How to Choose Positive and Negative Turning Inserts | LiZhou ISO Turning Tool Code Analysis

In CNC turning and conventional lathe machining, the selection and application of turning inserts are closely linked to cutting control, machining efficiency, and tool life. Today, we will explore the key considerations regarding turning inserts. ISO What do these standards signify? Today, Lizhou will guide you through a systematic approach to selecting turning inserts, covering key aspects such as insert geometry, shape, dimensions, and cutting-edge design, to help you gain a thorough understanding of turning inserts. 

Table of Contents

1. What is a turning tool?
2. Why is it important to understand turning tools? ISO Code? 
3. Lizhou ISO A comprehensive analysis of the code? 
4. How to select positive- and negative-rake turning inserts? 
5. Selecting the Appropriate Turning Insert 
6. Frequently Asked Questions 

I. What is a turning tool?

Turning tools are indexable cutting tools mounted on a lathe tool post, serving as standardized, indexable cutting inserts for machining metals and hard materials. In this process, the workpiece rotates while the insert remains stationary and feeds axially; the cutting edge removes material to achieve the desired surface finish, ultimately balancing cutting control with machining performance. 

II. Why It Is Necessary to Understand Turning Tools ISO Code?

ISO The code serves as the “identity identifier” for turning inserts, and it is essential to understand these codes both during the machining process and when making purchases. So why is it important for us to know these codes?

1. Precise selection: Based on ISO With the code, we can quickly match blade shape parameters and so on.
2. Enhancing Machining Performance: Selecting the Right Insert Enables Superior Cutting Control 
3. General communication: as a global standard, ISO Code serves as a common language between suppliers and engineers, thereby minimizing information bias. 

III. Lizhou ISO A comprehensive analysis of the code?

Using Lizhou’s classic model CNMG120408-MA For example , Bit-by-bit parsing ISO Code meaning:

The first letter of the turning insert code denotes the insert geometry, which directly affects cutting strength and machining accessibility. Each company has its own material grade specifications; for example, Lizhou. CNMG120408 The letters and numbers on indexable turning inserts represent the insert’s core specifications in sequence:

C The letter stands for: blade shape, which is 35 Diamond-shaped blade

N The letter represents: the back rake angle of the cutting blade, which is 7 °Positive back rake angle and sharp cutting edge effectively reduce cutting resistance.

M Letter designation: Blade manufacturing tolerance grade

G Letters represent: clamping method and chip-breaker type.

12 The number represents the inscribed circle diameter of the blade, approximately 16mm

04 The number represents the blade thickness, approximately 4.76mm

First: Blade Shape

All turning inserts have a unique ISO The code may be partially modified by the company based on its own design, and it includes both letters and numbers that each carry specific meanings.

Only by looking ISO With the code, you can determine the insert’s geometry, back rake angle, manufacturer, and thickness.

Below are the turning inserts. CNMG120408-MA Example:

Below are the shape options for turning inserts, as well as ISO Graphical correspondence of the code:

Second: Back Angle Code

The second letter in the turning insert designation represents the insert’s back rake angle, for example: CNMG120408 of the “ N “This determines the cutting resistance and the sharpness of the cutting edge.”

N ：0 °Rear rake angle (negative insert), double-sided usable, high edge strength, suitable for light cutting

C ：7 °Rear rake angle (positive insert), low cutting resistance, and sharp cutting edge make it the first choice for finish machining of slender shafts.

Other common back angles B （ 5 °) \D （ 15 °) \E （ 20 °) and so on, suitable for different precision and cutting requirements.

The back rake angle of a turning insert is critical for achieving efficient machining, as it influences chip formation, tool life, and other factors. By understanding the effects of the back rake angle, selecting an appropriate value can significantly enhance machining performance.

Please review the various back angles of Lizhou turning inserts and their ISO Correspondence of codes

Third: Tolerance Grade

CNMG120408 in the ” M ” Represents dimensional tolerance, which affects tool fit accuracy and repeatable positioning; tolerance specifications are denoted by letters. A to U Indicates that each letter corresponds to a specific dimensional tolerance.

The tolerance options and their… are listed below. ISO Correspondence of the code:

Fourth: Cross-Section Type 

CNMG Fourth in the middle ” G ” Represents the blade clamping method and chip-breaker geometry: G Features a center hole and chip-breaker groove design, compatible with double-clamp tool holders for stable chip evacuation. 

The cross-sectional view highlights differences in blade design, such as mounting holes, countersink holes, and special structural features, which determine the clamping method used for the blade.

