Spindle Sync Problem on SQT15MS

[mbpp]

I'm machining the first side of a part in the main spindle, then moving up the sub spindle gripping the part, synchronizing the spindles (M511), parting off , moving sub spindle back home, machining second side and dropping it into parts catcher.
The problem is that the part has some slight marks from the sub spindle jaws. Not excessive gripping marks but marks that suggest the spindles are not synchronised properly. As if it is spinning in the sub spindle slightly during parting off.
Am I missing an M-code or anything ? I just use M511 . Any help would be appreciated.

[onthebumper]

Take a look at the spindle loads when they are synchronized. if the spindles are fighting once synchronized you will see one or both of them with a higher then normal load. Usually the load will continue to increase as they are fighting each other. If the loads are normal then maybe check the chuck pressure? Maybe some other application issue?

[yepingapple]

Please check the concentric of the two spindle !