Smithy CNC Mills - Manual (Page 20)

instead of G2). The axis words are all optional except that at least one of X and Y
must be used. I and J are the offsets from the current location (in the X and Y
directions, respectively) of the center of the circle. I and J are optional except
that at least one of the two must be used. It is an error if:
* X and Y are both omitted
* or I and J are both omitted.
When the XZ-plane is selected, program G2 X- Y- Z- A- B- C- I- K- (or use G3
instead of G2). The axis words are all optional except that at least one of X and Z
must be used. I and K are the offsets from the current location (in the X and Z
directions, respectively) of the center of the circle. I and K are optional except that
at least one of the two must be used. It is an error if:
* X and Z are both omitted,
* or I and K are both omitted.
When the YZ-plane is selected, program G2 X- Y- Z- A- B- C- J- K- (or use
G3instead of G2). The axis words are all optional except that at least one of Y and
Z must be used. J and K are the offsets from the current location (in the Y and Z
directions, respectively) of the center of the circle. J and K are optional except that
at least one of the two must be used. It is an error if:
* Y and Z are both omitted
* or J and K are both omitted.
Here is an example of a center format command to mill an arc: G17 G2 x10 y16 i3
j4 z9.
That means to make a clockwise (as viewed from the positive z-axis) circular or hel-
ical arc whose axis is parallel to the Z-axis, ending where X=10, Y=16, and Z=9,
with its center offset in the X direction by 3 units from the current X location and
offset in the Y direction by 4 units from the current Y location. If the current loca-
tion has X=7, Y=7 at the outset, the center will be at X=10, Y=11. If the starting
value of Z is 9, this is a circular arc; otherwise it is a helical arc. The radius of this
arc would be 5.
In the center format, the radius of the arc is not specified, but it may be found eas-
ily as the distance from the center of the circle to either the current
point or the end point of the arc.
SmithyCNC Programmer’s Reference Manual: G Codes 2-5