Spindle speed (S word) and direction (M03, M04) in CNC Programming - Step-by-Step Execution

Concept Flow - Spindle speed (S word) and direction (M03, M04)

Start Program

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Set Spindle Speed with S word

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Set Spindle Direction

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Spindle Spins

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Continue Machining

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End Program

The program sets spindle speed using the S word, then chooses direction with M03 (clockwise) or M04 (counterclockwise), then the spindle spins accordingly before machining continues.

Execution Sample

CNC Programming

N10 S1200 M03
N20 G01 X50 Y50 F100
N30 M05
N40 M30

Sets spindle speed to 1200 RPM clockwise, moves tool, stops spindle, ends program.

Execution Table

Step	Code Line	Action	Spindle Speed (RPM)	Spindle Direction	Output/Effect
1	N10 S1200 M03	Set spindle speed and direction	1200	Clockwise (M03)	Spindle starts spinning clockwise at 1200 RPM
2	N20 G01 X50 Y50 F100	Linear move with feedrate	1200	Clockwise (M03)	Tool moves to X50 Y50 while spindle spins
3	N30 M05	Stop spindle	0	Stopped	Spindle stops spinning
4	N40 M30	End program	0	Stopped	Program ends
5					Execution stops: Program end reached

💡 Program ends at N40 with M30 command

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
Spindle Speed (RPM)	0	1200	1200	0	0
Spindle Direction	Stopped	Clockwise (M03)	Clockwise (M03)	Stopped	Stopped

Key Moments - 3 Insights

Why does the spindle speed stay the same during the move command (N20)?

Because spindle speed is set once at N10 and remains until changed or stopped, as shown in execution_table rows 1 and 2.

What happens if M04 is used instead of M03 at N10?

The spindle direction changes to counterclockwise, but speed setting with S word remains the same. This would be reflected in the spindle direction column changing to 'Counterclockwise (M04)'.

Why is spindle speed zero after M05 command?

M05 stops the spindle, so speed drops to zero immediately, as shown in execution_table row 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the spindle direction after step 2?

A Stopped

B Counterclockwise

C Clockwise

D Not set

💡 Hint

Check the 'Spindle Direction' column at step 2 in the execution_table.

At which step does the spindle speed become zero?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the 'Spindle Speed (RPM)' column in execution_table rows.

If we change M03 to M04 in line N10, what changes in the execution table?

A Spindle speed changes to zero

B Spindle direction changes to Counterclockwise

C Program ends earlier

D No change

💡 Hint

Compare spindle direction in execution_table row 1 with M03 vs M04.

Concept Snapshot

Spindle speed is set with the S word (e.g., S1200 for 1200 RPM).
Spindle direction is set with M03 (clockwise) or M04 (counterclockwise).
Spindle spins at set speed and direction until stopped with M05.
Commands run in sequence: set speed/direction, move tool, stop spindle, end program.
Changing M03 to M04 reverses spindle rotation direction.

Full Transcript

This CNC program example shows how spindle speed and direction are controlled. First, the spindle speed is set using the S word with a number representing RPM, for example, S1200 means 1200 revolutions per minute. Then the spindle direction is set using M03 for clockwise rotation or M04 for counterclockwise. The spindle starts spinning at the set speed and direction. The tool then moves to a position while the spindle spins. The spindle is stopped with M05, and the program ends with M30. The execution table traces each step, showing spindle speed and direction changes. The variable tracker shows spindle speed and direction values after each step. Key moments clarify why spindle speed stays constant during moves, what happens if direction changes, and why spindle speed drops to zero after stopping. The visual quiz tests understanding of spindle direction and speed changes at different steps. The concept snapshot summarizes how to set spindle speed and direction in CNC programming.