and I felt that aluminium wouldn't be robust enough. (Mind you now I've made a tangential toolholder it might be different.) After having a few tries at making a screw-on one piece chuck (because I don't have a topslide for the Unimat) that were way out of true, I decided on the new spindle approach. As you'll see in my previous post, the spindle taper is pretty good but I found a big difference between nuts - as I've somehow accumulated 5 of them I was able to select one that is probably acceptable.

I probably also need to make sure I'm tightening the nut enough.

Have you spoken to ARC, before airing ‘dirty washing’ on a public forum? Might get a better response if that were done first.

He possibly or probably did. We have sold 100s of such backplates, and continue to do so.

Every batch is consistant, except for drilling of fixing holes in certain cases, but not proved to be a big issue. The final turning of registers is left to the machine operator, on his machine. It is difficult to say or prove clearly if the backplate is rubbish. All i know is this: Out of every 100, we get three to four complaints. The rest either seem to be usable for the user or if they have a complaint, it is something which they have failed to raise with us.

If the feeling of complaint is strong, we will just refund and move on, and leave it to the machine operator to get on to finding their own solution.

Ketan at ARC

Yes, I mounted the plate on the lathe, switched it on, and it wobbled like a swash plate. The threaded hole was clearly at an angle to the back of the plate.

I contacted Arc and they instantly agreed to a refund - I have always found them to give excellent customer service for the extremely small number of defective items I've got from them. In fact this is the only one I can remember.

The problem is likely to be that the nut is only done up 'firm finger tight'.

Even ER16 needs to be done up a good solid spanner tight. Also check the collet is clicked into the nut properly. The collet can't engage the nut properly once constrained by the holder so it needs to be fitted to the nut before inserting the collet into the holder..

Neil

JH,

My post wax for the OP, not yours which I did not realise, at the time, wax another complaint.

As I see it, if the backplate was bored and threaded off line, either the register fitted or did not. In which case threading on backwards and recutting the register would have likely been my first move (if appropriate), then facing the backplate afterwards - all assuming sufficient available thickness. Otherwise, simply back to the supplier. I have found that most suppliers are very, very good in that respect (banggood being the main exception, of course!).

I’ve had minor problems with Warco and Chronos, before now, and been sorted immediately. Chester, not quite so straightforward but sorted. Banggood - an utter waste of space, with no decent customer service at all, which is why I say you take a chance with them, so only buy if you can afford to throw it away if complete rubbish.

I have pondered during a job ER collet variance in runout when tightening. What I found is not to easy to put in words, but here goes..

The nut thread obviously has some play ( very small on a decent chuck, but must still have some play/clearance!)  when fingered onto the collet body thread, and when tightened up against a collet's top taper, the two threads find a mating medium. I found this medium to vary measurably with each tightening. As a result, while the nut is being tightened, it will pull up against the body thread on the side that the tightening torque is applied - ie, you grab the spanner and pull on the nut, pulling it over in that applied force direction. Since the nut moves ever so lightly in that direction, it's outer collar taper impinges more on one side of the collet than the other, closing that side more initially. This moves the held cutter over a fraction ( 0.005 to 0.008mm in my case). Even when fully tightened, the cutter is not centred properly. This is repeatable, and the rate of applied spanner force easily varies the runout from 0.005, all the way to even 0.01mm.

So, I tried using two spanners, 180deg opposed, trying to apply the same force to each spanner, and what do you know! First attempt gave 0.002mm, second 0.0025, third 0.0017.

It seems the trick is to not pull the nut to one side when tightening, and I get good results every time with my method.

However, it is not easy to do mounted in the machine - My tests were with the collet chuck firmly secured on a vise with Al jaws. Since doing up collets normally requires a spanner holding the chuck body, and another fastening the nut, I find myself short of an arm..

Hope my description makes sense.

Any bright ideas as to a spanner/jig/mechanism to hold the chuck and fasten the nut with a double ended spanner?

edit - 'than', not 'then'....

Edited By Joseph Noci 1 on 09/12/2018 11:19:21

NDIY, I'm afraid that if I buy a product with an egregious fault I'm not going to mess around trying to fix it because if I can't then I've invalidated the implied warranty. And recutting the register would have left it oversize so it wouldn't register any more anyway!

Joseph, a very interesting observation! I will do some experiments.

Joseph,

This is just to add to your observation...

Certain clockmakers/watchmakers who we serve as customers have the SIEG C0 which we used to sell. They do this work for a living, as their profession. They would totally overhaul the machine to meet their specific needs... outside the norm of general hobby use, as the accuracy is not designed for use by a watch/clockmaker.

These customers set up their machines for specific jobs.. permanently. They would tell me (they because I heard this from at least three different customers from their profession), that they would only be satisfied with the backplate and ER lathe collet chuck assembly, after they got the finest level of accuracy out of it. To do this, after they got the maximum level of accuracy as it stood by tightening the nut/collet assembly, they would proceed to measure the runout all the way around, marking the points of deviation on the backplate, and introducing bits of paper in such areas, 'as shims' in between the backplate and the chuck, to improve the accuracy further. this works well for them.

This is all provided the backplate is correctly threaded in the first place.

Ketan at ARC.

Edited By Ketan Swali on 09/12/2018 11:45:18

Qualifying phrases - “if appropriate”. ‘Asuming adequate thickness”. “Otherwise simply back to the supplier”

So, clearly back to the supplier, for either a refund or replacement, was the obvious outcome (you would have made one already, if that was possible and lower cost without time constraints?).

I have fixed several electrinic items (dry joints, loose wires, etc) over the years - after consulting with the suppliers before checking/ascertaining the underlying reason for the symptomatic failure. Often, but not always, cheaper and easier than returning goods for minor faults.

A smidgen of oil helps on the tapered surfaces too, as I think there must be a tendency for the collet to twist as it's tightened.

Martin.