Mastering the G76 Threading Cycle: Full Control of Passes and Depth of Cut

Fanuc cnc control is no-doubt the widely used cnc machine control and the most used Fanuc canned cycle is G76 Threading cycle.

G76 threading cycle comes with lot and lot of parameters, no-doubt difficult to learn and remember, but if you are a true cnc machinist then remembering these threading cycle parameters is not a difficult job.

G76 threading cycle gives a cnc machinist the most flexibility for threading operation.

This article will tell you how you can change following values with G76 threading cycle parameters

• Depth of cut for First pass
• Depth of cut for normal passes
• Depth of cut for Last pass
• Control number of Spring passes

How to Fully Control G76 Threading Cycle Number of Pass and Depth of Cut

CNC programmers/machinists might find other articles about G76 threading cycle like
G76 Threading Cycle Explained CNC Fanuc G76 Threading Cycle.
G76 Taper Threading Tapered Threading with Fanuc G76 Threading Cycle.
G76 Multi-start Threading Multi Start Threads with Fanuc G76 Threading Cycle.
G76 External Threading External Thread Cutting with G76 Threading Cycle on Fanuc 21i 18i 16i CNC.
G76 Internal Threading Internal Threading on Fanuc 21i 18i 16i with G76 Threading Cycle.
G76 Controlling Infeed Angle Controlling Threading Infeed Angle with Fanuc G76 Threading Cycle.

G76 Threading Cycle Tips for Thread Pass Control

The below cnc program code is the typical format which a cnc machinist use while programming threading with G76 threading cycle.

N5 G76 P010060 Q100 R0.05
N6 G76 X30 Z-20 P1024 Q200 F2

Depth of First Pass

With Q parameter in second-block of G76 threading cycle you can change the threading depth of First-pass of threading operation.
In the above code Q200 value is given so while threading our tool will take 0.2(mm or inch) deep cut for the first pass.

Depth of Each Pass

For remaining passes depth of cut G76 use First-block Q parameter which is given above as Q100 (0.1 mm or inch).

Depth of Last Pass or Finish Cut

Last of Finish cut is also programmed with G76 as in above code First-block R parameter is given R0.05 (0.05 mm or inch)

Number of Spring Passes

Once the threading cycle has completed the Finish-cut (R parameter in first-block) you can program tool to take extra passes (spring pass) on the same depth for multiple times (to smooth or finish thread surface).
Spring passes can be controlled through P parameter in First-block of G76 threading cycle

P : P actually control three different values which control the thread behavior,

• 01 : Number of spring passes or spring cuts.
• 00 : Thread run out at 45 degree
• 60 : Flank angle or Infeed angle

For spring pass control only first pair value is used of P parameter, as above 01 is given, the tool will take one extra pass, you can change this value according to your requirements.