Threading cycle

Threading is one of the most common operations performed on CNC lathes. Whether you’re cutting external or internal threads, using a threading cycle helps automate the process, reduce programming time, and ensure consistent thread quality. In this blog post, we’ll explore what a threading cycle is and provide syntax examples for three of the most widely used CNC control systems:

• Fanuc
• Siemens (Sinumerik)
• Heidenhain

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What Is a Threading Cycle?

A threading cycle is a canned cycle that automates the motion required to cut a thread. It allows the programmer to define key parameters such as:

• Thread pitch
• Depth of cut
• Number of passes
• Start and end positions
• Feed rate

Instead of manually writing each pass with G-code, a single line (or block) of code can initiate the entire threading operation.

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1. Fanuc Control – G92 Threading Cycle

Fanuc controls are widely used in the industry, especially in Asia and North America. The G92 command is commonly used for simple straight threading cycles.

📌 Syntax:

G92 X(U)__ Z(W)__ F__ ;

• X or U: Final thread diameter (absolute/incremental)
• Z or W: End position along the Z-axis
• F: Thread pitch (feed per revolution)

✅ Example – External Thread Cutting:

G97 S500 M03 ;        (Constant spindle speed)
G00 X30.0 Z2.0 ;      (Rapid move to start point)
G92 X28.5 Z-20.0 F1.5 ; (First threading pass)
X28.0              ; Second pass
X27.6              ; Third pass
X27.4              ; Final pass
G00 X100.0 Z100.0 ;   (Retract tool)
M30 ;               (End program)

💡 Tip: Multiple passes are programmed by changing only the X value while keeping Z, F, and other parameters the same.

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2. Siemens Sinumerik – CYCLE97 for Threading cycle

Siemens Sinumerik controls are popular in Europe and use more descriptive commands. The CYCLE97 function is used for longitudinal threading.

📌 Syntax:

CYCLE97 (PTP, PITCH, THREAD_DEPTH, FIRST_CUT_DEPTH, ANGLE, ...)

✅ Example – Internal Thread Cutting:

M03 S600 ;                (Spindle on clockwise)
G00 X16.0 Z2.0 ;          (Position to start point)
CYCLE97 (Z-20, 1.5, 0.9, 0.3, 60) ; 
; Parameters:
; Z-20 = Thread length
; 1.5 = Pitch
; 0.9 = Total thread depth
; 0.3 = First cut depth
; 60 = Thread angle
G00 X100 Z100 ;          (Retract)
M30 ;                    (Program end)

⚙️ Note: Siemens often uses modal drilling/turning cycles that handle multiple passes automatically based on parameters.

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3. Heidenhain – L93 for Threading cycle

Heidenhain controls are known for their conversational programming interface but also support standard G-code. The L93 subroutine is typically used for threading operations.

📌 Syntax (in conversational mode):

THREADING
Thread Diameter: ___
Thread Length: ___
Pitch: ___
Start Position Z: ___
Number of Passes: ___

✅ Example – G-code Equivalent:

BLK FORM 0.1 Z+0 ;     (Workpiece definition)
TOOL CALL 1 Z S3000 ;  (Tool selection and spindle speed)
L93 X30 Z-20 F1.5 A60 ; (Threading cycle)
; Where:
; X = Major diameter
; Z = Thread length
; F = Pitch
; A = Thread angle
M30 ;                  (End of program)

💡 Tip: Heidenhain’s L93 handles both internal and external threads depending on how X is defined.

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Comparison Summary

Feature	Fanuc (G92)	Siemens (CYCLE97)	Heidenhain (L93)
Command Type	Modal G-code	Canned cycle	Subroutine / Conversational
Pitch Input	F parameter	Parameter list	F parameter
Thread Angle	Manual setup	Defined in parameters	A parameter
Multiple Passes	Repeat line with X	Built-in logic	Predefined number of passes
Ease of Use	Simple, manual	Flexible, automated	Very user-friendly

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Conclusion

Understanding how to use threading cycles across different CNC control systems is essential for efficient machining. While the basic concept remains the same — cutting threads with multiple passes — the way you input data varies significantly between Fanuc, Siemens, and Heidenhain.

Whether you’re working with G-code or a conversational interface, mastering these cycles will save you time, reduce errors, and improve the quality of your threaded parts.

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Want More?

If you found this helpful, check out our other posts on:

• CNC Drilling Cycles Explained
• Turning canned cycle
• Thread standards

Stay tuned for more tips and tutorials on CNC programming and machining best practices!

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📌 Got questions about threading cycles or want to share your favorite syntax tricks? Drop a comment below!