How to Select Insert for CNC Turning: Simple Guide

To select an insert for CNC turning, choose based on the material you are machining, the type of cut, and the insert shape and grade. Use ISO insert codes to identify the correct insert type, considering factors like chip control, wear resistance, and cutting speed.

Syntax

The selection of a CNC turning insert follows a standard code format that describes its shape, size, tolerance, and material grade.

• Insert Shape: Defines the geometry (e.g., C = 80° diamond, S = square).
• Insert Size: The length of the cutting edge in millimeters.
• Tolerance: Precision class of the insert.
• Insert Thickness: Thickness of the insert.
• Insert Type: Specifies the chipbreaker or cutting edge style.
• Material Grade: The coating and substrate suited for specific materials.

Example code: CNMG 432 where C is shape, N is clearance angle, M is tolerance, G is chipbreaker type, and 432 is size and thickness.

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Insert Code Format:
[Shape][Clearance Angle][Tolerance][Chipbreaker] [Size][Thickness][Corner Radius]

Example: CNMG 432
- C: 80° diamond shape
- N: 0° clearance angle
- M: Medium tolerance
- G: General purpose chipbreaker
- 4: 4.76 mm size
- 3: 3.18 mm thickness
- 2: 0.8 mm corner radius

Example

This example shows how to select an insert for turning mild steel with medium cutting speed and finishing operation.

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Insert Selection Example:
Material: Mild Steel (AISI 1045)
Operation: Finishing
Recommended Insert: CNMG 432-MF

Explanation:
- CNMG: 80° diamond shape, 0° clearance, medium tolerance, general chipbreaker
- 432: size and thickness
- MF: Medium Finishing grade suitable for steel

Use this insert for smooth surface finish and good tool life.

Output

Selected Insert: CNMG 432-MF
Material: Mild Steel
Operation: Finishing
Result: Smooth finish with good tool life

Common Pitfalls

• Choosing an insert with wrong shape can cause poor surface finish or tool breakage.
• Using an insert grade not suited for the material leads to fast wear or chipping.
• Ignoring chipbreaker type can cause poor chip control and machine damage.
• Not matching insert size and thickness to tool holder causes improper fit and vibration.

Always verify the insert code matches your machining needs and tool holder specifications.

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Wrong way:
Insert: SNMG 432 (Square shape for finishing)

Right way:
Insert: CNMG 432 (Diamond shape better for finishing and smooth cuts)

Quick Reference

Insert Feature	Description	Common Codes
Shape	Defines insert geometry	C (80° diamond), S (Square), T (Triangle)
Clearance Angle	Angle between insert and workpiece	N (0°), P (11°), M (7°)
Tolerance	Precision class	M (Medium), H (High)
Chipbreaker	Controls chip flow	G (General), F (Finishing), R (Roughing)
Material Grade	Insert coating and substrate	P (Steel), M (Stainless), K (Cast Iron)

Key Takeaways

Select insert shape and grade based on the material and operation type.

Use ISO insert codes to identify correct insert features and compatibility.

Match insert size and thickness to your tool holder for proper fit.

Consider chipbreaker type for effective chip control and surface finish.

Avoid common mistakes like wrong insert shape or unsuitable grade to extend tool life.