Smithy CNC Mills - Manual (Page 18)

2.2 G1: Linear Motion at Feed Rate
For linear motion at feed rate (for cutting or not), program G1 X- Y- Z- A- B- C-,
where all the axis words are optional, except that at least one must be used.
The G1 is optional if the current motion mode is G1. This will produce coordinat-
ed linear motion to the destination point at the current feed rate (or slower
if the machine will not go that fast).
It is an error if:
* all axis words are omitted.
If cutter radius compensation is active, the motion will differ from the above;
see Chapter [cha:Cutter-Radius-Compensation]. If G53 is programmed on the
same line, the motion will also differ; see Section [sub:G53:-Move-in].
2.3 G2, G3: Arc at Feed Rate
A circular or helical arc is specified using either G2 (clockwise arc) or G3 (coun-
terclockwise arc). The axis of the circle or helix must be parallel to the X, Y, or
Z-axis of the machine coordinate system. The axis (or, equivalently, the plane
perpendicular to the axis) is selected with G17 (Z-axis, XY-plane), G18 (Y-axis,
XZ-plane), or G19 (X-axis, YZ-plane). If the arc is circular, it lies in a plane paral-
lel to the selected plane.
If a line of RS274/NGC code makes an arc and includes rotational axis motion,
the rotational axes turn at a constant rate so that the rotational motion starts
and finishes when the XYZ motion starts and finishes. Lines of this sort are
hardly ever programmed.
If cutter radius compensation is active, the motion will differ from what is
described here. See Chapter [cha:Cutter-Radius-Compensation].
Two formats are allowed for specifying an arc. We will call these the center for-
mat and the radius format. In both formats the G2 or G3 is optional if it is the
current motion mode.
2.3.1 Radius format arcs
In the radius format, the coordinates of the end point of the arc in the selected
plane are specified along with the radius of the arc. Program G2 X- Y- Z- A- B-
C- R- (or use G3 instead of G2). R is the radius. The axis words are all optional
except that at least one of the two words for the axes in the selected plane
SmithyCNC Programmer’s Reference Manual: G Codes 2-3