A few days back I was checking the run-out on my Red lathe.
The spindle, with it's front bearing nipped up to a point where the drag was noticeable but not too tight, showed aprox 0.001" on the clock. Also the same on the outside edge of the three jaw chuck.
"quite good". Pats oneself on the back (spends next five minutes trying to get the muscles back in place).
But when I chucked up a piece of ground round stock, there run-out went up to around 0.0025".
I know that three jaw chucks are prone to this, and when you think of the way the scroll works, it is no wonder.
Now, the usual method of getting concentricity is to swap to a four jaw and adjust it for zero run out. But this is a bit of a drag.
I was watching Stefan Gotteswinter's channel and he seems to get by very well by having allowed a slightly oversize fit on his back plate to chuck mounting and using this to tap the chuck into line.
He just slightly slackens of the three chuck holding screws and used a copper drift to gently knock the chuck until the clock shows zero.
This seems much preferable to swapping chucks.
Does anyone here use this method ?
Dave.