A G-code word always consists of a letter and a number, for example X12.5 or F800. Besides G and M there are these words. Upper and lower case and spaces do not matter, g1x10 is the same as G1 X10.
X Y Z · Axes
Axis targets in mm. X is left/right, Y front/back, Z up/down. In the app Z = 0 is on the material surface; negative Z values go into the material.
F · Feed rate
Cutting speed in mm/min. Applies to G1, G2, G3 and probing until a new value arrives. Too high breaks bits, too low burns wood. Values are in the cutting data.
Example:
G1 X100 F1200S · Spindle speed
Spindle speed in rpm (or laser power). For the value to be right, $30 must match the spindle. With spindles without speed control you set the speed on the dial.
Example:
M3 S12000I J K · Arc centre
Distance of the arc centre from the arc start in X (I), Y (J) and Z (K). Belongs to G2 and G3.
R · Arc radius
Radius of an arc instead of I/J. Negative means the larger of the two possible arcs. Not suitable for full circles.
P · Parameter
Number for a command: dwell time for G4 (seconds), coordinate system for G10 (1 = G54).
L · Type for G10
For G10 selects how the value is meant: L2 offset directly, L20 current position becomes the value.
N · Line number
Number at the start of a line, for orientation only. Grbl ignores it.
T · Tool number
Selects a tool. Grbl 1.1 only remembers the number; you have to change by hand.
( ) ; · Comments
Text in round brackets or after a semicolon is a comment and is not executed. The app writes bit name and part into its programs this way.
Example:
(3 mm bit, profile)
G0 Z5 ; safe height