12" between centers would probably depend more on how well your
tailstock center is aligned with your headstock and how accurate your
centers are. You should be able to turn something between centers to
the accuracy of your spindle TIR which in the case of the Prazi should
be .0002".

Turning a 12 inch long shaft with 2 tenths taper on a small machine
is a pretty tough job. I highly doubt I could achieve this with my
myford or my rockwell. Especially if the shaft has a small diameter.

chuck