I just have the regular screws on a Sherline Mill. I tightened the nuts to about .002-.004" endplay no problems and with EMC (cnc) compensate for backlash with nut mid length of leadscrew down to 0.001" no problem
Trouble is the screws are small and stretch and compress a little so as nut is at far end of leadscrew it has more endplay and when nut is near end it has less endplay.
Even if ballscrew and nut had zero backlash the ballscrew itself stretches and compresses. On a CNC with closed loop feedback, it does not count turns of the screw but movement on a linear glass scale showing actual movement.
On an old Prototrak mill with Trav-A-Dial encoders there is a steel wheel with fine teeth in contact with the side of the mill table. If a chip get stuck on encoder wheel computer says table not moving and gives it full power til it does move. I have seen the table jump an inch when closed loop feedback not working. With open loop cnc you are counting turns of a screw. Even a ballscrew with no endplay will not tell you if 10 turns is giving 1" exactly everywhere on the leadscrew. Old machines often have leadscrew pitch variations.
Sorry I am not offering any solutions.  |