This guide is a practical, real-world CNC alarm encyclopedia focused on the exact error messages operators and programmers search for every single day. It combines Fanuc, Haas, and Siemens alarm logic with real G-code mistakes, hidden root causes, and professional prevention patterns used in high-end production shops. This is not a generic alarm list — it is a crash-prevention and profit-protection reference designed to stay relevant for years.
1. The Most Googled CNC Alarm of All Time: Overtravel / Soft Limit Exceeded
Common Alarm Messages
- FANUC: 500 / 501 / 502 Overtravel
- HAAS: Axis Over Travel
- SIEMENS: Travel Range Exceeded
The Real Cause (Not What Manuals Say)
The most common cause is absolute rapid moves without machine-awareness, especially:
G00 Z100
G00 X0 Y0
On many machines, Z+100 is ABOVE machine limits, not “safe”.
Why G00 Z100 Is Dangerous
- Z100 is interpreted in work coordinates, not machine coordinates
- On tall fixtures or rotated setups, this causes instant overtravel
- Operators assume “positive Z is always safe” — this is false
Professional Safe Pattern (Used in Aerospace Shops)
G91 G28 Z0
G90
or
G53 Z0
Never use G00 Z100 unless you fully understand the machine envelope.
2. Servo Alarm / Excess Error (Silent Crash Warning)
Common Alarms
- FANUC: 414 / 424 / 434
- HAAS: Servo Error Too Large
- SIEMENS: Axis Following Error
Hidden Causes
- Acceleration too aggressive after CAM
- Heavy tool + high feed + small radius
- Tool hits material harder than servo can react
Typical G-code Trigger
G01 X120. F4000
on a heavy spindle or large face mill.
Pro Fix
- Reduce feed on entry moves
- Add lead-ins
- Use G187 (Haas) or smoothing parameters
- Avoid sharp direction changes at high feed
3. Alarm Caused by G02 / G03 Arcs (Top Programming Error)
Common Alarms
- FANUC: 33 / 34 Illegal Circular Interpolation
- HAAS: Invalid Arc
- SIEMENS: Circle Geometry Error
Real Cause
- I J values don’t match start/end points
- CAM rounding error
- Switching planes (G17/G18/G19) incorrectly
Crash-Prone Example
G17
G02 X50 Y20 I10 J0
If start point is wrong by 0.01 mm → alarm.
Professional Rule
- Never hand-edit arcs unless necessary
- If unsure, replace arc with linear moves
- Always verify plane before arc commands
4. Tool Length Compensation Alarm (One of the Most Expensive Errors)
Common Alarms
- FANUC: Tool Length Offset Error
- HAAS: No Tool Length Offset
- SIEMENS: Tool Compensation Not Active
Real Cause
- G43 missing
- Wrong H number
- Tool change without offset reset
Real Crash Scenario
T12 M06
G00 Z5
Tool crashes because no length compensation active.
Mandatory Safe Pattern
T12 M06
G43 H12 Z100
Never move Z toward the part before G43.
5. Alarm Triggered by Wrong Coordinate System (G54–G59)
Common Alarms
- Unexpected overtravel
- Tool cutting air
- Tool plunges into fixture
Real Cause
- Wrong work offset selected
- Offset overwritten by G10
- Operator forgets G54 change
Professional Prevention
- Always display active work offset
- Lock offsets in production
- Use probing to auto-verify offsets
6. Feedrate & RPM Mismatch Alarms
Common Issues
- F value too high for tapping
- RPM not synchronized
- Wrong G98 / G99 usage
Classic Example
G84 Z-15 F1.25
But spindle speed too high → broken tap.
Pro Tip
For rigid tapping:
Feed = Pitch × RPM
Always calculate — never guess.
7. Hidden Alarm Source: Incremental Mode (G91 Left Active)
Real Scenario
G91
G00 Z10
Next block:
G00 Z10
Tool keeps moving up until alarm or crash.
Professional Rule
Always return to absolute mode:
G90
Especially after homing or probing macros.
8. Alarm Caused by CAM Postprocessor Errors
Common Signs
- Random overtravels
- Impossible arcs
- Sudden feed spikes
Root Cause
- Postprocessor not matched to control
- Metric/inch mismatch
- Rotary axis limits ignored
Pro Fix
- Verify post for exact machine model
- Simulate with machine limits ON
- Never trust CAM blindly
9. Operator Mistakes That Create 80% of Alarms
- Using G00 instead of G01 near the part
- Assuming Z+ is always safe
- Ignoring active plane (G17/G18/G19)
- Forgetting G43
- Forgetting G90
- Copy-paste from old programs
10. Crash-Proof Programming Checklist (Professional Standard)
Before cycle start:
- Active work offset verified
- G90 confirmed
- G43 active
- Safe Z move using G53 or G28
- Correct plane selected
- Feed and RPM reviewed
If you follow this checklist, most CNC alarms disappear permanently.
Final Summary
The CNC alarms operators search for every day are rarely “machine problems” — they are almost always logic problems in G-code. Understanding how commands like G00, G43, G90, G53, and work offsets truly behave separates amateur programming from professional, crash-proof machining. This guide is designed to be a long-term reference that operators, programmers, and shop owners return to again and again — because alarms cost money, and knowledge prevents them.
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