Set XY plane. Planes are used with arcs, circles and cycles.
G17 is a G-code used to select the XY plane for the G02 and G03 commands. It is used to specify that the circular interpolation is to be performed in the XY plane. This is the default plane for circular interpolation and is usually used for operations such as drilling or boring.
G18, G19 are other codes used to select different planes for circular interpolation. G18 selects the XZ plane and G19 selects the YZ plane.
For example, G17 G03 X10 Y5 Z0 I0 J0 K1 F100 would move the tool in a counter-clockwise arc in the XY plane, with the center of the arc at coordinates (0,0), ending at coordinates (10,5), at a feed rate of 100 units per minute.
G17
G17