I have the same problem with mine. Its a Hm45 and I use the quil for Z.
I changed the motor on top to a 2HP 3 phase capable of running upto 3800 RPM. I even tried some really expensive 3 flute tooling and index cutters in it.
Ive cut 7075 and 6065 at different speeds and cut rates but dont seem to have a lot of luck. The surface finish is very poor when feeding or when plunging. The finish when fly cutting is perfect....
I couldnt really messure any major backlash coming from the bed but the fact that the fly cutting was perfect but vibrating everywhere else leads me to believe that the quil is slopping about. Ive replaced all the bearings in it and put rubber mounts under the motor. Ive checked the quil for runout and its 0.01 +- |