Sherline's High Speed Air Engraving Head For CNC Mills In most machining conditions it is not necessary to achieve tool speeds faster than the 10,000 RPM that can be produced with the standard DC motor spindle with optional P/N 4335 high speed pulley set. However, for engraving and other applications where extremely small, pointed tools are used, higher speeds are required for good finishes and acceptable feed rates. This spindle is capable of speeds up to 54,000 RPM and will hold 1/8" diameter cutting tools in its collet spindle. Three carbide tools with various cutter face angles are provided with your engraving head along with 7 grinding tips.