Problem- partner 1 z axis drifting , encoder???

[fcycles]

Has anyone encountered this problem? Out of the blue while face milling a part the z axis started slowly diving down while the readout still shows the same position. I pulled the belt cover off to watch it as it runs , the servo is slowly pulsing back and forth very slightly and gradually starts diving the z down. Does This sound like an encoder issue? Or maybe servo brake? I pulled apart the servo and cleaned up the commutator and brushes - all looked good. But it didnt help. If the encoder was going out wouldn't the positioning readout shows changes? I appreciate anyones input
Thanks!

[jpawelk]

It sounds like the encoder is failing. Make certain that the encoder itself is connected tightly to the end shaft of the motor. It may also be the encoder cable as well. If the encoder is not giving feedback to the control, the axis can move and the control will not show the movement.

[fcycles]

I thought maybe that was the problem too , buuut Im an idiot , after i cleaned the tach up again with scotch brite it quit pulsing but i still had the same problem when ide face the material , turned out to be something in the aluminum that was very hard! It was starting a chatter and making it hog into it. Never ran into this at this extreme before, it was like they threw nuggets of carbide into the alumnium plate when they made it. Wont be buying there anymore!