Z axis drop at startup!!!!

Fired up the 'ol VF2('04 machine) this AM. Start to home and Z axis drops to about 10" above the table, stops, and then drops all the way down. The sphincter activated Estop would have come in handy. Nothing damaged, thank the Lord. The motor brake obviously did not engage. WTH? Alarm was Z axis fault. But why didn't the break catch it? It would have been ugly if the Y axis wasn't all the way home. Called the local Haas techs and they had no clue why it did it also. The break will release when the Z axis motor has power. And the the opposite if the Z axis motor loses power, break will engage. This happen to any of you guys? The machine is up and running, but I still have the willies knowing it could happen again(maybe during a program?!?!?!) Ghost in the machine?

Way I understand it...that brake is part of the motor. It is supposed to fail safe. Some sort of magnetic arrangement.

Sounds to me like your brake is broke.

Check you don't have a chafed wire, you could block the head and pull the motor...check it out. Remove replace is where I'd head. Too dangerous not to, I don't know about you but I have important parts of my anatomy in my machine at times

I too would start looking for a rubbed wire, probably the one to the motor or encoder. The brake should be energized to release so a broken wire there would keep it locked. I suppose the drive could of gone bad but seems like a weird way to go all of a sudden.

JP

z axis break

Then the z axis break gets 24Vs from the I/O PCB the break is off. When it looses that voltage the break is on. Some how your I/O PCB keep sending voltage to the break. The relay on the PCB may have stuck open.

I think the counter balance for the headstock may need a bit of nitrogen, there should be a gauge around the left side, if I remember right it has to have 800psi when the head is up. worth a check.

I don't think the '04 has a counterbalance. Mine doesn't, just a bigger Z motor.

Did we find a solution?

Workin' on it