Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 605)

Thread Cutting
Chapter 25
25-5
Important: This feature may only be used with the G78 or G21 threading
cycle. It is ignored if a G33 or G34 threading pass is being made.
Using Thread Retract
Enabled in PAL, thread retract lets you interrupt a thread cutting operation
without damaging the thread by pressing <CYCLE STOP>. When the
operation is interrupted, the control automatically performs a retract (by
cutting a chamfer) out of the thread to prevent damage to the thread due to
ringing. Once free of the thread the control retracts the tool and returns it
to the start point. Also, program execution stops at this point.
If you attempt to interrupt the thread cutting operation without thread
retract active, the control does not interrupt the operation until the end of
the currently executing threading pass.
Thread Chamfer and Thread Retract Parameters
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.
Figure 25.2
Ringing occurs when retracting from thread without using thread
chamfer or thread retract.
Ringing from no chamfer when cutting
tool is retracted out of thread.
Smooth exit from thread when cham-
fer is made, no ringing at end of
thread. Root depth slowly decreases.
Number of
threads
for chamfer (r)
Pullout
angle (a)