G35 CNC Code | Circular Threading CW | Turning

English CNC Wiki
1

G35 CNC Code: Mastering Clockwise Circular Threading on Lathes

Introduction:

CNC turning offers a wide range of threading capabilities, from simple straight threads to complex variable lead threads. The G35 G-code unlocks a specialized threading technique: clockwise circular threading. This guide provides a comprehensive understanding of G35 circular threading, explaining its purpose, parameters, applications, and how it differs from other threading methods. This knowledge is valuable for both novice and experienced CNC machinists.

1. What is G35 Clockwise Circular Threading?

G35 circular threading is a CNC lathe operation where the cutting tool moves in a clockwise circular arc while simultaneously cutting a thread. This is distinct from linear threading (G32, G33, G76) where the tool moves in a straight line along the Z-axis. G35 allows you to create threads that follow a curved path, opening up possibilities for unique component designs.

Key Concepts:

  • Circular Path: The tool follows a defined circular arc, unlike the straight-line path of standard threading.
  • Clockwise Direction: The tool moves in a clockwise direction around the defined arc (when viewed from the positive Z-direction). This is important for tool orientation and clearance.
  • Constant Pitch: While the path is circular, the thread pitch (distance between adjacent threads) remains constant. This is a key difference from G34 (variable lead threading).
  • Arc Center: The center point of the circular.

2. G35 Syntax and Parameters

The basic syntax for the G35 command can vary slightly depending on the specific CNC controller, but a common format is:

G35 X[End X] Z[End Z] I[X Offset] K[Z Offset] F[Feed Rate]

or

G35 X[End X] Z[End Z] R[Radius] F[Feed Rate]

Let’s break down each parameter:

  • G35: The G-code initiating clockwise circular threading.
  • X[End X]: The X-axis coordinate of the end point of the circular thread.
  • Z[End Z]: The Z-axis coordinate of the end point of the circular thread.
  • I[X Offset]: The X-axis offset from the starting point of the arc to the center of the arc.
  • K[Z Offset]: The Z-axis offset from the starting point of the arc to the center of the arc.
  • R[Radius]: Radius value of the circular path.(Some controls use this parameter instead of I and K.)
  • F[Feed Rate]: The feed rate, which, in the context of threading, is effectively the thread pitch. This is because the feed rate is synchronized with the spindle rotation.

Important Notes:

  • I and K vs. R: Some controllers use I and K to define the arc center, while others use R for the radius. Consult your machine’s programming manual to determine the correct format. If using I and K, they are incremental distances from the starting point.
  • Thread Pitch: F defines thread pitch.
  • Incremental vs. Absolute: The I and K values are typically incremental from the starting point of the arc. This means they represent the change in X and Z, not absolute coordinates.
  • Starting Point: You must position the tool at the correct starting point of the arc before executing the G35 command (using G00 or G01).

3. G35 vs. Other Threading Commands

Understanding the differences between G35 and other threading G-codes is vital:

  • G35 vs. G32/G33 (Linear Threading):

    • G32/G33: Create straight threads along the Z-axis.
    • G35: Creates threads that follow a circular path.

  • G35 vs. G34 (Variable Lead Threading):

    • G34: Creates straight threads with a changing pitch.
    • G35: Creates circular threads with a constant pitch.

  • G35 vs. G36 (Counterclockwise Circular Threading):

    • G35: Clockwise circular threading.
    • G36: Counterclockwise circular threading. The choice depends on the desired thread direction and tool orientation.

  • G35 vs. G76:

    • G35 offers less automation.
    • G35 is for special applications.

Key Differences Summarized:

Feature G32/G33 G34 G35 G36
Path Linear Linear Circular (CW) Circular (CCW)
Pitch Constant Variable Constant Constant
Direction N/A N/A Clockwise Counterclockwise

4. Applications of G35 Circular Threading

G35 is used for creating threads on curved surfaces or in situations where a straight thread is not feasible:

  • Special Fasteners: Bolts or nuts with curved thread paths for unique locking or sealing mechanisms.
  • Threaded Inserts: For curved housings or components.
  • Medical Devices: Components with curved channels or features requiring threads.
  • Aerospace Components: Parts with complex geometries requiring precisely placed threads.
  • Ornamental Threads: Decorative threads on curved surfaces.
  • Pipe Threads: Used in plumbing.
  • Curved Motion Transfer Mechanisms: Creating a circular path.

