Circle milling

[bq911]

Hello all,
I have a question about locational accuracy of a circle milled boss. We have an older Bridgeport Mill Slide with a Centurian 6 control. We clock in a piece of round stock, circle mill a diameter at the desired location. We then clock the machined diameter and the location is between .0035 to .004 off center. Any thoughts?
Thanks,
Bill q

[bq911]

P.S.
The machined boss is round within less than .0005.

[Superman]

The head is not perpendicular to the table ?

Try having the indicator set to about the same distace out as the cutter, or tramm head to be perpendicular.

Backlash in table leadscrews ?
Indicate an edge winding in one direction to clock zero, observe readout value. Go past, and wind back to clock zero.... you should have same readout value.