Rockwell Automation 8520 9/Series CNC Lathe - Manual (Page 584)

Compounding Turning Routines
Chapter 24
24-20
In Figure 24.14, the contour blocks for this routine must define all motions
that would cut the workpiece finished shape. The first block of the contour
blocks must be the tool path from the start point to the point where the
initial roughing pass begins. The first block of the contour blocks may not
be a rapid move (G00).
Important: The blocks preceding the G74 roughing block must have
positioned the cutting tool to a location above the part (start point in the
above figure) from which it can safely move to begin the roughing passes.
If cutting a Case 1 contour, the first of the contour blocks must command Z
axis motion only (no X axis motion). If cutting a Case 2 contour, the first
of the contour blocks must command both an X and Z axis motion.
The G74 roughing routine activates the Tool Tip Radius Compensation
(TTRC) function regardless of whether it was active prior to the roughing
routine. If TTRC was not active, the roughing routine uses the tool tip
radius data of the previously programmed T-word. At the end of the
roughing routine, TTRC is cancelled unless it was active prior to the
roughing routine.
In Example 24.4, the workpiece contour blocks are blocks N11 - N14.
Example 24.4
Typical G74 Block Followed by Blocks Defining Final Contour
N005 G74 P11 Q14 U.2 W.2 D1.2 F10. S210;
.
.
N010 M30;
N011 Z25;
N012 X55 Z40;
N013 X40 Z65;
N014 X30 Z75;
The finish allowance words (U and W) in the G74 block are a signed value
dependant on the workpiece contours. Figure 24.15 illustrates this with the
workpiece contour blocks generating the motions from point A to C.