I have been trying a 6mm single flute carbide bit @ 21000 RPM 400mm Feed and 2mm depth, but the subject always gets to hot see pic:-

Click image for larger version.  Name: first-cut-is-the-deepest.jpg  Views: 475  Size: 78.7 KB  ID: 12721

should i try faster feeds? slower spindle ? deeper cut ? or some form of coolant / lube ? to resolve the heat build up.

Thanks