Had another look at the machine.

Spindle motor is driven by Mitsubishi VFD but not using variable speed as there is a continuously-variable pulley drive (plus back gear) on the mill. Still thinking about whether it's worth using electronic speed control as there's no tool changer so setting speed manually at the same time as manual tool change isn't a big deal. No big issue either way - it's only another cable.

Servo motors are badged Anilam (well, one of them has a barely-legible label). Brushed dc. Label has spec for tacho output but don't know if there is a resolver or encoder. I've seen an article about updating a similar system which used an encoder but I've no idea how standardised these systems are.

Need to update controller anyway but servo options are new dc drives (CNCdrive?) assuming that there are encoders fitted, costing around £300, or new ac servos plus drivers for around £750. Needs adaptor plate or similar to fit machine but all new technology, low technical risk, and if it all comes from SZGH, it's more-or-less pre-configured from the factory complete with cables.

To date, SZGH have been very quick with supplying manuals and quotation. Can't see from first look at manual if you can use limit switches as home switches but I can ask them. Only one upper limit and one lower limit switch input so all axes share these, which is why I'm not sure about home switches - there might be some other inputs for these but still decoding Chinglish for those...

It's not my machine or my money that's being spent although I would tend to favour the all-new setup. If it were my machine, I would probably spend a bit more time on investigation but this machine belongs to someone who wants to use it, not turn it into a project!