G90 Absolute Programming and G91 Incremental Programming

Format

G90: absolute Programming
G91: incremental Programming

Description

G90: it denotes absolute programming; the programming value on each programming coordinate axis is with respect to the origin of current WCS.
G91: it denotes incremental programming; the programming value on each programming coordinate axis is with respect to the previous position, and the value equals the distance that the tool moves in each axis.

G90, as the default, and G91 are modal.

Selecting the right programming mode can simplify the programming. If the drawing dimension is given based on a fixed datum, it is better to adopt absolute programming mode; if the drawing dimension is given on the basis of space distance between contour apexes, it is better to adopt incremental programming mode.

CAUTION:

G90 and G91 cannot be used in the same program block. For example, G90 G91 G0 X10 is not allowed.

Programming Example

Sketch of programming with G90, G91 to make the tool move in sequence from origin to point 1, 2, and 3 is as follows:

Programming with G90
```
N01 X20 Y15
```
```
N02 X40 Y45
```
```
N03 X60 Y25
```
Programming with G91
```
N01 X20 Y15
```
```
N02 X20 Y30
```
```
N03 X20 Y-20
```