Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 580)

Compounding Turning Routines
Chapter 24
24-16
Figure 24.12
Stock Removal in G74 Rough Facing
Shape after roughing
and final pass
Workpiece finished
shape
Z
Finishing allowance
Start point
Tool paths determined automatically
X
The G74 block has a P and Q parameter that call the sequence numbers
(N-words) of the first and last blocks defining the final contour to be cut
into the workpiece. This set of blocks may be located anywhere after the
calling block (even after an end of program command), as long as the
calling block is in the same program as the set of contour defining blocks.
This means that contour blocks can not be called from a subprogram or a
macro unless the calling block is in that subprogram or macro.
The control handles two different cases of the G74 routine and
automatically recognizes them and adapts the tool path accordingly.
Case 1:
A Case 1 G74 rough facing routine is defined when the workpiece contour
has no pockets. The following constraints must be met in order to
successfully perform a Case 1 rough facing routine:
The first block of the contour program must command motion in only
the Z axis. No X axis motion is permitted in the first block of the
contour program.
The contour either continuously increases or continuously decreases in
both the X and Z axis except for the first block of the contour program.
The first contour point in the contour blocks must be closer to the
spindle centerline than the last contour point.