Below are the options for cross-sectional types, as well as ISO Correspondence of the code:

Fifth: Numbers 12 What does it mean?

The two-digit number represents the inscribed circle diameter of the insert, which determines the overall size of the insert:

12 : indicates the diameter of the inscribed circle 12.7 mm, It is compatible with turning inserts of corresponding specifications and is a common size for general machining. The larger the size, the greater the insert rigidity, making it suitable for heavy-duty machining with large depths of cut. 

Below are typical example nominal dimensions for the inscribed circle of standard turning inserts:

Sixth: Number 04 What does it mean?

These two digits represent the blade thickness:

04 : indicates that the thickness of this blade is 4.76 mm, The thickness is consistent, making it suitable for most conventional cutting conditions: the greater the thickness, the better the impact resistance, ideal for rough machining; the thinner the thickness, the sharper the cutting edge, ideal for finish machining.

Below are typical examples of standard thicknesses for turning inserts:

Seventh: Number 08 What does it represent?

These two digits in the turning insert designation represent the nose radius, which affects surface finish and cutting-edge strength.

08 : indicates that the nose radius of this insert is 0.8mm, Suitable for semi-finishing and rough turning, capable of achieving high surface finish; single-edge design is relatively weak. 

Below are typical examples of the nose radius sizes for Lizhou turning inserts:

Eighth: This symbol represents different brand markings and chip-breaker geometries. 

Master of Arts : Indicates the type of chip breaker groove , The cutting control performance is determined by the geometry of the groove: roughing geometries are optimized for large depths of cut, while finishing geometries are optimized for small cuts; the Lizhou grade adheres to this principle. ISO Material grade.

IV. How to Select Positive and Negative Corner Inserts

Positive-tilt insert: ISO The second digit in the code is usually C , indicating the back angle 7 °, the insert has a clearance angle and a single-sided cutting edge, making it prone to vibration; it is suitable for finish machining and is used as an internal-bore turning tool. 

Negative-tilt insert: ISO The second digit in the code is usually N , indicating the back angle 0 °. The blade is symmetrical top and bottom, can be used on both sides, offers high rigidity, is ideal for rough machining, and is highly durable. 

The above outlines the distinction between positive-rake and negative-rake inserts; you can select the insert that best suits your machining conditions. 

V. Selecting the Appropriate Turning Insert

Lizhou recommends that you follow these three principles when selecting turning inserts:

1. Appropriate operating conditions: Clearly determine whether you are performing roughing, semi-finishing, or finishing. For rough turning, negative-rake inserts are recommended; for finish turning, positive-rake inserts are recommended. Select the appropriate turning insert based on your specific machining conditions.
2. Material selection: Each enterprise has material requirements when selecting turning inserts; for stainless steel, the following is recommended: PVC For coating grades, specialized grades can be selected for machining high-temperature materials such as cast iron. 
3. Code verification: Through the above, we have understood ISO The code verifies parameters such as geometry, dimensions, and back rake angle to ensure full compatibility with the tool holder and machining requirements. 

I am confident that, as long as you select your inserts based on the three principles outlined above and then machine them using the appropriate parameters, you will be able to choose turning inserts that are perfectly suited to your needs.

VI. Frequently Asked Questions

1. What is the recommended entry-level cutting insert for general turning applications?

Recommend Li Zhou CNMG120408 Series of negative-rake inserts, suitable for machining a wide range of materials.

2. What causes poor surface finish after precision turning and polishing? 

This may be due to an excessively large radius at the cutting edge; you can opt for a insert model with a smaller diameter, such as VCMT1103 and VCMT1604, We can prioritize VCMT1103, Poor surface finish can also result from unstable tool holding or dull cutting edges.

3. How to Select the Appropriate Turning Insert 

Selecting Turning Inserts Correctly: Choose the Material—Select the Geometry and Rake Angle—Match the Appropriate Grade and Coating—Perform a Verification ISO Code 

4. How can work hardening in stainless steel be prevented? 

Machining stainless steel requires the use of dedicated turning inserts to avoid low-speed frictional cutting; select stainless-steel-specific grades with appropriate toughness, and maintain stable cutting parameters.

There is no one-size-fits-all approach to selecting turning inserts; the key is to choose the insert that best suits your specific application and machining conditions. LIZHOU Cemented Carbide can provide tailored insert solutions based on your workpiece material, machine tool capabilities, and cutting requirements, helping you achieve efficient, high-quality, and cost-effective machining.