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Tool numbering and selection (T word) in CNC Programming

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Introduction

Tool numbering and selection lets the CNC machine know which tool to use for cutting. It tells the machine to pick the right tool from the tool holder.

When starting a CNC program to choose the first tool.
When changing tools during a machining process.
When setting up the machine to use a specific tool for a job.
When programming multiple operations that need different tools.
Syntax
CNC Programming
T[number] M6

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

M6 is the command to change the tool.

Examples
Selects tool number 1 and changes to it.
CNC Programming
T1 M6
Selects tool number 5 and changes to it.
CNC Programming
T5 M6
Selects tool number 12 and changes to it.
CNC Programming
T12 M6
Sample Program

This simple CNC program selects tool number 3 using T3 M6. Then it sets positioning and moves to the start point.

CNC Programming
O1000 (Sample program)
T3 M6 (Select tool 3 and change)
G90 G54 (Absolute positioning, work offset)
G0 X0 Y0 (Move to start position)
M30 (End program)
OutputSuccess
Important Notes

Always use M6 after T[number] to tell the machine to change tools.

Tool numbers must match the tools loaded in the machine's tool holder.

Some machines may require a pause or confirmation after tool change.

Summary

Tool numbering tells the machine which tool to use.

M6 command changes the tool to the selected number.

Use T[number] M6 to select and change tools in CNC programs.

Practice

(1/5)
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
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