ER 32 Collet Chuck Problem

[Anzaniste]

I have just finished mounting a ER32 collet chuck on my Boxford lathe. The chuck has a 55.5mm recess in the back and I have turned a suitable spigot onto a commercially made backing plate that fits the Boxford nose piece. The spigot is a very nice fit and clocks zero TIR as I would hope it should. I was very disappointed after mounting the chuck to find that there is a .003" TIR when I clock on the internal taper of the chuck. This eccentricity is repeated when I put a piece of silver steel in the chuck.
This is no better than a  3 jaw chuck and I am pretty fed up.

I put the indicator on the face of the chuck and got about .002" swash, that surprised me as my machined back plate was spot on. I have checked for dirt and bruising of the mating surfaces and that does not appear to be the source of the inaccuracy

I have not checked out with the supplier of the chuck what it should achieve nor am I able to do so for a week or so 'cos I shall be away from home. I was expecting virtually zero TIR.

What collective experience is there on this forum with mounting a ER32 collet chuck on a back plate on a lathe. Am I expecting too much

[Bogstandard]

Just to let you know what to expect from these commercial items.

The supposedly 'accurate' 5C collet chucks I have fitted previously, and I have done a few. Every one had to have the internal nose taper reground to get them to within tolerance, which they say should be 0.001", my findings were well above that. By doing the grind myself, I can get that to well less than 0.0005", in fact I would expect 0, but a bit of dust on the collet can knock them out somewhat.

I have heard thru the grapevine that these bolt on ER jobbies are worse, hence, that is why I made my own.

It is just the law of averages on cheap tooling, that they aren't made to the same specs and quality control as expensive ones. If they didn't clean a tiny bit of swarf off the holding jig during manufacture, you will get a variation in their tolerances.

You might be lucky and get a replacement that is better, but on the other hand, you could find you end up worse off.

The chuck requires mounting onto it's backplate, then fitting to YOUR lathe, followed by truing up the taper. If you are lucky, and the ER chuck isn't fully hardened, you might get away with turning the taper true with a razor sharp cutting tool, rather than having to grind it.

I am sorry to say, that is the price you have to pay for precision.


Bogs

[andyf]

I had a similar experience with a cheap bolt-on ER25 chuck. It wasn't hardened, so I was able to bore it out. Don't take much off, because you don't want the collet sitting so far back in the chuck that the closing nut can't clamp it down on diameters at the minimum end of its range.

Andy

[Andrew_D]

Another thought that doesn't include messing with the collet taper...

We are dealing with ER32, so 3/4" is roughly the max diameter it's going to hold. Place a piece of 1" stock in your 3-jaw, turn it down to 0.750". Do not remove it from the chuck. This way, it is exactly concentric. Now using a 3/4" collet, clamp the ER-32 chuck to the 3/4" diameter piece you just made. Now you have two chucks (3-jaw and ER-32) joined by that piece of stock. Re-do the back of the ER-32 collet chuck. It should now be concentric with the collet taper on the front...I'd take extremely small cuts since there likely won't be a lot to remove anyway and you are dealing with massive overhang. Then make your backplate to fit the measurements of the "new" ER-32 collet chuck. I had to do something like this to a 3" 4-jaw I ordered from LMS...it just wouldn't quite fit on the backplate.

Another option is to use the same idea to make sure that the rear is square to the collet taper, then machine the spigot on the backplate undersize by 0.010" or so. This way you can "bump" to collet chuck into being concentric before tightening down the mounting bolts. Some variations on this have included using screws in from the side of the chuck bearing on the spigot to make the adjusting a little easier.

More things to think about.

Andrew

[DICKEYBIRD]

Another option is to use the same idea to make sure that the rear is square to the collet taper, then machine the spigot on the backplate undersize by 0.010" or so. This way you can "bump" to collet chuck into being concentric before tightening down the mounting bolts.

Yup, works a treat on mine!