Which G-code command would you use to change the units from inches to millimeters?

The command used to change the units from inches to millimeters is G21. This G-code is specifically designated for setting the machine to use metric units, which include millimeters for distance measurements.

When working with CNC machines, understanding units of measurement is crucial as it directly impacts the precision and accuracy of the machining process. By using G21, the programmer defines the coordinate values in millimeters, ensuring that the tool movements and programming tasks are appropriately scaled for the metric system.

In contrast, other commands serve different purposes. For example, G20 is used to switch from metric to imperial units (inches), while G28 pertains to machine home positioning. Furthermore, G90 is related to setting absolute positioning mode, not specifically about unit conversion. Understanding these distinctions is key for effective CNC programming and operation.