So far I have added the z axis ballscrew on the side of the mill, however I have noticed an irregular movement. It seems that when the machine is moving down it applies pressure to the left, causing a slight tilt and the opposite happens when moving up. I know this can be corrected by tightening the shim between the ways. I was thinking of cutting a slot between the ways but I am a little concerned about causing stress fractures or cracking the casting with use. I think attaching it this way would not cause this irregular tilt . Any thoughts on this?