Now that replies are possible :-

m_c The chuck as far as I can tell is a 4 jaw and hopefully independant jaws.(edit K12-100 4 jaw is self-centreing - meh).



My comment (sent as a PM) is that you should remove the chuck and measure run-out on the face and periphery of the back plate. If this is within limits then you should be able to set up the workpiece in a 4jaw chuck using a dti (plenty of vids on Youtube).

Run-out on the driving pulley unless massive is inconsequential.

Hope this helps,

Rob