Originally Posted by
awerby
Is the problem happening on the roughing or the finishing pass? If it's on the roughing pass, think about leaving more of a finishing margin. If it's just on the finishing pass, your tool may be dull, or you're taking too much at once. You can always divide the finishing pass into two, taking half as deep a cut at a time. A down-cut tool will be less likely to chew up those top edges.
The sharp edges on that volute are going to be difficult no matter what you do. If nothing else works, leave them rounder and fatter than the final part, and finish them up by hand.