3 Methods of Thread Milling: Radial, Circular Arc and Tangential Cutting, Which Is the Most Practical?

In order to realize thread milling, the machine tool must have the function of three-axis linkage.

Spiral interpolation is the function of CNC machine. The tool is controlled by the machine tool to realize the spiral path.

Spiral interpolation is formed by the linkage of plane arc interpolation and linear motion perpendicular to the plane.

For example, the spiral track from point A to point B (see Fig. 1) is formed by the linkage of the plane arc interpolation motion of X-Y and the linear linear linear motion of Z axis.

For most CNC systems, this function can be realized through the following two different instructions.

  • G02: instantaneous clockwise arc interpolation command;
  • G03: counterclockwise arc interpolation command.
3 Methods of Thread Milling: Radial, Circular Arc and Tangential Cutting, Which Is the Most Practical? 1

The display of thread milling motion (see Fig. 2) is formed by the rotation of the tool itself and the spiral interpolation motion of the machine tool.

In the interpolation process of egger circle, the geometric form of the prop is used, combined with the movement of the tool moving egger pitch along the z-axis direction, to process the required thread.

Thread milling can adopt the following three cutting methods: arc cutting method, radial cutting method and tangential cutting method.

1. Arc cutting method

With this method, the cutting tool cuts in smoothly, leaving no cutting marks and no vibration, even when machining hard materials.

The programming of this method is more complicated than the radial cutting method.

It is recommended to use this method when machining precision threads.

3 Methods of Thread Milling: Radial, Circular Arc and Tangential Cutting, Which Is the Most Practical? 2
  • 1-2: fast positioning;
  • 2-3: the cutter cuts in tangentially along the arc feed, and interpolates the feed along the Z axis at the same time;
  • 3-4: 360 ° full circle thread interpolation movement, axial movement of a lead;
  • 4-5: the cutter cuts in tangentially along the arc feed, and performs interpolation movement along the Z axis at the same time;
  • 5-6: quick return.

2. Radial cutting method

This method is the simplest, but sometimes the following two situations occur:

1) Small vertical marks will be left at the cut-in and cut-out points, but the quality of the thread will not be affected.

2) When machining very hard materials, when the cutting is close to the full tooth shape, due to the increase of the contact area between the tool and the workpiece, the phenomenon of tool vibration may occur.

In order to avoid the vibration when the cut is close to the full tooth, the feed rate should be reduced to 1/3 of the spiral interpolation supply as far as possible.

3 Methods of Thread Milling: Radial, Circular Arc and Tangential Cutting, Which Is the Most Practical? 3
  • 1-2: fast positioning;
  • 2-3: the whole circle of 360 ° performs spiral interpolation movement and moves axially by one lead;
  • 3-4: radial return.

3. Tangential cutting method

This method is very simple and has the advantages of arc cutting method, but it is only applicable to the milling of external threads.

3 Methods of Thread Milling: Radial, Circular Arc and Tangential Cutting, Which Is the Most Practical? 4
  • 1-2: fast positioning;
  • 2-3:360 ° full circle makes thread interpolation movement, and the axial movement is one lead;
  • 3-4: quick return.

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