5. Programming Example: G35 External Circular Thread

Let’s create an external circular thread using G35:

N10 G90 G21 ; Absolute programming, metric units
N20 T0101    ; Select tool 1, offset 1
N30 G97 S500 M03 ; Constant spindle speed, 500 RPM, spindle on
N40 G00 X20.0 Z5.0 ; Rapid to the starting position

; --- Circular Threading ---
N50 G00 X15.0 Z0.0 ; Move to the thread start point (X is smaller than the final diameter)
N60 G35 X25.0 Z-10.0 I0.0 K-10.0 F1.5 ; Circular thread (CW), end X25, end Z-10, arc center is at Z-10 relative to start, pitch = 1.5mm
N70 G00 X20.0    ; Rapid retract in X
N80 G00 Z5.0     ; Rapid return to safe Z position

N90 M30       ; Program end

Explanation:

  1. Setup (N10-N30): Standard setup: programming mode, units, tool, spindle.
  2. Initial Positioning (N40): Move to a safe position.
  3. Thread Start Point (N50): Move to the starting point of the circular thread. This is crucial. The X value should be smaller than the final thread diameter to allow for the cutting tool to engage the material.
  4. G35 Command (N60):
  • G35: Initiates clockwise circular threading.
  • X25.0 Z-10.0: The end point of the circular thread.
  • I0.0 K-10.0: The arc center is 0.0 mm in X and -10.0 mm in Z relative to the starting point. This means the center of the circle is at X15.0, Z-10.0 in absolute coordinates.
  • F1.5: The thread pitch is 1.5 mm.
  1. Retract (N70-N80): Retract the tool and return to a safe position.
  2. Program End (N90): End the program.

Important Considerations for this Example:

  • Arc Center: The I and K values define the arc center relative to the starting point. Carefully calculate these values based on your desired thread geometry.
  • Multiple Passes: For most threads, you’ll likely need multiple passes, gradually increasing the X diameter until the full thread depth is reached. This example shows only one pass.
  • R Parameter: If your machine uses the R parameter instead of I and K parameters, your code should be like below.

N60 G35 X25.0 Z-10.0 R10.0 F1.5

6. Best Practices for G35 Circular Threading

  • Accurate Calculations: Double-check all calculations for the arc center (I, K or R), end point (X, Z), and thread pitch (F). Errors will result in incorrect thread geometry.
  • Correct Tool Orientation: Ensure the threading tool is properly oriented for clockwise cutting. This may involve using a different toolholder or insert compared to standard threading.
  • Rigid Setup: Minimize vibration and deflection by using a rigid setup (workpiece and tool holding).
  • Appropriate Cutting Fluid: Use a suitable cutting fluid to improve chip evacuation, surface finish, and tool life.
  • Simulation: Always simulate the program before running it on the machine to check for errors and potential collisions. CAM software is highly recommended for G35 programming.
  • Gradual Depth Increments: Use multiple passes with small depth increments, especially for harder materials or larger threads.
  • Spindle Speed: Choose an appropriate spindle speed for the material and thread size.
  • Machine Compatibility: Verify that your CNC controller supports G35.

7. Troubleshooting Common G35 Problems

  • Incorrect Thread Geometry:
    • Cause: Incorrect I, K, R, X, or Z values; incorrect starting point; tool not properly oriented.
    • Solution: Double-check all calculations, verify tool orientation, use simulation.
  • Rough Thread Finish:
    • Cause: Dull tool, incorrect spindle speed, insufficient cutting fluid, excessive depth of cut.
    • Solution: Sharpen or replace the tool, adjust cutting parameters, use appropriate cutting fluid.
  • Tool Breakage:
    • Cause: Excessive cutting forces, incorrect tool geometry, material buildup, incorrect arc parameters.
    • Solution: Reduce depth of cut, use a sharper tool, ensure proper chip evacuation, double-check arc calculations.
  • Alarm/Error Message:
    • Cause: Syntax error, unsupported G-code, incorrect parameter values.
    • Solution: Consult your machine’s programming manual, check for typos, verify parameter limits.

8. Conclusion: Expanding Your Threading Capabilities

The G35 clockwise circular threading command provides CNC machinists with a powerful tool for creating threads on curved surfaces and in specialized applications. By understanding its syntax, parameters, best practices, and troubleshooting tips, you can significantly expand your CNC turning capabilities and produce high-quality, complex threaded components.