What hasn't been mentioned, is the spindle drive fuse was blown (there's a concurrent thread over on the Denford forums).

I've just had a look at the wiring diagram, and the fuse should be 6.3A.

If the motor stutters/stalls briefly when running, it's could be either the SCRs on the drive are failing (they tend to fail short circuit under certain loads, which causes the stuttering/stalling), or the motor is either shorting out internally, or the brushes are not making good contact (which again gives the stuttering/stalling).

The issue with the spindle motor, is due to it having a tacho fitted, beyond removing the brushes, they are a nightmare to dismantle and clean.

I personally removed the DC motor and sprint drive from mine, and retrofitted it with a servo motor and drive.