G90 and G91 - Absolute and Incremental Positioning Commands in CNC Milling
CNC (Computer Numerical Control) milling is a powerful machining method used to machine complex components in various shapes, sizes, and forms with precision accuracy. To ensure precise motion control, CNC machines are equipped with G90 and G91 commands. G90 and G91 refer to absolute and incremental positioning commands respectively, which help the machine accurately position its axis and position material to precise locations. With that said, let us understand what G90 and G91 commands are and how they work.
What is G90?
G90 is an absolute positioning command that instructs the CNC machine to move its axis of the control to its designated coordinate location. This command is usually used when the tool is to move from one precise location to another. The command is activated by G90 X# Y# Z# (or any variation thereof). Here, # refers to the precise location on each of the three axis at which the tool must move. For example, if the CNC controller is given the command G90 X5 Y5 Z5, it will move the tool to coordinates 5, 5 and 5 units respectively on the three axes.
What is G91?
G91 is an incremental positioning command that instructs the CNC machine to move its axis a specified number of units from its current position. This command is usually used when the tool needs to make a small movement towards its next designed coordinate location. It is activated by G91 X# Y# Z# (or any variation thereof). Here, # refers to the number of units which the tool must move on each of the three axes. For example, if the CNC controller is given the command G91 X1 Y1 Z1, it will move the tool 1 unit in each of the three axes from its current position.
How do G90 and G91 Commands work?
The way G90 and G91 commands are executed is slightly different. G90 commands are executed as absolute positioning commands and therefore the machine will move directly to its designated location without any intermediate motion. On the other hand, G91 commands are executed as incremental positioning commands and therefore the machine will move relative to its current position. For example, if the machine is at coordinate location 10, 10 and 10 and receives a G91 command of X5 Y5 Z5, it will move to coordinate location 15, 15 and 15 accordingly.
Conclusion
G90 and G91 commands are important tools used for precise positioning during CNC machining. G90 commands are used for absolute positioning and G91 commands are used for incremental positioning. By understanding how to use these commands in CNC machines, engineers can ensure precise positioning of their tools and parts every time.
