CNC Safety Lines Explained

January 13, 2021 3:25 pm


Why do we need safety lines within our CNC program? Here’s a simple explanation from @G-Code Tutor​.

Safety lines are typically added at the beginning of a G-code program to put the CNC machine into a default state. This means that if we stop the program and re-run it using a different tool, we know for sure that the machine is in a safe state to run. Safety lines don’t always look the same. They vary depending on the needs of the CNC programmer, the type of machine tool, and the program running.

A typical safety line is composed of various G-codes, written in no-specific order. Some of the most common ones are:

G90/G91 – Absolute/Incremental positioning
G54 – Workshift datum
G90.1/G91.1 – Absolute/incremental distance mode for I, J, and K offsets G40 – Cancel cutter compensation
G17 – XY plane selection
G18 – ZX plane selection
G19 – YZ plane selection
G20/G21 – Imperial/metric units
G80 – Cancel any active cycle

To learn more about safety lines within G-code programming, visit

Stay tuned for more machining videos!

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