❓ Question — from a die-mould shop, Rajkot
Haas VF-2 (older Sigma-1 motors) trips SERVO OVERLOAD on Z during the first 30 minutes each morning, then runs fine all day. Do we need a new motor?
✅ Answer — JJ Automation Technical Team
Cold-only overload is a mechanical-drag signature, not a typical motor failure. Motors that are actually failing trip when HOT, not cold. Check:
- Way lube on Z — the #1 cause. Verify the lube pump cycles and oil actually reaches the Z ways/ball screw (crack a metering valve and look). Thickened lube in winter + vertical axis = high starting torque.
- Counterbalance — VF-2 uses a gas-charged counterbalance cylinder on Z. Low charge makes the motor lift the full head weight. Look for oil weep at the cylinder and listen for the head 'settling' at power-off.
- Load meter comparison — in the DGNOS/load screen, note Z load% cold vs warm at the same feed. Cold 150% falling to 60% warm confirms mechanics.
- Brake release — a lazy Z brake (sticky when cold) drags the motor. Feel the brake area for heat after a cold-run trip.
- If load is high cold AND hot → then suspect the ball screw bearings/preload, and only after that the motor/amplifier. Swap the Z amplifier with X to test the electronics cheaply.
Reply below with your load-meter readings cold vs warm and machine year — brake and counterbalance designs changed across generations.
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