ovality

The centre of the bores???

I think you mean the bores are out of round or measure oval.

Lots of things could cause that.

1. How old is the machine?

2. How far from the spindle are you working?

3. Do you stop the spindle to retract the tool?

In my past, I've had to put steady rests on the end of boring bars to keep them from drooping and making the holes 'out of round'.

First thing I would do is measure the out of round condition, where is the part not meeting the spec.? It it at 3 o'clock, or 6 o'clock?

I'll bet your getting droop from the tool and your out of round is between 12 o'clock and 6 o'clock on the part.

Check and let us know.

Laby