Just to update. Cut a few models yesterday with a feedrate of 40mm/sec at 6mm DOC. The spindle was running a 6mm two fluted bit at 24,000rpm (flat out according to the dial). The cut was just as good when running at 20mm/sec. When I went above 40mm/sec there was like chatter marks on the cut edge. Is this due to the feed speed being too fast for the cutter speed or is it that the cutter is getting blunt. I have never seen this before