Tool length offset (G43) in CNC Programming

Introduction

Tool length offset (G43) helps the CNC machine know the exact length of the tool. This makes sure the cutting starts at the right height.

When changing tools with different lengths during a CNC program.

To avoid crashing the tool into the workpiece by adjusting the Z-axis.

When precise depth control is needed for drilling or milling.

To save time by using preset tool length values instead of measuring each time.

Syntax

CNC Programming

G43 H<tool_length_offset_number> Z<position>

G43 activates the tool length offset.

H specifies which tool length offset number to use from the tool offset table.

Examples

Use tool length offset number 1 and move the tool to Z=5.0 considering the offset.

CNC Programming

G43 H01 Z5.0

Apply tool length offset number 2 and position the tool at Z=0.0 after offset.

CNC Programming

G43 H2 Z0.0

Sample Program

This program changes to tool 1, applies its length offset (H1), moves the tool to Z=50.0 above the workpiece, then cuts down to Z=-5.0 at feed rate 100, and finally retracts to Z=50.0 before ending.

CNC Programming

N10 T1 M06
N20 G90 G54
N30 G43 H1 Z50.0
N40 G01 Z-5.0 F100
N50 G00 Z50.0
N60 M30

Important Notes

Always set the correct tool length offset number (H) matching the tool in use.

G43 works only in absolute positioning mode (G90).

Tool length offsets are stored in the machine's tool offset table and must be measured beforehand.

Summary

G43 tells the machine to use a tool length offset for accurate Z positioning.

Use H number to select the correct offset for the current tool.

This prevents tool crashes and ensures precise cutting depths.