Servo as a spindle motor replacement - what to look out for?

[JAZZCNC]

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?

I believe you can only use Position mode with Step/Dir signals. You need Analog to use Speed or Torque Modes.

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 fact UCCNC doesn't provide a Spindle or Servo Alarm input to connect upto means your only safe option is to tap into the E-stop.
This will need to be done because when the Servo faults it doesn't just throw an alarm to say it's lost position, it cuts the outptuts and stops the Servo.
You will also need some way to Reset the Fault as well. This can be by powering down the drive or pulsing one of the inputs and configuring it to Reset the drive.

I doubt you'll have any problems because the default Peak torque is 200% and rated for 8s so you'll have 5Nm for 8's before it faults, it's also programable in the drive so you can increase to 300% and set the time current fault overload time to 80s if needed. But I can smell the smoke already if you did that...Lol

This should give you planty of torque when entering the material, there are also over options in the drive you can play with to boost torque if required. Provided you can get past the Chinglish.

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).

They are easy enough to shorten but I would just leave it if it's not causing you any grief.