Piece of crap mill, it was in the shop when I inherited it (high school metal shop) and never worked. Finally today I got the power hooked up to it (work order was in for over 2 years, I love my school districts idea of what is a priority, not me, but the school boards office needed new lights...) anyways When I got it running, low and behold I have over 30 thou backlash on the Y axis. Now I know that Microkinetics put their own ball screws and tapered roller bearings in the machine, and its not a normal backlash problem, the problem is this:
When you move the saddle towards the column (a round column mill drill for those that don't know, sucky I know) the outer roller bearing by the motor is tight to the housing but inside there is some room between the inner bearing and its race. When we reverse the direction the ball screw, bearing assembly moves outwards 30 thou before the bearing contacts and rides against its race. I have tried everything, made sure I wound the screw out so the inner bearing was tight to the race, then put on the pulley and lock nuts on, using a pipe wrench of all things to get the bearings preloaded as best I can. No difference the best I get is 30 thou, useless for cnc. I am going to talk to the manufacturer tomorrow but have found them to be useless in the past. Anyone know if anyone else uses a ball screw system like this and any ideas. All I can think of is the inner bearings rests on a turned shoulder pressed on and the outer bearing slides up to this shoulder but not far enough to contact the race. I will try shimming the races and see if that gets me anywhere. Anyone got any ideas?