We are trying to cut rings from 4.5mm ABS sheet. The rings are 106mm0D x 99mmID, inside that we are trying to cut another ring 70mmODx62ID. We are ending up with shattering on the edge of the material.

We are cutting from the inside (smallest) ring out to the biggest ring. We have a vacuum bed.

Can anybody suggest what spindle speed and travel speed we would be best using. Also the best router bit for the job.