Tool numbering and selection (T word) in CNC Programming - Step-by-Step Execution

Concept Flow - Tool numbering and selection (T word)

Start Program

↓

Select Tool Number (T#)

↓

Call Tool Change Command (M6)

↓

Wait for Tool Change Completion

↓

Execute Machining with Selected Tool

↓

End Program

The CNC program starts by selecting a tool number using the T word, then calls the tool change command M6, waits for the tool to change, and proceeds with machining using the selected tool.

Execution Sample

CNC Programming

N10 T02 M06
N20 G00 X0 Y0
N30 M03 S1500
N40 G01 X50 Y50 F100
N50 M05
N60 M30

This CNC code selects tool 2, changes to it, moves to start position, starts spindle, cuts a line, stops spindle, and ends the program.

Execution Table

Step	Code Line	Action	Tool Selected	Spindle Status	Position	Output
1	N10 T02 M06	Select tool 2 and execute tool change	2	Off	(0,0)	Tool 2 loaded
2	N20 G00 X0 Y0	Rapid move to X0 Y0	2	Off	(0,0)	Position set
3	N30 M03 S1500	Start spindle at 1500 RPM	2	On	(0,0)	Spindle running
4	N40 G01 X50 Y50 F100	Linear cut to X50 Y50 at feed 100	2	On	(50,50)	Cutting path
5	N50 M05	Stop spindle	2	Off	(50,50)	Spindle stopped
6	N60 M30	End program	2	Off	(50,50)	Program ended

💡 Program ends after line N60 with M30 command

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	Final
Tool Number	None	2	2	2	2	2	2
Spindle Status	Off	Off	Off	On	On	Off	Off
Position	(0,0)	(0,0)	(0,0)	(0,0)	(50,50)	(50,50)	(50,50)

Key Moments - 3 Insights

Why do we need to use the T word before M06?

The T word tells the machine which tool number to select. M06 then triggers the tool change to that selected tool. Without T, the machine won't know which tool to load (see execution_table step 1).

What happens if we try to move before the tool change completes?

The machine waits for the tool change to finish before moving. This ensures the correct tool is in place for machining (see execution_table step 2 after tool change).

Does the spindle start automatically after tool change?

No, spindle start is a separate command (M03). Tool change only loads the tool; spindle must be started explicitly (see execution_table step 3).

Visual Quiz - 3 Questions

Look at the execution table, what tool is selected after step 1?

A Tool 1

B Tool 2

C No tool selected

D Tool 3

💡 Hint

Check the 'Tool Selected' column in execution_table row for step 1

At which step does the spindle start running?

A Step 3

B Step 2

C Step 4

D Step 5

💡 Hint

Look at the 'Spindle Status' column in execution_table to find when it changes to 'On'

If we change T02 to T03 in line N10, what changes in the execution table?

A Position changes at step 2

B Spindle starts earlier

C Tool Selected changes to 3 at step 1

D Program ends earlier

💡 Hint

Focus on the 'Tool Selected' column in execution_table step 1

Concept Snapshot

Tool numbering uses T followed by a number (e.g., T02) to select a tool.
M06 command triggers the tool change to the selected tool.
Tool change must complete before machining moves start.
Spindle start (M03) is separate from tool change.
Program ends with M30.
Always select tool before machining commands.

Full Transcript

In CNC programming, the T word followed by a number selects the tool to use. The M06 command tells the machine to change to that tool. The program waits for the tool change to finish before moving or starting the spindle. Spindle start is done with M03 and speed set by S command. The example program selects tool 2 with T02, changes tool with M06, moves to start position, starts spindle, cuts a line, stops spindle, and ends the program with M30. Variables like tool number, spindle status, and position change step by step as shown in the execution table. Key points are to always select the tool before M06, wait for tool change completion, and start spindle separately. The visual quiz tests understanding of tool selection, spindle start timing, and effects of changing tool number.

Practice

1. What does the T[number] command do in a CNC program?

easy

A. It starts the spindle rotation.

B. It moves the machine to a coordinate.

C. It stops the machine.

D. It selects the tool number to be used.

Solution

1. Step 1: Understand the role of T[number]

   The T[number] command tells the CNC machine which tool number to select.

