Lathe Cutting Tool Angle Selection Principle

When cutting metal, the tool cuts into the workpiece, and the tool angle is an important parameter used to determine the geometry of the cutting part of the tool.

1. The composition of the cutting part of the turning tool

The cutting part of a turning tool, commonly used in machining processes like lathe operations, typically consists of several key components:

●Tool Material: The material used for the cutting part can vary depending on the application. High-speed steel (HSS), carbide, ceramic, and cubic boron nitride (CBN) are common materials. Each material has its own properties that make it suitable for specific cutting tasks.

●Insert: In many modern turning tools, the cutting edge is not directly part of the tool body but is instead a separate insert that can be replaced when it becomes dull or damaged. Inserts are typically made of carbide or other hard materials and come in various shapes and sizes to accommodate different cutting operations.

●Cutting Edge Geometry: The cutting edge geometry, including its shape, angle, and relief, is crucial for achieving the desired cutting action and surface finish. Common cutting edge shapes include square, round, diamond, and triangle, each suitable for different types of cuts.

● Rake face The surface on which the chips flow on the tool.

● Main flank The surface on the tool that opposes and interacts with the machined surface on the workpiece is called the main flank.

● Secondary flank The surface on the tool that opposes and interacts with the machined surface on the workpiece is called the secondary flank.

● Main cutting edge The intersection of the rake face of the tool and the main flank face is called the main cutting edge.

● Minor cutting edge The intersection of the rake face and the minor flank of the tool is called the minor cutting edge.

●Tool nose The intersection of the main cutting edge and the minor cutting edge is called the tool nose. The tool tip is actually a small curve or straight line, which is called the rounding tip and the chamfering tip.

2. Auxiliary plane for measuring the cutting angle of the turning tool

Reference Plane: The reference plane serves as a baseline for measuring cutting angles. It is typically a flat surface perpendicular to the spindle axis of the lathe or machining center.

Tool Setting: The cutting tool is positioned on the reference plane, with the tool tip touching the surface. This ensures that the tool is aligned perpendicular to the spindle axis and provides a consistent starting point for angle measurements.

Angle Measurement: Various tools can be used to measure the cutting angle relative to the reference plane. These may include angle gauges, protractors, or specialized angle measurement instruments.

Cutting Edge Alignment: The cutting edge of the tool is aligned with the reference plane during measurement. This allows for accurate determination of the rake angle, clearance angle, and other cutting edge angles.

Adjustment: If necessary, adjustments can be made to the tool position or orientation to achieve the desired cutting angles. This may involve changing tool inserts, adjusting tool holders, or repositioning the tool relative to the workpiece.

In order to determine and measure the geometric angle of the turning tool, it is necessary to select three auxiliary planes as the reference. These three auxiliary planes are the cutting plane, the base plane and the orthogonal plane.

● Cutting Plane - A plane cut to a selected point on the main cutting edge and perpendicular to the bottom plane of the shank.

● Base Plane - The plane passing through a selected point of the main cutting edge and parallel to the underside of the shank.

● Orthogonal plane - a plane perpendicular to the cutting plane and perpendicular to the base plane.

It can be seen that these three coordinate planes are perpendicular to each other, forming a space rectangular coordinate system.

3. Main geometric angles and selection of turning tools

● Principle of selection of front angle (γ0 )

The size of the rake angle mainly solves the contradiction between the firmness and sharpness of the cutter head. Therefore, the rake angle should be selected first according to the hardness of the processing material. The hardness of the processed material is high, and the rake angle takes a small value, and vice versa. Secondly, the size of the rake angle should be considered according to the processing properties. The rake angle should take a small value during rough machining and a large value during finishing. The rake angle is generally selected between -5° and 25°.

Usually, the rake angle (γ0) is not pre-made when making the turning tool, but the rake angle is obtained by sharpening the chip flute on the turning tool. The chip flute is also called a chip breaker. Its function is great to break the chips without entanglement; control the outflow direction of the chips and maintain the accuracy of the machined surface; reduce the cutting resistance and prolong the tool life.

● Principle of selection of clearance angle (α0 )

Consider first the processing properties. When finishing, the clearance angle takes a large value, and when roughing, the clearance angle takes a small value. Secondly, consider the hardness of the processed material. If the hardness of the processed material is high, the main relief angle should take a small value to enhance the firmness of the cutter head; otherwise, the relief angle should take a small value. The clearance angle cannot be zero or negative, and is generally selected between 6° and 12°.

● Selection principle of main declination angle (Kr )

First, consider the rigidity of the turning process system composed of lathes, fixtures and tools. If the rigidity of the system is good, the leading angle should be taken as a small value, which is beneficial to improve the service life of the turning tool, improve heat dissipation conditions and surface roughness. Secondly, the geometry of the workpiece should be considered. When machining steps, the main declination angle should be 90°, and the main declination angle should be 60° for workpieces cut in the middle. The main declination angle is generally between 30° and 90°, and the most commonly used are 45°, 75°, and 90°.

● Selection principle of secondary declination (Kr’ )

First of all, consider the sufficient rigidity of the turning tool, the workpiece and the clamp to reduce the secondary declination angle; otherwise, a larger value should be taken; secondly, considering the processing properties, the secondary declination angle can be 10° to 15° during finishing, and 10° to 15° during rough machining. , the secondary declination angle can be about 5°.

● Selection principle of edge inclination angle (λS)

It mainly depends on the processing properties. During rough machining, the workpiece has a large impact on the turning tool, and λS ≤ 0°. When finishing, the impact force of the workpiece on the turning tool is small, and λS ≥ 0°; usually λS = 0°. The inclination angle of the blade is generally selected between -10° and 5°.

Workpiece Material: Different materials require different cutting tool angles. For example, softer materials like aluminum may require sharper cutting angles, while harder materials like steel may need more obtuse angles.