I am having a strange problem in my carve. I have done 5 of these with perfect results. On the 6th carve the machine cut deeper lines across the carving in the middle of the carve but not at the start or finish. I cleaned the y axis bearings and rails. The bearings seem fine. I checked the y axis readings and there is some variance between extreme up and down position. It seems to change depending on how much pressure is put on the up and down stop when manipulating. Any thoughts, i do not have a z pack to replace and have 15 more of these to do.