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Cutting Tools

Jan 30, 2025

Turning inserts are small, replaceable cutting tools used in machining to shape workpieces on a lathe or turning CNC machine. Made from materials like carbide and ceramics, they withstand high temperatures and wear. These inserts ensure precise, efficient, and cost-effective material removal, improving productivity and surface quality. Their versatility allows them to be used for various operations and materials, making them indispensable in modern manufacturing. This article will help you answer the question: what are turning inserts?

Understanding the Types of Turning Inserts and Their Uses

Turning inserts are essential tools in CNC machining, each designed for specific applications to enhance precision and efficiency. Here are the common types of turning inserts and their purposes:

General Purpose Turning Inserts. This category includes universal inserts designed for semi-finishing and medium-duty turning operations, primarily used for machining the outer diameter (OD) of parts. The material to be machined is not limited and depends on the selected geometry (chip breaker) and grade.
Finishing Inserts. Designed for finishing operations, these inserts provide high-quality surface finishes. They are used when precision and smoothness are critical, such as in the final stages of CNC machining.
Roughing Inserts. Roughing inserts are used for removing large amounts of material quickly. They are ideal for the initial stages of machining, where the focus is on material removal rather than surface finish.
Threading Inserts. These inserts are specialized for cutting threads on workpieces. They ensure precise and accurate thread profiles, which are essential in applications where threaded components are needed.
Grooving Inserts. Grooving inserts are used to create grooves or channels in a workpiece. They are essential for applications that require precise grooves for sealing rings, snap rings, or other components. Grooving inserts could be for OD, ID and also face turning operations.
Parting Inserts. Parting inserts are designed for cutting off (parting) sections of a workpiece. They provide clean cuts and are essential in operations where parts need to be separated from the main workpiece.
Profiling Inserts. These inserts are used for creating complex shapes and profiles on a workpiece. They are ideal for applications that require detailed contouring and shaping.

Each turning cnc insert type is engineered to perform specific tasks, ensuring optimal performance and efficiency in various machining operations. By selecting the right insert for the job, machinists can achieve higher precision, better surface quality, and increased productivity.

The geometry of Cutting Inserts

Turning Insert Geometry Overview

Inserts are primarily categorized into positive and negative geometries:

Negative Inserts

Double-sided/Single-sided
High edge strength
Zero relief angle
First choice for external turning
Suitable for heavy cutting conditions

Positive Inserts

Low cutting forces
Relief angle present
First choice for boring and machining thin parts

Both positive and negative inserts are further divided into different shapes.The shape of the insert should be selected based on the accessibility of the cutting tool’s approach angle.

Insert Shapes (Arranged by decreasing nose angle):

R - Round (360°)
S - Square (90°)
C - Rhombic (80°, e.g., CNMG, CCMT)
W - Multi-edged (80°, e.g., WNMG)
T - Triangular (60°, e.g., TNMG)
D - Rhombic (55°, e.g., DNMG, DCMT)
V - Rhombic (35°, e.g., VNMG, VBMT)

Strength vs. Versatility

Larger nose angles provide higher cutting edge strength, while smaller angles improve edge accessibility, operational versatility, and reduce power consumption. The choice of shape depends on various factors, summarized in the table below.

What Is Important to Know When Choosing an Insert

When selecting the shape of a turning insert, several critical factors must be considered. Each shape offers unique advantages based on the application requirements, including roughing, finishing, vibration tendency, and accessibility.

1. Roughing (Strength)

Roughing requires strong cutting edges to handle high forces. Inserts with larger nose angles excel here:

R (Round) and S (Square): Best for roughing due to their strength and edge durability.
C (Rhombic): Versatile for roughing with good strength and reliability.
W (Multi-edged): Moderately suitable for roughing; less robust than R or S shapes.

2. Light Roughing/Semi-Finishing

A balance of strength and sharpness is needed for light roughing and semi-finishing:

C (Rhombic): Ideal, balancing strength and versatility.
W (Multi-edged): Effective for semi-finishing, offering more edges for diverse use.
T (Triangular) and D (55° Rhombic): Suitable when moderate edge strength suffices.

3. Finishing

Finishing demands precision and sharpness with minimal cutting forces:

V (35° Rhombic), (Triangular) and (55° Rhombic): Excellent for finishing tasks.
C (Rhombic): Can be used effectively for general finishing.

