Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 602)

Thread Cutting
Chapter 25
25-2
When performing threading operations, remember:
Emergency Stop - Pressing the emergency stop during threading causes
all axes to come to a rapid stop. This likely causes damage to the part or
tool and resuming the threading moves is not possible.
<CYCLE STOP> (cycle suspend) - A cycle stop does not occur if this
button is pressed during a threading pass; instead the block executes in
this manner:
If G33, or G34 threading is being executed then axis motion continues
and cycle stop is ignored.
If G78 or G21 threading is being executed, one of two possible paths is
taken by the control. If the threading retract feature has been enabled,
the control immediately chamfers out of the thread, retracts the tool and
then returns to the start point of the threading cycle. If no threading
retract is enabled then the control continues execution until it has
completed the entire pass of the threading cycle and returned to the start
point of the move.
Overrides - During the execution of any threading pass, all feedrate
overrides are fixed at 100%.
Single Block - In single block mode the entire cycle is executed for
G21. For G78 one complete sub-cycle (including the return move to the
initial point) is performed each time cycle start is pressed. When
performing single pass threading (G33 or G34) motion stops at the end
of the threading block typically resulting in a ringing of the thread.
Dry Run - Whether or not the “dry run” and spindle speed override
functions are operable during threading is determined by the system
installer’s PAL program.
Radius/Diameter Mode - The control performs threading in either
radius or diameter modes. Radius/Diameter mode only affects the
controls interpretation of the X parameter.
Start point - Due to axis acceleration and other machine dynamics, the
threading cycles should be programmed such that the axes have room to
attain speed prior to contacting the workpiece. Failure to do so may
result in the initial thread lead being incorrect.
Controlling spindle - On systems with multiple spindles, the
controlling spindle (selected with G12) is the synchronized spindle used
for thread cutting. The controlling spindle RPM, in conjunction with
the programmed thread lead (F or E), determine the threading axis
feedrate.
25.1
Considerations for Thread
Cutting