I've not got much time just now to give too much of an in depth reply, but the revving up then settling down isn't normal.

As has been mentioned on the Denford forum, it could be a tacho fault.
The 60-100revs does sound correct for 200mV, given it's a 0-10V signal, so 200mV should give around 2% of max spindle speed.

If changing the jumper to ignore the tacho input doesn't work, I'd measure the voltage across the 54/55 wires when you power the machine up. IIRC the spindle drive shouldn't even be powered until the controller is fully booted, and the spindle go relay is activated.

I seem to remember there being some machine settings within VR Milling. Is there any relating to the spindle?
If the analogue output isn't working, then it somewhat restricts your options for controlling the spindle from the software.


I fitted a Kinco servo motor and drive at the time, which cost quite a bit. If I was doing it now, I'd look at Lichuan servos, but it involves making a complete new motor mount. I do have a thread on here about my Triac retrofit, and I think it includes some details for fitting the servo.