Hi Fizzy, presume its a Harrison L5? however which spindle nose does it have? Do you perchance have a similar chuck and have mixed up the jaws, they are usually serial numbered as well as 1.2.3.

For any fix you need to work through any elements where an error could be from the spindle nose to the backplate register and so forth to the chuck body etc

Hope this helps a little John

When you take out the chuck jaws to check the sequencing, look at the scroll and the jaw scroll segments to check there ain't a piece of swarf wedged in there.

Look at the front face of the chuck whilst running and see if there's any wobble.

Edited By Mick B1 on 24/09/2017 11:10:16

Don't bin it. The jaws can be trued up with a Dremel type tool held in the toolpost if a suitable "clover leaf" or packing pieces are used to spread the outer ends of the jaws while grinding is done.

Depends how accurate you need it to be. It's quite reasonable to expect a new 3-jaw to be concentric to a thou or two and some – even budget ones – can be better than that. Plus there's always the option to machine a set of soft jaws to achieve the same or better.

I think the OP's quite right to think something's more than usually out of line when a chuck that appears to be correctly fitted shows 10 thou eccentricity.

Tim Stevens has said it all really, but I will just add that the best concentricity on a 3 jaw when new will be within 2 to 3 thou, if you get one that is spot on, it will be by good luck alone. If you turn all the faces of the component you are making, it will be concentric with the bed of the lathe, but not concentric with the bar left in the chuck, so your finished component will be unaffected by the inaccuracy of the chuck. This is why you should always use stock which is oversize in all dimensions. If you consider the way a scroll chuck works, any slight movement in the pivot of the scroll, or the recess it seats in will result in unequal torque on the jaws, and give rise to run out. As Tim says above, if the chuck has been over tightened, the scroll itself can be bruised and that will bring inaccuracy at certain diameters.. Grinding the jaws is not an answer, one of our biggest chuck makers (can't remember which, but someone will) used to offer a recon service, and gave it up! The most accurate chuck you have is a 4 jaw independent.

Yes, I got one o' them, too, leastways on the main jaws when new. Still OK to about a thou an' a bit after two years' abuse…