Long story, short - I blew my spindle controller on the Sieg SX2.7 a second time (the first was under warranty and within 30 minutes of powering on my machine from delivery)... this time, the machine is most certainly not under warranty. I've tried repairing the spindle controller board but I think I've a dodgy hall position sensor and that blew the board up quite spectacularly a second time. Enough is enough, and it's cheaper to replace the motor and controller card with a Chinese servo and controller. So, that's this weeks step into the unknown. And servos are pretty much an unknown to me. So, help!

I've got a Chinese servo (this one: https://www.ebay.co.uk/itm/112227829185) that's slightly larger than the original BLDC motor. Finally managed to nibble a 10mm Ali plate to mount the motor and get it belt-coupled with the spindle. There's a knocking noise I need to bottom out but that's a different story (I think that's the spindle). I've managed to operate the spindle in a commissioning mode with the servo in speed mode and that looks to be the kind of set-up that's appropriate for a spindle. I'll have to check my pulley calls as well - looks to be somewhat faster than the old BLDC spindle though I thought I'd calculated the pulleys to get the same tool rpm. Low RPM is torquey as a very torquey thing - certainly I could hold the BLDC stalled at 40rpm, the servo is having none of that.

Tomorrow I plan to start stripping down my controller box to support the servo signalling. I've got a 400 page Chinglish manual... looks comprehensive, but it's a right bugger to read, and certainly not something you can casually browse.

I believe (99% confident) that it supports Step/Dir control and I'm using UCCNC - which also supports this. So, plan 1 is to remove the analogue drive and M3/M4 relay wires, and instead wire a couple of TTL->RS485 adapters off the back of the UC300ETH controller to generate differential step/dir signals into the servo controller. If used in step/dir mode is this a positional control mode in servo-speak?, or should the servo be configured for speed mode still? Is there a practical difference?

But, what to do with an Alarm signal from the servo? I expect that if I'm spinning this quickly that there's going to be a good rate of step pulses, and if the cutter engages with a block of steel I could expect the servo to momentarily loose speed/position (but I guess the nature of a servo is that the position will be recovered?) There's an alarm output from the controller, need this be feed back into UCCNC in someway, or into the E-stop circuit? Can I expect sporadic alarms when the spindle cutter engages the workpiece? Should I simply ignore the wiring to the Alarm output?

The servo came supplied with a 3m power and control cable. The power cable is crimped fork terminals to wire to the controller, so I'm fairly relaxed about shortening this according to the final installation on (in?) the mill. The encoder cable, however, is a multiway plug on one end and a 15-w sub-d type on the other. Is there merit in shortening this cable or is it simply not necessary (I might be able to stow this inside the column of the mill).

I guess I'm hoping that someone can spell out any gotchas before I make a pigs ear of the integration into UCCNC. Like I say, servos are a whole new game for me.