Zirconia Marginal Chipping when milling

Our lab uses Sirona's inLab MCXL for milling, and have had some issues with milling zirconia crowns. We are having problems with marginal chipping during the milling process. When a prep doesn't allow much space for the margin thickness we usually bulk it out a bit, but that creates a lot of extra grinding time. But my question is would anyone know what might be causing the chipping of the margings when being milled? The machine is calibrated once a week, and we keep the burs fresh, but still...

September 26 at 8:09 am