M00 vs M01 vs M02 vs M30: CNC Program Stops and End Commands Explained

M00 vs M01 vs M02 vs M30: CNC Program Stops and End Commands Explained

Every CNC program needs to pause, stop, or reset at the right time — and that’s where M00, M01, M02, and M30 come into play.

While they seem similar, each serves a specific purpose in controlling program flow, especially during tool changes, inspections, or job transitions.

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🧠 Quick Definitions

M-Code	Description	Requires Operator Action?	Resumes From?
M00	Unconditional stop	Yes	Same line
M01	Optional stop (only if enabled)	Yes (if Optional Stop ON)	Same line
M02	End of program	No	Start of program
M30	End and rewind (Reset & Start)	No	Beginning again

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🟨 M00 – Unconditional Program Stop

M00

• Pauses execution immediately
• Machine stops: spindle, feed, coolant
• Operator must press Cycle Start to continue
• Use for mandatory inspections, manual tool changes, or part clearance

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🟩 M01 – Optional Stop (With Toggle)

M01

• Acts only if Optional Stop switch is ON on the control panel
• Skipped entirely if switch is OFF
• Great for semi-automated inspection points or conditional stops

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🔧 Example:

...
G01 Z-15 F150
M01         ; Stop only if toggle ON
G00 Z100
...

Ideal during prototype runs, can be skipped in production.

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🟥 M02 – End of Program

M02

• Tells the control that the program has ended
• Most machines stop completely
• Does not rewind the program
• Use for one-time jobs or subprograms

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🟦 M30 – End of Program + Reset + Rewind

M30

• Ends the program and resets the program counter
• Rewinds to the start (line 0 or O-code)
• Most commonly used at the end of main programs
• Used for repeatable cycles, automated loops, or part counters

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🔁 Typical Usage Flow

%
O1000
(Tool 1 Roughing)
...
M00    ; Manual inspection
...

(Tool 2 Finishing)
...
M01    ; Optional check
...

M30    ; End, reset and ready for next part
%

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✅ Best Practices

• Use M00 only for critical manual interventions
• Use M01 for optional quality checks
• Use M30 at the end of main programs
• Use M02 in subprograms or when no rewind is desired
• Always comment the reason for stops (; Check bore size, etc.)

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🧠 Summary Table

M-Code	Function	Used In	Operator Required?	Rewinds?
M00	Unconditional stop	Setup/manual check	✅ Yes	❌ No
M01	Optional stop (toggle)	Optional inspections	✅ (if ON)	❌ No
M02	End of program	Subprograms/one-offs	❌ No	❌ No
M30	End + rewind	Main program ends	❌ No	✅ Yes

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▶️ Coming Up: G17, G18, G19 – Plane Selection for Circular Interpolation Explained