P a g e | 11
G & M Code
G02/G03 – Arc Feed Move: Used to cut an arc at a federate specified by F. An arc is defined by its
start and end points, its radius or center point, a direction, and a plane. Direction is determined by
G02, clockwise, and G03, counterclockwise, when viewed from the plane’s positive direction (If XY
plane is selected look down so that the X axis positive direction is pointing to the right, and the Y axis
positive direction is pointing forward).See figure 2 for a graphic representation of the motion of a
G02. The start point is the current position of the machine. Specify the end point with X, Y, and Z. The
values input for the end point will depend on the current G90/G91 (abs/inc) setting of the machine.
Only the two points in the current plane are required for an arc. Adding in the third point will create a
helical interpolation.
Next is to specify the radius or the center point of the arc, only one or the other, not both.
To specify the radius, use R and input the actual radius of the desired arc, see Format 2.
When an arc is created knowing only start and end points and a radius there are two
possible solutions, an arc with a sweep less than 180° and one with sweep greater than 180°.
The sign of the radius value, positive or negative, determines which arc will be cut, see figure
3. A positive value for R cuts an arc with sweep less than 180°. A negative value for R cuts an
arc with sweep greater than 180°.
A more accurate and reliable way to define an arc is by specifying the center point, this is
done with arguments I, J, and K (See Format 1). The center point must be defined in the current
plane. I, J, and K correspond to X, Y, Z respectively; the current plane selection will determine
which two are used. XY plane (G17) would use I and J for example. Mach has two settings for
how I, J, and K should be specified, absolute and incremental. This setting can be changed by
G code, G90.1 and G91.1, or in the general tab in the Mach configuration. This setting is
independent of the G90/G91 setting. If arc center mode is set to incremental then I, J, K are
the distance and direction from the start point to the center point of the arc. If arc center mode
is set to absolute then I, J, K are the absolute position of the arc center point in the current user
coordinate system.
Format 1: (G17) G02/03 X__ Y__ I__ J__ F__
(G18) G02/03 X__ Z__ I__ K__ F__
(G19) G02/03 Y__ Z__ J__ K__ F__
Format 2: (G17)G02/03 X__ Y__ R__ F__
(G18)G02/03 X__ Z__ R__ F__
(G19)G02/03 Y__ Z__ R__ F__