Fadal EMC Spindle Speed Erratic

We have a Fadal EMC machine with rigid tapping and the Yaskawa 515 spindle motor controller. I think the motor is 5hp. It has the "88" controller if that sounds right. The spindle will sometimes speed up and slow down for no reason then shut itself off as if the emergency off button was pressed. Sometimes when commanded to change tools it will move the spindle around slowly like it is trying to orient itself then shut off. From looking around one thing that can cause this is the spindle encoder.

1) Are there instructions anywhere that explain how to clean or replace the spindle encoder? Looks like you have to work around the draw bar, possibly a lot of tension there. Where can we get an encoder cheap?

2) I've read some people replace the encoder with one that has a higher resolution. Are there any practical advantages/disadvantages to that? What settings do you have to change if you put a higher resolution encoder, for example the spindle motor controller settings?

3) The rigid tap has never worked correctly. It doesn't back out with the same pitch that it tapped with. How can that be fixed?

4) Can a 4th axis be added to this machine without too much trouble or expense? The build papers say that it is prewired for a fourth axis. I am no machinist but we could sure use a lathe. Is it possible to put a horizontal fourth axis, like a big drill chuck, that rotates slowly while the slide moves under the spindle to accomplish a crude lathe with a 6" or more horizontal working distance?


Thanks in advance.

-jm

Turns out the problem was a bad contactor connection. A screw terminal on one of the two contactors in the box attached to the spindle motor was loose and had overheated. The symptoms were just like a bad spindle encoder. If you have this problem be sure to check the screws on those contactor terminals for tightness. The loose location was melted but there is another set of contacts on that contactor that were not being used. I rewired to that set of contacts and it seems to be working fine now. That was the only problem we've had with the machine is 11 years of use.

-jm

jm thanks for the follow-up. It may help someone else in the future.