This is an enclosed 2.2Kw water cooled motor.
This look like ABS plastic box.
I made a couple of hundred box from time to time maybe once every 2 months or so.
I have to do ramping machining because this material tend to melt and become very hard.
If I slow down the RPM, can't go as fast so keep RPM to 21000 and ramp, this takes a couple seconds more to machine but I have not had any melting since that
Use a 1/16 2 flutes carbide end mill, I have tried 1 flute and a 2 flutes zero helix but the best for me is the 2 fluted.
Have to use 1/16 because they're two cut out for DRO and corner have to be sharp and .031 radius is OK and accepted
Jeff