Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 604)

Thread Cutting
Chapter 25
25-4
Figure 25.1
Angular versus Plunge Infeed
Cutting tool Cutting tool
Angular Infeed Plunge Infeed
The G78 threading pass allows the selection of different infeed types by
programming a P-word. If you use any of the other threading methods,
it is necessary to insert a small Z move to generate an angular feed.
Form Cut Threading - The auto threading cycles (G21 and G78)
assume a sharp triangular tool. If you use a shaped-tip tool, the tool
loading is affected. Specifically, the first cut is loaded slightly less than
successive cuts. Though generally insignificant, if this is a concern, we
suggest that the initial cut depth be compromised as necessary to ensure
that the tool is not overloaded on successive passes.
Using Thread Chamfer
The thread chamfer feature, enabled in PAL, cuts a chamfer at the end of a
thread cutting pass. When the feature is activated, the control
automatically cuts a chamfer at the end of each thread cutting pass to
assure the tool is fully out of the thread before it is retracted.
This feature prevents the “ring” at the end of the thread that typically
occurs when the control stops threading motion to retract the tool. This
ring occurs when the threading axis reaches the endpoint of the thread and
decelerates before executing the retract move. Typically spindle RPM
does not compensate for this deceleration of the threading axis thus
causing a ring at the end of the thread.
Both the thread retract and thread chamfer use the same values (set in
AMP) for the pullout distance “r” and pullout angle “a” of the chamfer.
“r” is entered as the number of threads to be chamfered, “a” is entered as
the angle of the chamfer in degrees measured from the same axis as the
thread lead.
25.2
Chamfering Your Threads