What is the function of the G28 code in CNC programming?

The G28 code in CNC programming is specifically designed for zero return, also known as a return to home position. When this code is executed, it instructs the machine to move to a predefined reference point, which is typically set at the home or zero position of each axis. This is a crucial function in machining because it allows the operator to ensure that the machine is calibrated correctly and that tools are positioned accurately before embarking on a new machining operation.

Returning to the home position is often conducted after a tool change or whenever the machine needs to reset its position. It also assists in maintaining the integrity of the machining process by ensuring that the machine starts from a known point, safeguarding against potential errors that could arise from misalignment or incorrect positioning.

In contrast, the functions associated with the other options are distinct from the G28 command. Tool changes, program stops, and spindle speed control each involve separate codes and command structures that serve specific operational needs within CNC programming.