Need Help!- Bridgeport xv710 Stop Postion

[castle machine]

hardinge bridgport xv710. Keep losing spindle stop position. Spindle stopping at random positions, has anybody had this problem before?

[ppascuzzi]

Both the Siemens and the Fanuc versions used an encoder mounted on the motor for positioning, they also used a prox sensor that looks for a bolt on the spindle. A bad prox sensor would more likely cause no stopping at all. Given that it is a "random" stopping check 1) belts and pulleys to make sure nothing is slipping 2) coupling of encoder to motor to make sure nothing is slipping 3) encoder itself maybe bad (sometimes the disk breaks free of the shaft and this allows it to move some, it it is only slightly free it may only be noticable when positioning)