Good point, Mick. It runs smoothly with the disk removed, but the disk is heavy. If the shaft is bent, the disk will be running out of true, and its heavy weight would cause vibration, even if the disk is not damaged. This could be checked by the test I described in the balancing procedure: check whether the outside of the disk is running true. That is likely to be easier than checking whether the shaft runs true, and it tells you more: if the disk runs true, both it and the shaft are OK.
