Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 643)

Milling Fixed Cycles
Chapter 26
26-11
Important: When programming a G74 tapping cycle, consider this:
The programmer or operator must start spindle rotation.
Override usage- the control ignores the feedrate override switch and
clamps override at 100 percent.
During tapping the feedrate override switch, and the feedhold feature
are both disabled. Cycle stop is not acknowledged until the end of the
return operation.
Figure 26.5
G74: Left-Hand Tapping Cycle
Cutting feed
Rapid feed
R point level
initial point
level
R
Z
Hole bottom
Spindle rotation direction is
reversed at hole bottom
1
2
3
4
5
6
7
In the G74 left-hand tapping cycle, the control moves the axes in the
following manner:
1. The tool rapids to the initial point level above the hole location.
2. The threading tool then rapids to the R point level, slows to the
programmed cutting feedrate and begins the tapping operation.
3. During the tapping operation, the control infeeds the threading tool to
the depth and at the feedrate programmed in the tapping cycle.