2. Step 2: Differentiate from other commands

   Other commands like spindle start or movement do not use T[number].

3. Final Answer:

   It selects the tool number to be used. -> Option D

4. Quick Check:

   Tool selection = T[number] command [OK]

Hint: T[number] always means tool selection in CNC [OK]

Common Mistakes:

• Confusing T command with spindle or movement commands
• Thinking T[number] moves the machine
• Assuming T[number] starts or stops the spindle

2. Which of the following is the correct syntax to change to tool number 5 in a CNC program?

easy

A. T5 M6

B. M6 T5

C. T M6 5

D. M5 T6

Solution

1. Step 1: Recall correct command order

   The correct syntax is T[number] M6 to select and change the tool.

2. Step 2: Match syntax to tool 5

   For tool 5, it becomes T5 M6.

3. Final Answer:

   T5 M6 -> Option A

4. Quick Check:

   Tool change syntax = T[number] M6 [OK]

Hint: Tool number first (T5), then M6 to change tool [OK]

Common Mistakes:

• Swapping order of T and M6 commands
• Using M6 before T[number]
• Mixing tool number and command letters

3. What will be the effect of the following CNC code snippet?

T3 M6
G00 X10 Y10

medium

A. The machine moves to X10 Y10 without changing the tool.

B. The machine moves to X10 Y10 using tool 3 after changing to it.

C. The tool change command is ignored and only movement happens.

D. The machine stops due to syntax error.

Solution

1. Step 1: Analyze tool change command

   T3 M6 selects and changes to tool number 3.

2. Step 2: Analyze movement command

   G00 X10 Y10 moves the machine quickly to coordinates X10 Y10.

3. Final Answer:

   The machine moves to X10 Y10 using tool 3 after changing to it. -> Option B

4. Quick Check:

   Tool 3 selected then move = The machine moves to X10 Y10 using tool 3 after changing to it. [OK]

Hint: T3 M6 changes tool, next line moves machine [OK]

Common Mistakes:

• Ignoring the tool change command
• Assuming tool change happens after movement
• Thinking syntax error occurs

4. Identify the error in this CNC tool change command:

T7 M06

medium

A. M06 should be lowercase m6.

B. There should be a space between T7 and M06.

C. The command is correct and will work as expected.

D. The tool number 7 is invalid.

Solution

1. Step 1: Check command syntax

   T7 M06 is a valid tool change command; uppercase or lowercase M6 is accepted in most CNC controls.

2. Step 2: Validate spacing and tool number

   Space between commands is optional; tool number 7 is valid if defined in tool library.

3. Final Answer:

   The command is correct and will work as expected. -> Option C

4. Quick Check:

   Valid tool change syntax = The command is correct and will work as expected. [OK]

Hint: M6 can be uppercase or lowercase; spacing is flexible [OK]

Common Mistakes:

• Thinking uppercase M06 is invalid
• Expecting mandatory space between commands
• Assuming tool number 7 is always invalid

5. You want to write a CNC program that changes tools in this order: tool 2, then tool 10, then tool 5. Which sequence correctly uses tool numbering and selection commands?

hard

A. T2 M6
T10 M6
T5 M6

B. M6 T2
M6 T10
M6 T5

C. T2 M6
M6 T10
T5 M6

D. T2
M6 T10
M6 T5

Solution

1. Step 1: Recall correct tool change syntax

   Each tool change must use T[number] M6 to select and change the tool.

2. Step 2: Check each line for correct order

   T2 M6 T10 M6 T5 M6 correctly uses T2 M6, T10 M6, and T5 M6 in sequence.

3. Final Answer:

   T2 M6 T10 M6 T5 M6 -> Option A

4. Quick Check:

   Tool change sequence = T[number] M6 each time [OK]

Hint: Always use T[number] M6 for each tool change line [OK]

Common Mistakes:

• Putting M6 before T[number]
• Missing M6 on some tool changes
• Splitting commands incorrectly across lines