4. Vibration Tendency

Reducing vibrations requires stability and consistent contact:

R (Round): Best for minimizing vibrations due to its continuous cutting edge.
C (Rhombic) and W (Multi-edged): Good vibration resistance in less stable conditions.
T (Triangular), D (55° Rhombic): Moderate performance under vibration.

5. Longitudinal Turning

For turning along the workpiece axis:

C (Rhombic): Versatile for longitudinal turning.
T (Triangular) and D (55° Rhombic): Commonly used for such operations.
R (Round): Limited to less precise longitudinal turning.
V (35° Rhombic): Suitable for delicate or intricate turning.

6. Profiling

Profiling involves creating detailed contours and shapes:

V (35° Rhombic): Excellent for profiling due to its sharp edges and precision.
T (Triangular) and D (55° Rhombic): Good for profiling with moderate edge accessibility.
C (Rhombic): Versatile but less precise for detailed profiles.

7. Facing

For machining flat surfaces:

T (Triangular), D (55° Rhombic), and V (35° Rhombic): Perform well in facing operations.
C (Rhombic): Suitable for general-purpose facing.
R (Round): Can be used for facing but lacks precision.

8. Operational Versatility

Versatility is key for operations requiring multiple tasks:

C (Rhombic): Highly versatile for a variety of applications.
W (Multi-edged): Good for general versatility.
T (Triangular) and D (55° Rhombic): Suitable for moderate versatility.
V (35° Rhombic): Less versatile but precise.

9. Limited Machine Power

For machines with low power, sharp edges with minimal cutting resistance are ideal:

V (35° Rhombic) and T (Triangular): Best choices due to low cutting forces.
D (55° Rhombic) and C (Rhombic): Perform moderately well.

10. Hard Material

Hard materials require inserts with durable cutting edges:

C (Rhombic): Versatile for machining hard materials.
R (Round) and S (Square): Performs well in hard material cutting.
T (Triangular) and D (55° Rhombic): Effective with reduced durability.

11. Interrupted Machining

Interrupted cuts demand inserts with high impact resistance:

R (Round): Best for interrupted cuts due to its robust edges.
S (Square): Performs well under interruptions.
C (Rhombic): Versatile but less durable than R or S.
W (Multi-edged): Moderately suitable.

12. Large Approach Angle

For operations requiring wide approach angles:

R (Round) and S (Square): Best suited for large angles due to robust edge designs.
C (Rhombic) and W (Multi-edged): Perform well in moderate angles.

13. Small Approach Angle

For narrow approach angles and confined spaces:

V (35° Rhombic): Best choice for small angles due to its sharpness and accessibility.
D (55° Rhombic): Suitable for moderate accessibility.

The choice of insert shape depends on the specific operation requirements. Shapes like C (Rhombic, 80°), e.g. CNMG are versatile for most applications, while V (35° Rhombic) excels in precision tasks. R (Round) and S (Square) dominate strength-focused operations.

Tips for Choosing an Insert

Understand the specific machining operation (e.g., roughing, finishing, threading) to choose an insert that meets the requirements.
Determine the material (e.g., steel, aluminum, cast iron) to select an insert that is compatible and effective for the job.
Match the insert shape and size with the tool holder and the specific cutting needs to ensure precision and stability.
Opt for the appropriate insert material (e.g., carbide, ceramic, CBN) based on the machining conditions and desired durability.
Follow ISO standards to ensure the insert meets quality and consistency benchmarks, providing reliable performance.
Seek advice from the tool manufacturer to understand the best insert options for your specific application.
Test different inserts and fine-tune your selection to achieve the best balance of performance, precision, and cost-efficiency in your machining operations.

Turning inserts are crucial components in modern CNC machining, offering versatility and precision for a variety of tasks. From general-purpose and finishing inserts to specialized threading and grooving inserts, each type is designed to meet specific machining requirements. By understanding the different types and their uses, machinists can select the most suitable insert for their needs, ensuring optimal performance, improved surface quality, and increased productivity. Adhering to ISO standards, consulting with tool manufacturers, and experimenting with various inserts will further enhance the efficiency and effectiveness of machining operations.