A CNC milling machine with FANUC OM CNC controller, the finished products dimensions are all relatively right, but the exact dimensions of X direction are all has 10mm error, this should be the full pitch offset error(Ball screw pitch is 10mm), due to the reference point offset.

For most CNC controllers, normally the reference point will be set at “zero pulse” of the first programmer after the decelerate block, if the programmer happen to be close to the “zero pulse” while the reference decelerate block is releasing, the reference position could be has one pitch error due to the random error of the  decelerate switch action, this problem is more likely happen if the machine is using small pitch ball screw.

Solution for such problem is re-adjust the position of the reference decelerate block, to make it about half pitch away from the “zero pulse”, problem solved。