Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 365)

Axis Motion
Chapter 14
14-7
Example 14.5
Arc Programmed Using Radius
Arc 1 Arc 2
center angle less than center angle greater than
180 degrees 180 degrees
G90G02X25.Z40.R18.F.1; G90G02X25.Z40.R-18.F.1;
Figure 14.5
Results of An Arc Programmed with Radius Command, Example 14.5
R-18 start
point
Arc 1
R18
end point
Arc 2
Z
40
25
X
Important: Any axis that is not specified when programming a circle
remains at its current axis position value. This results in the arc’s end point
having the same coordinate value as the start point of the arc for that axis.
If you do not specify the end point of the arc, or if the end point is the same
as the start point, two results are possible:
if you use I and/or K to program the arc center, the control cuts a full
circle
if you use R to program the radius of the arc, no arc is made (the control
does not move either axis)