HAAS® Alarm Z- — Z-AXIS NEGATIVE OVERTRAVEL
Part of: our HAAS® alarm reference · covering 60 of the most common alarms.
What it means
Z tried to move further down than it's allowed to. The most common overtravel alarm in real shops — almost always a tool length offset (H value) wrong for the tool actually in the spindle.
Common causes
- Tool length offset H value wrong — the control thinks the tool is longer/shorter than it is
- Wrong G54 work offset Z value
- G43 missing from the program (no tool length applied)
- Probe touched a surface at unexpected Z
What to check first
- Confirm the tool in the spindle matches the tool number called
- Confirm the H offset for that tool number is correct
- Confirm the G54 (or active offset) Z value matches the workpiece top
- Always check H values after a tool change before running
Prevention
Most overtravel alarms are programming or setup issues, not machine faults. Build a habit of always confirming your tool length offsets and active work offset before pressing cycle start — especially after a tool change or a fixture swap. On 5-axis machines, simulate moves before running them; trunnion clearances are easy to misjudge.
If you’re still stuck
If you’ve worked through the checks above and the alarm hasn’t cleared — or if it cleared and came back — that’s the point to call. Persistent alarms after a reset usually mean a real component fault, and pushing through them risks turning a simple repair into a bigger one. Keith covers HAAS® breakdowns across the UK with same-day phone diagnosis.
A note on this guide. Alarm wording and numbering can vary by HAAS® machine model and software revision. The descriptions here are written in plain English to help you understand what the machine is reporting and what to check first — they’re not a substitute for the official HAAS® operator manual or for a qualified service engineer’s diagnosis. Always confirm the exact alarm message on your screen and consult your machine’s documentation before attempting any repair.