M01 Optional Stop in CNC Programming: What It Is and How It Works

In CNC programming, M01 is an optional stop command that pauses the machine only if the optional stop function is enabled on the CNC control panel. It allows operators to decide whether to stop the machine at specific points without forcing a stop every time the program runs.

How It Works

The M01 command acts like a checkpoint in a CNC program. When the machine reaches this command, it will pause only if the operator has turned on the optional stop feature on the control panel. If the optional stop is off, the machine ignores M01 and continues running without interruption.

Think of it like a traffic light that only turns red if a sensor detects a car. If the sensor is off, the light stays green and cars keep moving. This gives the operator control to pause the machine at certain points for checks or tool changes without stopping every time the program runs.

Example

This example shows a simple CNC program snippet using M01 to optionally pause after a drilling operation.

gcode

N10 G00 X10 Y10 Z5
N20 G81 R2 Z-10 F100
N30 M01
N40 G80
N50 M30

Output

The machine drills at X10 Y10, then pauses at line N30 only if optional stop is enabled; otherwise, it continues to line N40 and ends the program.

When to Use

Use M01 when you want to give the operator the choice to pause the machine at certain points without forcing a stop every time. This is useful for:

• Checking part quality during long runs
• Changing tools or fixtures without stopping the entire program
• Performing manual measurements or adjustments

It helps improve efficiency by avoiding unnecessary stops while still allowing control when needed.

Key Points

• M01 pauses only if optional stop is enabled on the CNC control panel.
• It differs from M00, which always stops the machine.
• Operators can enable or disable optional stops without changing the program.
• Useful for flexible control during automated machining.

Key Takeaways

M01 is an optional stop that pauses the CNC machine only if enabled by the operator.

It allows flexible pauses for checks or tool changes without forcing stops every run.

Operators control optional stops via the CNC control panel, not by changing the program.

M01 differs from M00, which always stops the machine.

Use M01 to improve machining efficiency and operator control.