Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 603)

Thread Cutting
Chapter 25
25-3
Axis feedrates - When threading, the speed of the cutting axis is
determined by the controlling spindle speed and the thread lead through
this equation:
axis feedrate = (S) / (F inches per revolution)
= (S) / (E threads per inch)
= (S)(E inches per thread)
Where : Is :
S the actual speed of the controlling spindle (programmed spindle speed times
the spindle speed override switch setting in percent)
F threads per revolution or degree depending on the current active mode
E threads per inch or inches per revolution as determined in AMP by your
system installer.
The programmer should use this equation to verify that the feedrate
resulting from the thread parameters does not exceed the maximum
allowable feedrate for the cutting axis. Otherwise an error results and
axis motion stops. This equation can also be applied to face threads and
tapered threads.
Pullout angles - During threading cycles, the control synchronizes the
moves of the X and Z axes with the spindle speed. This occasionally
may force the X axis to move quite rapidly in order to produce the
desired thread taper or pullout angles at the rates dictated by the active
spindle speed. Compounded with the fact that many machines have X
axis feedrate limits lower than those for the Z axis, the result may be
velocity limitations. This is best prevented by first executing a Feed
Check prior to actually cutting the threads and then reducing spindle
speed or changing the pullout angle where necessary.
Tapered Thread Lead - When cutting a tapered thread, the thread lead
(E- or F-word) is applied to the axis that travels the greatest distance
from the start to the end of the threading pass.
Infeed - Plunge infeed relies on a sharp tool made at the exact thread
angle that cuts on both sides of the tip as it is fed perpendicular to the
work on successive passes. On larger threads, this type of infeed may
cause vibration. In that case, angular infeed may be preferred. This
results in the tool being fed along the thread flank with each successive
pass, meaning only one side of the tip cuts. Figure 25.1 illustrates
plunge and angular infeed.