My QSM gearbox and motor do heat up under prolonged use but not so much as to cause me concern. I only ever use the machine in horizontal mode and I wonder whether you are running yours with the spindle vertical which might well make a difference.
I think the motor is continuous rated but perhaps not for the extended running that CNC may involve.
I have the paperwork that came with it and will check to see if anything is said about overheating.
See also:
https://www.model-engineer.co.uk/forums/postings.asp?th=142863
Edited By ega on 21/07/2019 17:30:19