Ev-technologyHow-ToBeginner · 3 min read

G Code for Threading on Lathe: Syntax and Example

To perform threading on a lathe using G code, use G76 for multi-pass threading or G92 for single-pass threading cycles. These commands control the tool path to cut threads by specifying parameters like pitch, depth, and start/end points.

📐

Syntax

The common G code commands for threading on a lathe are G76 and G92. G76 is used for multi-pass threading cycles, allowing precise control over thread depth and pitch. G92 is a simpler single-pass threading cycle.

Typical G76 syntax:

G76 P Q R - Defines passes, minimum depth per pass, and retract amount.
X Z - Defines the end point of the thread.
P Q F - Defines thread pitch, total depth, and feed rate.

Typical G92 syntax:

G92 X Z F - Defines thread end point and feed rate for single pass.

gcode

G76 P3 Q0.02 R0.005
X20.0 Z-30.0
P2.0 Q0.5 F1.0

💻

Example

This example shows a multi-pass threading cycle using G76 to cut a thread with 3 passes, 2 mm pitch, and 0.5 mm total depth.

gcode

N10 G76 P3 Q0.02 R0.005
N20 X20.0 Z-30.0
N30 P2.0 Q0.5 F1.0
N40 G00 X50 Z50

Output

Tool moves to start position Threading cycle runs 3 passes cutting 0.5 mm depth total with 2 mm pitch Tool retracts to safe position

⚠️

Common Pitfalls

Common mistakes when programming threading on a lathe include:

Not setting the correct pitch or feed rate, causing poor thread quality.
Incorrect retract values leading to tool crashes or incomplete threads.
Using G92 for deep threads which may cause tool overload; prefer G76 for multi-pass control.
Forgetting to set the correct spindle speed and tool offsets before threading.

Example of wrong vs right:

gcode

Wrong:
G92 X20.0 Z-30.0 F0.1  ; Single pass too slow and deep

Right:
G76 P3 Q0.02 R0.005
X20.0 Z-30.0
P2.0 Q0.5 F1.0  ; Multi-pass with controlled depth and feed

📊

Quick Reference

Command	Description	Key Parameters
G76	Multi-pass threading cycle	P=passes, Q=min depth/pass, R=retract, X=end diameter, Z=end position, P=pitch, Q=total depth, F=feed rate
G92	Single-pass threading cycle	X=end diameter, Z=end position, F=feed rate
F	Feed rate	Defines thread pitch feed in mm/rev
S	Spindle speed	Set RPM for threading operation

✅

Key Takeaways

Use G76 for multi-pass threading to control depth and pitch precisely.

Set correct feed rate matching thread pitch to ensure quality threads.

Avoid single-pass threading (G92) for deep or complex threads to prevent tool damage.

Always verify retract values to avoid collisions during threading cycles.

Prepare spindle speed and tool offsets before starting threading operations.