Cycle Syntax
T1212 M06;
G97 S400 M03;
G76 P040060 Q100 R0.2;
G76 X18.2 Z-18.0 P180 Q160 F1.5;
G00 X25.0 Z10.0;
G97 S400 M03;
G76 P040060 Q100 R0.2;
G76 X18.2 Z-18.0 P180 Q160 F1.5;
G00 X25.0 Z10.0;
Parameter Explanation
P(1) – Number of spring passes (to improve finish and repeatability)
P(2) – Chamfer angle at thread runout
P(3) – Thread angle (e.g., 60° for metric)
Q (1st line) – Minimum cut amount
R (1st line) – Finish allowance
X – Core (minor) diameter of thread
Z – Thread end position (in Z-axis)
P (2nd line) – Thread depth (in microns)
Q (2nd line) – First cut depth (in microns)
R (2nd line) – Taper amount (optional, for taper threads)
F – Thread pitch (mm per revolution)
Taper Thread R Value Explanation
When machining a taper thread using G76, an additional R parameter in the second G76 line is used to indicate the taper depth across the Z movement.
- Formula:
R = 0.031 × (Thread Length + Z position value ) - Use
−Rvalue for OD taper threads - Use
+Rvalue for ID taper threads
This accounts for the taper angle, typically 1°47′24″ (1.789°), and is required for proper thread depth control along the taper.
Threading Example – M20 × 2.5
Given: M20 thread, Pitch = 2.5mm
- Major diameter: 20.0 mm
- Minor diameter (X): = 20 − 2 × 0.649 × P = ~17.55 mm
- Thread depth (P): 0.649 × P = 1.6225 mm = 1623 microns
- First cut depth (Q): ~10% of thread depth = 0.15 mm = 150 microns
- Finish allowance (R): 0.2 mm
G76 Block:
G76 P020060 Q100 R0.2; G76 X17.55 Z-25.0 P1623 Q150 F2.5;
⚠️ Note:
🔸 G76 two-line method gives greater control and is supported in most FANUC controllers
🔹 'P' in 1st line is 3 combined values (spring pass, chamfer, angle)
🔸 All values in microns unless specified (e.g., P/Q)
❗ For taper threads, always calculate the R value correctly using the taper thread formula
🔸 G76 two-line method gives greater control and is supported in most FANUC controllers
🔹 'P' in 1st line is 3 combined values (spring pass, chamfer, angle)
🔸 All values in microns unless specified (e.g., P/Q)
❗ For taper threads, always calculate the R value correctly using the taper thread formula