
B-63944EN-2/02 PROGRAMMING 5.FUNCTIONS TO SIMPLIFY PROGRAMMING
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5.1.2 Left-Handed Tapping Cycle (G74)
This cycle performs left-handed tapping. In the left-handed tapping
cycle, when the bottom of the hole has been reached, the spindle
rotates clockwise.
Format
G74 X_ Y_ Z_ R_P_ F_ K_ ;
X_ Y_ : Hole position data
Z_ : The distance from point R to the bottom of the hole
R_ : The distance from the initial level to point R level
P_ : Dwell time
F_ : Cutting feedrate
K_ : Number of repeats (if required)
G74 (G98) G74 (G99)
Point R
Point Z
P
P
Spindle CW
Spindle
CCW
Initial level
Point R
Point Z
P
P
Spindle CW
Spindle
CCW
Point R level
Explanation
- Operations
Tapping is performed by turning the spindle counterclockwise.
When the bottom of the hole has been reached, the spindle is rotated
clockwise for retraction. This creates a reverse thread.
CAUTION
Feedrate overrides are ignored during left-handed
tapping. A feed hold does not stop the machine
until the return operation is completed.
- Spindle rotation
Before specifying G74, use an auxiliary function (M code) to rotate
the spindle counterclockwise.
If drilling is continuously performed with a small value specified for
the distance between the hole position and point R level or between
the initial level and point R level, the normal spindle speed may not be
reached at the start of hole cutting operation. In this case, insert a
dwell before each drilling operation with G04 to delay the operation,
without specifying the number of repeats for K. For some machines,