Decided today to pull the chuck off and make sure there was nothing between the rear face and the spindle front face. As a base line I set up the dial indicator and turned the chuck by hand. Runout is 12 thou, that seems way too much to me?
Then locked the headstock gears and removed the chuck.
There was some dents and burrs on the rear of the chuck so I cleaned those off with an oil stone. The spindle face looked nice as did its thread.
However, the same could not be said for the thread inside the chuck. A bit scary actually. There were burs impacted into the thread the whole way down along with some bad damage (missing material) in the middle of the thread run.
I am guessing this is what happens when someone changes the chuck and does not clean out swathe first.
See photos.
Then remounted the chuck and retested with the dial indicator. Runout was identical at 12 thou.
I then put the alloy bar back in and decided (without much optimism) to try and turn the far end and measure the difference to the chuck end to establish how far skewed the headstock is. As predicted, the alloy bar is too thin and it chattered badly. Sigh.
I will have to come up with a way to sight the headstock to the bed. I am tending to think I will use the 11" alloy bar and align to the centre bore of
it with the live centre in the tailstock. This should get me pretty close, then using a fresh bar, repeat the process and fine tune.
Another option would be to put a small drill through say a 3" long bar in the chuck and then bore sight to the live centre in the tailstock.