Hitachi HT20 loosing thread lead after motor rebuild

[VTM]

So recently we had the spindle motor rebuilt on our old Hitachi Seiki CNC Lathe. Needed new bearings and what not. It's nothing spectacular, 1500 rpm electric motor. After rebuild sounds good, runs good, brakes fine. So now we are running a program we've ran many times. Face & turn, Thread , Finish pass on the O.D. to clean the burr. A couple thread passes again to make a good clean no burr part. So the Issue is on the second thread pass of the program the machine does not hold the same thread lead anymore so the tool wipes out the thread the second time around? Even at setup before I could cut the thread, measure, make an offset, re-cut and the machine would hold the thread lead. Not anymore. Any Ideas what would cause it? Wiring wrong? or?

 

[greggv]

You'ld probably want to look at the encoder drive for the spindle on your machine. Anyhow, that's where I'd start. A slipping, loose belt maybe?

 

[VTM]

Hmm, Yes. Good place to start. We did have to remove the encoder belt when we pulled the motor. And the belt is not in very good shape. I will take a closer look at that. Thx for pointing me in that direction.