Understanding the G78 Threading Cycle in Fanuc Lathe Programming

Fanuc on doubt is the most widely used and understood cnc control.
Fanuc is used on variety of machines like mill, lathe etc.

Fanuc 21 TB

So sometimes while dealing with G-codes interesting things happen like Fanuc G code Groups (or Fanuc G code Groups Types) A, B, C.
Like a cnc machinist comes with G-code like G76 Threading cycle on one Fanuc cnc control.
But on another Fanuc control model you see G78 Threading cycle.
Mostly the working is same as G76 threading cycle behaves same as G78 threading cycle.

For a complete Fanuc G-code list with A,B,C group G-codes read Complete G Code List.

G78 Threading Cycle Format

G78 P010060 Q100 R0.05
G78 X30 Z-20 P1024 Q200 F2

First block of the G78 Threading cycle

G78 : G code for threading cycle.

P : P actually consists of multiple values which control the thread behavior,

• 01 : Number of spring passes or spring cuts or finishing cuts.
• 00 : Thread run out.
• 60 : Flank angle or Infeed angle (allowed values 0, 29, 30, 56, 60, 80).

Q : Depth of cut.
R : Depth of Finish cut

Second block of the G78 Threading cycle

G78 : G code of the threading cycle.
X (U) : The end value in x-axis.
Z (W) : The end value in z-axis.
P : Thread depth ( as radius value ).
Q : Depth of first cut.
F : Thread Pitch
R : Thread Taper

As G78 threading cycle behaves same as G76 threading cycle so you might like following articles as well.

• Internal Threading.
• External Threading.
• Taper Threading.
• Multi-Start Threading.
• CNC Programming Example.