CNC Lathe Threading Program G76
Thread cutting on a CNC lathe is extremely important, and G76 is a multi-pass and widely used threading cycle. It is considered one of the precision machining operations.
The G76 cycle is considered an ideal choice for not only external but also internal finish quality threading.
With the help of the G76 threading cycle, the machine operator can produce complex threads with finish, and high accuracy, which further increases its importance in modern CNC machining.
The G76 threading cycle is used to make metric or inch threads accurately, quickly and safely. It is a simple and multi-pass threading programming cycle for cutting threads.
The greatest advantage of this cycle is that it completes the thread not in a single cut but in several light cuts, which also reduces the stress on the tool and improves the quality of the thread and reduces the risk of machine or tool breakage.
G76 One-Line Threading Cycle (Fanuc Type)
G76 threading cycle in CNC (Fanuc-style) using the single-line format with each parameter explained and a small example.
G76 X__ Z__ I__ K__ D__ A__ F__;
| X | Minor diameter (end point of the thread) |
| Z | End position of the thread |
| I | Taper |
| K | Depth of finishing pass |
| D | First pass depth |
| A | Thread angle |
| F | Thread pitch |
M20 x 2.5 metric thread from Z0 to Z-40:
G76 X18 Z-40 I0.5 K2 D0.025 A60 F2.5;X18 = Minor diameter of the thread will end at 18 mm
Z-40 = Thread length along Z-axis is 40 mm
I0.5 = Initial depth of cut per pass is 0.5 mm
K2 = Number of finishing passes (2 finishing passes)
D0.025 = Depth reduction factor for threading cycle
A60 = Thread angle is 60° (standard metric thread)
F2.5 = Thread pitch is 2.5 mm
G76 Two-Line Threading Cycle (Fanuc Type)
G76 P020060 Q100 R0.025;
G76 X18 Z-40 P1530 Q500 R0 F2.5;Line 1
This line sets the threading parameters.
P020060 = this is three pairs of digits:
02 = Number of finishing passes
00 = Thread pull-out angle (0° = straight pull-out)
60 = Thread angle (60° → standard metric / UN thread)
Q100 = Minimum depth of cut
In microns = 0.10 mm minimum cut per pass
R0.025 = Finishing allowance
0.025 mm left for the finishing passes
Line 2
This line defines the actual thread geometry.
X18 = Final (minor) diameter of the thread
For an external thread, this is the root diameter
Z-40 = End position of the thread
Thread length = 40 mm
P1530 = Thread height
In microns = 1.530 mm
This matches closely to a 2.5 mm pitch metric thread
Q500 = Depth of first cut
In microns = 0.50 mm
R0 = Taper amount
0 = straight (no taper)
F2.5 = Thread pitch
2.5 mm pitch
This is a 60° external metric thread with a 2.5 mm pitch, most likely an M20 × 2.5, cut over a 40 mm thread length.
