This guide is a long-term reference resource designed to answer the most searched CNC questions on the internet: why machines alarm, why programs crash, and how common G-code mistakes silently destroy tools, parts, and machines. It is written to remain relevant for years, covering Fanuc, Haas, and Siemens controls with real-world causes, examples, and prevention patterns used by professional CNC programmers.

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SECTION 1: MOST COMMON CNC ALARM TYPES (REAL SHOP DATA)

— FANUC ALARMS —

• Alarm 100 / 101 – Overtravel (X/Y/Z)
  Cause: Toolpath exceeds soft or hard limits
  Hidden reason: G28/G30 misuse, wrong work offset, missing G53 safety move
• Alarm 300 – Illegal G-code
  Cause: Unsupported G-code or wrong modal group
  Example: Using G68 on machines without rotation option
• Alarm 401 / 402 – Servo overload
  Cause: Excessive acceleration or feedrate
  Hidden reason: CAM output too dense, missing smoothing (G05.1 / G131)
• Alarm 510 – Spindle overload
  Cause: Feed too high or wrong tool engagement
  Hidden reason: G00 Z-100 crash due to missing clearance logic

— HAAS ALARMS —

• Alarm 144 – Feedrate too high
  Cause: Incorrect inverse time feed (G93)
  Example: Forgetting to cancel G93 before G01 Z moves
• Alarm 160 – Tool too long
  Cause: Tool length exceeds machine limit
  Hidden reason: Wrong H offset or probe failure
• Alarm 362 – Tool change interference
  Cause: Tool not at safe Z
  Hidden reason: Missing G28 G91 Z0 before M06

— SIEMENS ALARMS —

• 14010 – Axis limit violation
  Cause: Wrong coordinate system or transformation active
  Example: G68 active during machine move
• 20001 – Channel synchronization error
  Cause: Feed/spindle mismatch
  Hidden reason: Manual threading with wrong feed logic

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SECTION 2: MOST SEARCHED G-CODE MISTAKES (CRASH CLASSICS)

— G00 Z-100 (THE MOST DANGEROUS LINE EVER WRITTEN) —
Why it crashes:

• Absolute mode active (G90)
• Wrong work offset
• Z zero set on table instead of part
• Tool length offset missing

Safe pattern:
G91
G00 Z50.
G90

Never use blind absolute Z rapids.

— FORGOTTEN MODALS —

• G93 not cancelled → inverse feed disaster
• G68 not cancelled → rotated machine home crash
• G91 left active → runaway axis moves
• G54 not restored → cutting in wrong fixture

Mandatory safety reset block:
G90 G94 G17 G40 G49 G80 G69

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SECTION 3: TOP PROGRAMMING ERRORS THAT CAUSE CRASHES

1) Tool length offset called AFTER Z move
Wrong:
G00 Z5.
G43 H12

Correct:
G43 H12 Z5.

2) Tool change without retract
Wrong:
M06

Correct:
G91 G28 Z0.
G90
M06

3) Using G28 incorrectly
Wrong:
G28 X0 Y0 Z0

Correct:
G91 G28 Z0.
G91 G28 X0 Y0
G90

4) Mixing G53 and work coordinates
Wrong:
G68 active
G53 Z0

Always cancel transformations before G53.

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SECTION 4: MOST FREQUENTLY ASKED CNC QUESTIONS (FAQ)

Q: Why does my program run fine in air but crash on material?
A: Tool length offset error, missing G43 on first Z move

Q: Why does the machine suddenly move extremely slow?
A: G93 inverse time feed still active

Q: Why does tool plunge at rapid speed?
A: Missing G01 before Z move or modal feed cancelled

Q: Why does finishing look faceted?
A: Missing smoothing (G05.1 / G187 / G131)

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SECTION 5: CRASH-PROOF PROGRAMMING PATTERNS (PRO LEVEL)

Always start with:

• Modal reset line
• Safe Z retract
• Work offset verification
• Tool length activation before motion

Professional safety header:
%
G90 G17 G40 G49 G80 G94 G69
G91 G28 Z0.
G90

Professional end-of-program:
G91 G28 Z0.
G91 G28 X0 Y0
G90
M30

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SECTION 6: WHY THIS CONTENT STAYS VIRAL

• CNC alarms never change fundamentally
• New machinists search the same errors every year
• Shops lose money daily from these mistakes
• This page answers “why did my CNC crash?” better than manuals
• Perfect for bookmarks, forums, Reddit, Facebook groups, and training links

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FINAL SUMMARY

This CNC Error Encyclopedia is designed as a permanent reference that CNC users return to repeatedly. By combining real alarm codes, real crash causes, and proven safety patterns, it delivers immediate value to beginners and professionals alike. This type of content consistently ranks, attracts backlinks, and generates long-term organic traffic because CNC errors are universal, costly, and always searched.