I assume you had to remove metal because the jaw was outboard of the other two. The screws won't be able to hold the jaw without a shim of 0.3mm in place. The easiest source of shim material for this type of job is to sacrifice a feeler gauge. You will then have a source of various thickness steel to get your jaws fairly good. Three jaw chucks rarely run better then about 0.08mm tir.

Mary?

Tim

Rich, This sounds like a chuck with I assume soft jaws?

I found with my Tudor style chuck you need to have both the tee nut and the top jaw matching the position on the body. have you checked the body runs true first?

If they are removable soft jaws on the chuck they should be turned in-situ to reduce run-out. A special plate should be used while machining the jaws so they are clamped in the normal working position. (do a Google/Youtube search for examples).

Paul.

Richard thanks for your reply. I understood what you had discovered from your earlier posting. What I was trying to establish was what happens when you put a piece of say 3/4 or 1 inch bar in the chuck and turn down the OD by say a 1/4 of an inch (6mm). Do you get a round bar of common size along its length, and which is not tapered or eccentric?

He is going to get eccentricity between the gripped section in the .3mm offset jaw and the turned section.

Taper along the length of the turned section has nowt to do with chuck jaws and all to do with matters like headstock spindle alignment and bed levelness straightness.

Edited By Hopper on 04/10/2019 06:17:38

I assume that you are checking the concentricity, or lack of it, whilst holding a bar in the chuck, not when the jaws are loose? ( Check that your "test bar" is round and not oval or trilobular )

Is your GH1440 new, and in warranty?

If so, and it has been like this since new, I would not tamper with it but complain to Roger Warren at Warco, asking for a replacement chuck.

The serial numbers on the jaws do match the serial number on the chuck? i e You haven't got an odd jaw from another chuck by mistake?

I have a small 3 jaw where one jaw has a serial number differing from the others, BUT it does run about as true as on can expect for a 3 jaw.

I would not expect absolute concentricity, 0.1 mm would be quite acceptable. I have only ever come across one 3 jaw chuck that did not run out. The worst, a badly worn one had a 1 mm run out!

If it is a sudden new problem, on a machine, out of warranty, you need to find out what causes it. The only way to find the cause and effect a cure, is to carry out a series of checks, starting with the simplest, and moving through in a logical sequence.

Does the run out vary each time, or is it consistent?

Are you certain that the register faces for the chuck, on mandrel and chuck, are clean and undamaged ?

Are the backs of the jaws clean and undamaged?

Is the scroll clean and undamaged?

An old tooth brush held in one of the slots, while the chuck key rotates it, is a handy way of cleaning the scroll. Will take a few minutes to run right through the scroll, but could be time well spent.

Is the back of each jaw clean, and free of dirt? Ditto for the slots for the jaws, in the chuck body.

One of my friends cleans his chuck jaws with a small wire brush every time before fitting into the chuck.

Since this problem seems only to affect one jaw, the jaws must be in the correct slots or the run out would be enormous, (by the pitch of the scroll ).

If all else fails, then, as Paul Lousick says, fit a spider and set up to grind the jaws. After all, on the face of it, you have only 0.3mm of metal to remove from one jaw. (Although once set up, I would go the extra few microns to ensure that all three jaws clean up.

Do tell us what you find. You could help someone else, with a similar problem.

Howard

Richard,

It strikes me that you may need some physical help, as well as the sympathy of others on here.

Where are you located?

Maybe some one could visit and help you? Two heads and all that.

Howard

Here's a picture of a slot and tenon reversible chuck of the type that the op has:https://www.ebay.co.uk/itm/160-mm-3-Jaw-Lathe-Chuck-with-Direct-Mount-D1-3-Camlock-Ref-K11160AD3/372368686702?epid=26021416087&hash=item56b2e73e6e:g:rX4AAOSw0eBbSd9T

Edited By old mart on 04/10/2019 18:36:45