Strange surface pattern in x axis only?

Hi not sure where to post this,

I am experiencing a strange pattern when cutting only in the x axis direction, up/down milling doesn't matter.(see attached photos)

The strange marks happen to be ~5mm intervals which happens to be the same pitch as my ballscrew...?

I am using Linuxcnc + dmm servos.

I have tried leaving the end bearing loose and loosing the nut attachment so it can move in case of any alignment error but made no difference.

Note the endmill im using is not in good shape and is chipped but is no different with a brand new. Despite the avg finish it is very smooth.

Any help would be great

Ritzy

Bent ball screw maybe?

possibly a bent ballscrew as mentioned or the machined end for the bearing is off center