How to Use If Then in CNC Macro Programming

In CNC macro programming, use the IF statement followed by a condition and THEN to execute commands when the condition is true. The syntax is IF [condition] THEN [commands], allowing decision-making in your CNC programs.

Syntax

The IF THEN statement in CNC macro lets you run commands only if a condition is true. It checks a condition and executes the following commands if the condition holds.

• IF: starts the condition check
• condition: a logical test (e.g., #100 EQ 1 means variable 100 equals 1)
• THEN: separates the condition from the commands to run
• commands: CNC instructions or macro variables to execute if true

cnc_macro

IF [condition] THEN [commands]

Example

This example checks if variable #100 equals 1, then moves the tool to position X100 Y100. If the condition is false, it skips the move.

cnc_macro

O1000;
#100=1;
IF [#100 EQ 1] THEN GOTO 10;
GOTO 20;
N10 G01 X100 Y100 F100;
N20 M30;

Output

The program moves the tool to X100 Y100 only if #100 equals 1; otherwise, it skips that move.

Common Pitfalls

Common mistakes include:

• Forgetting to enclose the condition in square brackets [].
• Using incorrect comparison operators (use EQ, NE, GT, LT, etc., not symbols like == or !=).
• Not following THEN with valid commands or labels.
• Missing line numbers or labels when using GOTO inside IF THEN.

Correct usage example:

cnc_macro

IF [#100 EQ 1] THEN GOTO 10;
! Wrong: IF #100 == 1 THEN GOTO 10;
! Wrong: IF [#100 EQ 1] GOTO 10;

Quick Reference

Element	Description	Example
IF	Starts the condition check	IF [#100 EQ 1] THEN ...
Condition	Logical test inside brackets	[#100 GT 0]
THEN	Separates condition from commands	THEN GOTO 10
Commands	Actions if condition is true	GOTO 10, M98, variable assignments
Comparison Operators	Used in conditions	EQ (equal), NE (not equal), GT (greater), LT (less)

Key Takeaways

Use IF [condition] THEN [commands] to run commands only when the condition is true.

Always enclose conditions in square brackets and use CNC macro comparison operators like EQ, NE, GT, LT.

Follow THEN with valid CNC commands or labels to avoid errors.

Use line numbers or labels with GOTO inside IF THEN for clear program flow.

Test your macro logic carefully to prevent unexpected machine moves.