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The Difference Between Positive And Negative Angle Of CNC Cutting Tools


In CNC (Computer Numerical Control) machining, cutting tools are used to shape and remove material from a workpiece. The terms “positive angle” and “negative angle” refer to the orientation and geometry of the cutting edge of the tool. During the CNC machining process, the operator needs to make selections and adjustments based on factors such as processing materials and required surface quality. In today’s article, we discuss the difference between positive angle and negative angle of cutting tools.

The Positive Angle For CNC Cutting Tool


In CNC machining, the term “positive angle” typically refers to the rake angle of a cutting tool. The rake angle is the angle between the cutting edge and a reference plane perpendicular to the tool axis. It determines the orientation of the cutting edge with respect to the direction of tool rotation.

For a positive angle, the cutting edge is inclined in a positive direction relative to the tool axis. In other words, the cutting edge faces in the direction of tool rotation. This configuration is commonly used for cutting tools used in machining soft materials such as aluminum, brass, plastics, and non-ferrous metals.

The specific positive angle for a cutting tool can vary depending on the application, tool type, and material being machined. It is typically measured in degrees and can range from a few degrees to a larger positive value. The positive angle helps to create a sharp cutting action, reduce cutting forces, and facilitate efficient chip evacuation.

The positive angle is just one of the many factors to consider when selecting a cutting tool for a specific machining operation. Other factors such as tool material, tool geometry, cutting parameters, and workpiece material properties also play a crucial role in achieving optimal machining performance. Manufacturers and tool suppliers provide recommendations and guidelines for selecting the appropriate positive angle based on these considerations.

The Negative Angle Of A CNC Cutting Tool


In CNC machining, the term “negative angle” is not commonly used to describe cutting tools. Instead, the concept of a negative rake angle is often discussed.

The rake angle refers to the angle between the cutting edge and a reference plane perpendicular to the tool axis. A negative rake angle means that the cutting edge is inclined in a negative direction relative to the tool axis. In other words, the cutting edge faces opposite to the direction of tool rotation.

A negative rake angle is typically used for cutting tools that are intended for machining hard materials such as stainless steel, hardened steels, and cast iron. The negative angle provides increased tool strength and toughness, allowing the tool to withstand higher cutting forces associated with these harder materials. It also helps to improve the tool’s ability to shear the material and remove chips efficiently.

It’s worth noting that the specific value of the negative rake angle can vary depending on the tool type, application, and material being machined. Different cutting tools, such as indexable inserts for turning or milling, may have their own recommended negative rake angles.

A negative rake angle is typically employed for machining hard materials and provides increased tool strength and chip evacuation capabilities.

The Difference Between Positive Angle And Negative Angle


The main difference between a positive angle and a negative angle in the context of cutting tools lies in the orientation and geometry of the cutting edge. Here’s a breakdown of the differences:

Positive Angle

  • Cutting Edge Orientation: The cutting edge faces in the direction of tool rotation.
  • Rake Angle: The rake angle, which is the angle between the cutting edge and a reference plane perpendicular to the tool axis, is positive.
  • Material Compatibility: Positive angle tools are generally used for machining soft materials like aluminum, brass, and plastics.
  • Cutting Action: Positive angle tools provide a sharp cutting action, resulting in reduced cutting forces and improved chip evacuation.
  • Examples: High-speed steel (HSS) end mills, solid carbide end mills, and drills are examples of positive angle tools.

Negative Angle

  • Cutting Edge Orientation: The cutting edge faces opposite to the direction of tool rotation.
  • Rake Angle: The rake angle is negative, meaning the cutting edge is inclined in a negative direction relative to the tool axis.
  • Material Compatibility: Negative angle tools are commonly used for machining hard materials such as stainless steel, hardened steels, and cast iron.
  • Tool Strength: Negative angle tools offer increased tool strength and toughness, allowing them to withstand higher cutting forces associated with hard materials.
  • Cutting Action: Negative angle tools are often used in heavy roughing applications to remove material quickly.
  • Examples: Indexable inserts for turning, milling, and boring operations are examples of negative angle tools.

It’s important to consider factors such as the material being machined, the specific machining operation, cutting parameters, and desired outcomes when selecting between positive and negative angle tools. Tool manufacturers and suppliers provide guidelines and recommendations for tool selection based on these factors to optimize machining performance and tool life.

Similarities Between Positive Rake Angle And Negative Rake Angle


While positive rake angle and negative rake angle differ in their orientations and applications, they do share some similarities. Here are a few similarities between positive rake angle and negative rake angle:

1.Chip Evacuation

Both positive and negative rake angles can contribute to improved chip evacuation during machining. By providing a cutting edge orientation that promotes chip formation and removal, both types of rake angles help prevent chip clogging and promote efficient material removal.

2.Cutting Force Reduction

Both positive and negative rake angles can help reduce cutting forces during machining operations. By optimizing the cutting edge geometry and orientation, both angles can contribute to smoother cutting action and reduced forces required to shear the material.

3.Surface Finish

Both rake angles can influence the surface finish of the machined part. While positive rake angle tools are typically used for softer materials, they can still contribute to achieving a smooth surface finish by minimizing the cutting forces and reducing the likelihood of built-up edge formation. Negative rake angle tools, commonly employed for hard materials, can also provide a good surface finish due to their stability and ability to withstand higher cutting forces.

4.Tool Life

Both positive and negative rake angles can impact tool life. By optimizing the cutting edge geometry and orientation, both angles can help distribute cutting forces more effectively, reducing tool wear and extending tool life. The specific effect on tool life will vary depending on the material being machined, cutting parameters, and tool characteristics.

That the specific effects and outcomes can vary depending on the machining context, material being machined, and tool geometry. The selection of positive or negative rake angle tools should be based on the specific requirements of the machining operation and the characteristics of the workpiece material.

The Comparison Chart Of Positive Rake Angle VS Negative Rake Angle


Certainly! Here’s a table comparing positive rake angle and negative rake angle in the context of cutting tools:

AspectPositive Rake AngleNegative Rake Angle
Cutting Edge OrientationFaces in the direction of tool rotationFaces opposite to the direction of tool rotation
Rake AnglePositiveNegative
Material CompatibilitySoft materials such as aluminum, brass, plastics, non-ferrous metalsHard materials such as stainless steel, hardened steels, cast iron
Cutting ActionSharp cutting action, reduced cutting forces, improved chip evacuationIncreased tool strength, efficient chip evacuation
ExamplesHigh-speed steel (HSS) end mills, solid carbide end mills, drillsIndexable inserts for turning, milling, boring operations
Chip EvacuationImproved chip evacuationImproved chip evacuation
Cutting Force ReductionReduces cutting forcesReduces cutting forces
Surface FinishCan contribute to a smooth surface finishCan contribute to a smooth surface finish
Tool LifeCan extend tool lifeCan extend tool life

That this table provides a general overview of the characteristics and applications of positive rake angle and negative rake angle. It’s important to consider specific machining requirements, material properties, and tool selection guidelines from manufacturers when choosing between positive and negative rake angles for a particular machining operation.

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