If you want to control the CNC machine tool and let the machine tool work according to your intention, you must first understand the "machine tool language", that is, the CNC command. For example, G28 returns to the origin of the machine tool. You input G91G28X0Y0Z0 in the machine tool. After the program segment runs, the machine tool understands what you mean, and it will quickly return to the origin of the machine tool.
But some beginners don't understand why the master uses G91G28X0Y0Z0 instead of G90 G28X0Y0Z0 when writing programs?
In fact, both methods can be used, let me tell you why?
The meaning of the G28 command is to return to the origin of the machine tool, and the X, Y, and Z coordinate values behind this command are the middle points that the tool must pass before returning to the origin of the machine tool.
Say important things three times:
The X, Y, and Z coordinate values behind G28 are the intermediate points that the tool must pass before returning to the machine origin.
The X, Y, and Z coordinate values behind G28 are the intermediate points that the tool must pass before returning to the machine origin.
The X, Y, and Z coordinate values behind G28 are the intermediate points that the tool must pass before returning to the machine origin.
Why does it need to go through the middle point before returning to the machine origin?
The purpose of setting the middle point is to prevent the tool from interfering with the workpiece or fixture when returning to the origin.
Then return to the middle point, you can choose G90 mode or G91 mode.
Such as G91G28Z0
After G28 passes Z=0 point, return to the origin
Because Z=0 is commanded by G91, the tool has no movement amount, that is, the current position of the tool directly returns to the machine origin. As shown below:
For example, the following program segment
...
G0Z50
G90G28Z0
M30
After we finish cutting the part, for example, lift the tool at Z=50, then the machine tool runs the G90G28Z0 program segment, the machine tool understands that you are in the G90 mode, then return to Z=0 first, and then return to the machine origin, as shown in the figure below:
This is why when G90G28Z0 is used, the tool may return to Z=0 first, and then return to the machine origin. So it is recommended to use incremental mode G91G28Z0.
