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Haas TM 1 spindle drive belt issue

gear cutter

Cast Iron
Oct 16, 2010
2009 Haas TM 1 milling machine. We have just replaced the spindle drive belt and the motor isolators on the machine. The motor was raised up and all the surfaces were cleaned including the two pulleys, The pulleys do not show much wear, no grooving on the teeth from belt wear. The problem we are having is the belt will not track, it drops to the bottom of the motor pulley until it makes contact with the bottom flange of the pulley. It does this during CW and CCW rotation. The original belt tracked towards the top of the pulleys, but did not make contact with the top flange of the motor pulley. There is no end play in the spindle or the motor shaft. Is there something we should do to align the pulleys to correct this? Any help would be appreciated.
No shims. We were very careful about that. The original isolators were really deteriorated dry and crumbly. We raised the motor straight up enough to be able to clean and see what we were doing.
A buddy of mine did his mini mill last year and had the identical problem. It also had a wah-wah-wah spindle speed oscillation issue after installation. He figured it was due to worn pulleys.

He just told me it wasn't hard against the bottom of the pulley. It drifted that way. He ran it. The oscillation went away. He doesn't know if the pulley tracking solved itself or not.
My understanding is this was common and a no issue.

I’ve had 3 haas mills now (x2 tm, 1vf) and they all do this with no issues at all. (Tracks one way and lightly touched a flange)