Called with many names like
G74 Left-hand tapping cycle, G74 Reverse tapping cycle, G74 Counter tapping cycle etc.
But works the way as G84 tapping cycle works.
As G84 tapping cycle is just for right hand tapping, so cnc machinists can do left-hand tapping with G74 tap cycle.
G74 Reverse Tapping Cycle Operation
Tapping with G74 tapping cycle is performed by rotating the spindle counter-clockwise. When the bottom of the hole has been reached, the spindle is rotated in the clockwise direction for retraction. This operation creates left hand threads.
G74 Tapping Cycle Format
G74 X_ Y_ Z_ R_ F_
X Y – Hole position data
Z – Z-depth (feed to Z-depth starting from R plane)
R – Position of the R plane
F – Cutting feedrate
With Rigid Tapping, the ratio between feedrate and spindle speed must be calculated for thread pitch being cut. The calculation is 1 Threads Per Inch x rpm = tapping feedrate.
F (Feed) = RPM x Pitch.
G74 Left-hand tapping cycle G-code is modal, so cancelled with G80 otherwise it will execute tapping operation on every X and/or Y move.
Use G98 and G99 for the Z position clearance location.
For more info read G84 Tapping Cycle – CNC Mill Programming