[CMM2388]

I am currently working on a retrofitted Devlieg HBM with a Fanuc 11M control. The x-axis is driven by a ball screw coupled by a drive belt to an older 30 Series Fanuc Red Cap. When moving incrementally in .001 increments the table will move .004 on the first move or when changing directions. If I continue in the same direction it moves in perfect .001 increments. I am measuring using a dial indicator on the base touching the side of the saddle. The .004 increment is not picked up by the drive. It doesn't try to correct and is being read as a .001 move. There is no backlash programmed into the control. Is it possible that the magnet on the servo is wearing out and the brake cannot stop the ballscrew fast enough when changing directions? Is there a simpler answer?

Thanks!
Ben

[underthetire]

Sure sounds like too much backlash comp (p1851). No, they don't use brakes for reversal, and red cap is an AC motor.