ER-32 collet chuck

[Allen Smithee]

A couple of weeks ago I bought one of these ER32 collet chucks which I thought in mounting directly on the spindle of the myford would probably be stiffer than the flange/backplate type:



When it arrived I tested it with a range of different size collets by clamping milling cutters in collets and clocking the run-out. I came to the conclusion that it was parallel to the spindle (to beyond what I can measure), but has a concentricity error of ~0.0025", which is a shame because I had hoped for better - but then it is a "budget" item. I've contatced the supplier and they are sending a second one (which is nice of them - no complaints) but the cynic in me feels unless I'm very lucky it will be much the same. I have a dividing head with a Myford spindle, and for anything *I* am likely to do this chuck will be more than accurate enough for that, but as it looks like I'll end up with two of them I was wondering...

As it's only two and a half thou there is more than enough material to re-cut the collet seat, so I'm strongly tempted to see if I can re-cut the taper in-situ (which should essentially guarantee it's concentric, obviously). Three approaches spring to mind, all using the taper of the existing bore to set the topslide angle:

1. Bore it with a tipped boring bar, making absolutely sure the tip height is as closely aligned with the spindle axis as I can achieve (I'm aware that taper-turning is the one case where very accurate tool height really matters). The only thing that might be a problem here would be if the part has been hardened (I'll test this with a file on the front face somewhere).

2. Similar to (1), but using a dremel as a toolpost grinder, looking to take (say) a quarter to half a thou cut per pass with the lathe turning at (say) 100rpm. I'm not really keen on grinding in the lathe, but this once I guess I can accept it and ensure the ways are all covered up.

3. Turn up a lap to mount in the tailstock, using blue and the current taper to ensure the angle is correct, and then try lapping it back to concetricity. This would be messy but more gentle than (1) or (2), but I've never heard of anyone using lapping to correct a concentricity error.

Does anyone have any thoughts/guidance/derisive-laughter to offer?

AS

[Roger B]

My first though, is the run out consistent when you remove and refit the chuck to the lathe and when you remove and refit the collets? If you mark the high spot with a maker pen or tape you may be able to determine where the problem lies. If the fit in the lathe spindle is not consistent re-cutting the taper will not help.

[fcheslop]

Hi ,its the same chuck I use on my Myford with the same problem
I re bored the the socket for the collets
To set up I simply fitted a collet to a bit of stock between centers and clocked in the compound slide .Then took a few thou cut and just tweaked the slide in using engineers blue on a collet.
I have found that you need to fully tighten the collet closer or it runs out by about a thou . I replaced the original nut with a bearing one from arc
My chuck machined very easily using a boring tool made from stubs or hss as its all I use
Im not a great fan of this chuck but now seem to be able to get within 1/2 a thou. The locating spigot is a little loose on my chuck or not a good as I would like at least 
Guess thats what we get for buying cheapo gear
For better accuracy I make my own 2 morse collets to go into the headstock mandrel a little limiting on size though but good enough for a my needs
cheers
frazer

[Jasonb]

You might want to have a look at Bogs post about making one of these collet chucks, the boring of the ER taper will apply in both cases. If you use a tipped tool then I would go with a $$GT one as the sharper tip is better for taking small cuts.

http://www.modelenginemaker.com/index.php?topic=1411.0

[Allen Smithee]

My first though, is the run out consistent when you remove and refit the chuck to the lathe and when you remove and refit the collets? If you mark the high spot with a maker pen or tape you may be able to determine where the problem lies. If the fit in the lathe spindle is not consistent re-cutting the taper will not help.

Sorry, I should have mentioned that. Yes - I did just that and have satisfied myself that the run-out is all a concentricity error between the front-end machining (collet taper) and the back-end machining (spindle register)

AS

[Allen Smithee]

Frazer - many thanks for that. If it machined with HSS then I guess I can assume it's not hardened so I'll go for the boring option. It's got to be worth a try as I will have a spare one anyway.

I also found the register fit wasn't brilliant, but despite that it seems to mount consistently - the measured run-out was always the same and always in the same place in over a dozen remove/refits.

Many thanks for the info, chaps!

AS