14. FUNCTIONS TO SIMPLIFY
This cycle performs left–handed tapping. In the left–handed tapping
cycle, when the bottom of the hole has been reached, the spindle rotates
G74 (G98) G74 (G99)
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
Point R level
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.
Feedrate overrides are ignored during left–handed tapping. A feed hold
does not stop the machine until the return operation is completed.
Before specifying G74, use a miscellaneous function (M code) to rotate
the spindle counterclockwise.
When the G74 command and an M code are specified in the same block,
the M code is executed at the time of the first positioning operation. The
system then proceeds to the next drilling operation.
When K is used to specify the number of repeats, the M code is executed
for the first hole only; for the second and subsequent holes, the M code
is not executed.
When a tool length offset (G43, G44, or G49) is specified in the canned
cycle, the offset is applied at the time of positioning to point R.
Tapping Cycle (G74)