Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 609)

Thread Cutting
Chapter 25
25-9
The programmed lead remains in effect until another thread lead value is
programmed, the control is reset, or an M02 or M30 end of program block
is executed.
For tapered threads, the thread lead (determined by the F- or E-word) is
applied along the axis that travels the greatest distance when cutting the
thread. See Figure 25.6.
Figure 25.6
Lead Designation for Tapered Thread
X
Z
Z
X
If Z < X then thread lead is along X
If Z ³ X then thread lead is along Z
1/E, E or F
1/E, E or F
When the X-axis is used as the thread lead axis for E or F, program thread
leads as radial values.