G43 applies a tool length offset so Z moves reference the part surface instead of the spindle face. Each tool measures a different length, and its offset lives in a numbered register called with an H word.
Format
G43 H__ Z__ (H = offset register, usually the tool number)
How it works
- Store each tool length offset in the control, then call G43 with the matching H number.
- Activate it on the first Z move after a tool change.
- G49 cancels tool length compensation.
Example
T01 M06
G43 H01 Z1.0 (apply tool 1 length, rapid to Z1.0)
G43 H01 Z1.0 (apply tool 1 length, rapid to Z1.0)
FAQ
What happens if I forget to cancel G43 with G49? The tool length offset stays active, which can apply an unintended Z offset to the next tool or operation. Most programs cancel with G49 before a tool change or at the end of the program to avoid this.
What’s the difference between G43 and G44? G43 applies a positive tool length offset, the more common convention, while G44, rarely used on modern controls, applies it in the opposite direction. Nearly all current programming standardizes on G43.
Related: G28 and Setup & Workholding.