Thanks Clive, that's very interesting and encouraging. To add a little more to the picture, I run a workshop with all manual machines but for the one CNC mill I mentioned earlier. I don't have three phase to the building so I run of a rotary converter, which does the job pretty well. My CNC mill is all powered by servos and 240v input AC drivers, with the exception of the main spindle motor which is three phase. I mention all this because looking on the Chinese sites, it seems that the biggest driver I can get with a 240v input is around 3.5 kW. The spindle runs via a variable drive belt system which for the most part does its job well, but I would like to remove it completely and replace it with a toothed belt and suitable gear ratio. Looking at the info you gave me it would seem that torque from a servo would be in my favour. Money aside, this seems too simple, are there any other issues. Again, thanks.