Lathe runout

You might want to try several different diameters of rod before you start grinding a jaw - if the same jaw looks out of whack on multiple diameters, grind it, but if the error is not in the jaws (but is in the scroll) "fixing" it for one diameter could make it worse for other diameters.

For the most part, if you want precision, don't use a 3 jaw chuck - use a 4 jaw chuck and a dial indicator.

L&S:

Your .002" is just fine. Consider that drill rod specs often exceed .002" and that you have spindle, chuck, and gauge runout combined. Add to that the small deviation from an indicator, as well as the tolerances therein. I use certified pin gauges, so that I at least know one part of my measurement is within a tolerance.

Regardless, there's nothing to fix. If a 3-jaw is running within .003" you're still doing just fine. The issue of runout only really matters when you have to re-chuck the work, particularly if you have to reverse it and you want to keep things concentric. Collets provide some solution, as can turning between centers. Even if your 3-jaw is visibly off, you can still turn perfectly round work, and as long as you leave the piece mounted in the chuck until finished, it will come out just as good as a "perfect" lathe.

I don't know if you've gone down the path of testing how perpindicular your cross slide moves, or if there's any twist or wear in the bed, providing a nice taper...

Sometimes you're better off _not_ knowing.

Is the chuck directly mounted or attached to a back plate. If attached to a backing plate, you can loosen the chuck from the plate and center up your chucked rod using a dial indicator. This may only help for the diameter of rod you set it up for if the scroll is unevenly worn. Your chuck should also have one of the three tightening pinions marks. For maximium accuracy, use the marked pinion to do the tightening.

And, just in case you don't think of this on your own: Mark the part and the chuck before you remove it so you can re-chuck it with the same relative rotational orientation.

Sometimes the master pinion is determined by the chuck manufacturer during the final inspection process and an inspection report packed with a new chuck will tell you it's location or number.

Once you find the master pinion, try to always use it when tightening the chuck on critical work, particularly when re-chucking as described above.

Jeff

I'd take off the chuck - unscrew it from the spindle - and clean the threads on both sides.

Often, metal inside the chuck will lodge in a thread when spinning one on and a good square seat is just not possible.

When I got my lathe from Dad it was that way - it was shipped to his new place and was placed in a room - in boxes and frame. He set it up and just never got back to it. When I got it home, I noticed the same thing - hum - to much runout. Take off the chuck - and yes there was a layer of brass near the end - perfect lever arm.

Once cleaned and I mean the chuck also - it seated against the back wall and was true.

Martin