Many thanks for taking the time to reply. I've been using G96 Feed per Revolution .xml is attached, appreciate if you could comment on it. The other problem you may be able to advise on is spindle settings. I've tried many different settings to achieve the full 10 volt output to inverter, the problem being that this would drop back about 0.5 volts during rapid moves of X or Z axis and therefore spindle speed would also drop slightly. The settings here work but I also had to alter P.I.D. settings a fair bit as with the default settings it was taking about 40 seconds to get the programmed speed ! There is now some overshoot for a few seconds especially upon increasing spindle speed. Threading seems to work ok though. Many thanks, Nick