INTERMITTENT SPINDLE ORIENTATION PROBLEM

The machine Haas VF 4 built 6 1997

22 Hp hi torque, no rigid tapping, no vector drive (SHOT PIN machine)

The INTERMITTENT problem,

Some times when doing a tool change, the spindle will not orientate properly. It can be off a little 15 deg? or a lot 90+ deg. It will proceed to do a tool change putting whatever tool is being used away wrong and pick up the next tool wrong also. (the drive lugs not in the proper spots). Also it happens on all tool locations intermittently.

My current work around,

M5

G4 P500

M19

M0

M6T?

If necessary I spin the spindle by hand until it locks.(I can feel the shot pin dragging on the collar and firmly locking).

The shot pin seems to work as designed no air leaks, retracts properly.

The shot pin collar appears good, some wear, not what I would consider bad

I have watched the DISCRETE INPUT PAGE that shows the Spindle Lock changing from a 0 (UNLOCKED) to a 1 (locked)

After some experimentation with no air to the machine, I can push the shot pin in (to the large diameter of the collar NOT locked) and the Spindle Lock will switch to a 1(locked) even though the shot pin is not seated in the grove.

If the drive lugs are straight to the front of the machine, and I push ORIENT SPINDLE sometimes the shot pin will actuate but the spindle doesn't turn to the proper orientation.

Other notes,

The spindle drive was replaced 5 +years ago, after the repair it started taking longer to orient the spindle but still oriented correctly.

Recently we had the main board rebuilt (eeeeeeee displayed on screen), the problem didn't get worse or better after that.

Is it possible that the switch is out of adjustment?

Does anyone have any recommendations?

Thanks

Erich