Lathe cutting tools: definition, classification and core technology details

Lathe cutting tools are key tools used for cutting and forming workpieces on lathes in metal processing. Through the relative movement of the tool and the workpiece, the excess material is removed, and the required geometric shape, dimensional accuracy and surface quality are finally formed. Its performance directly affects the processing efficiency, cost and part quality. The following is a comprehensive analysis from multiple dimensions such as structure, material, type, and application.

1. The essential definition and functional positioning of lathe cutting tools

Lathe cutting tools are the core executive components in the field of precision machining. The essence of its technology lies in converting the workpiece blank into a precision part with specific geometric features through a controllable material removal process.

This type of tool is installed on the lathe tool holder or turret. The workpiece is driven to move by the rotation of the spindle. The tool is fed along the coordinate axis, and the sharp cutting edge is used to plow, shear or extrude the workpiece surface, and finally achieve the processing goals of dimensional accuracy (IT6-IT12), shape accuracy (such as roundness 0.001-0.1mm) and surface roughness (Ra0.1-12.5μm).

Its core functions include: material removal efficiency control (removal volume of 10-1000cm³ per minute), processing accuracy assurance (micron-level error control), surface quality optimization (through edge finishing technology) and special structure processing (such as complex features such as threads and molded surfaces).

2. Basic structure and function of lathe cutting tools

(1) Tool body (tool bar)

Material: usually alloy steel (such as 40Cr) or cemented carbide, with high rigidity and vibration resistance. Function: fix the blade, transmit cutting force, and some tool bars have integrated coolant channels.

Standard specifications: ISO tool bar models (such as DCLNR/L, SDUCR/L) correspond to different installation angles and sizes.

(2) Blade (cutting head)

Material: cemented carbide, ceramic, CBN, PCD, etc. (see Part 4 for details).

Geometric features: parameters such as rake angle, back angle, and edge inclination angle determine cutting performance.

Indexable design: Most modern blades are polygonal (triangular, diamond, etc.), and a single blade contains multiple cutting edges. After wear, it can be rotated and used.

(3) Chip breaker groove

Type: open (for cast iron), closed (for steel), corrugated groove (special for stainless steel).

Function: Control chip shape (C-shaped chips, short spiral chips) to prevent entanglement with workpieces or tools.

(4) Clamping mechanism

Lever type: Quick blade replacement, suitable for high-speed processing.

Screw type: High stability, used for heavy cutting conditions.

3. Core classification and application scenarios of lathe cutting tools

Classification Criteria	Type	Typical Applications
Machining Location	External turning tool	Turning external diameters and end faces of shaft-type parts
	Internal turning tool (boring tool)	Machining holes with diameter ≥ Φ3mm, accuracy up to IT7 grade
	Cut-off tool (grooving tool)	Grooving and cutting off, tool width 0.5–10mm
	Thread turning tool	Machining metric, inch, and trapezoidal threads, pitch 0.5–6mm
Structural Form	Solid tool	Micro-part machining (diameter < Φ1mm)
	Welded tool	Low-cost rough machining, non-replaceable inserts
	Indexable tools (mainstream)	Used in over 90% of modern lathes, high efficiency and quick tool change
Cutting Direction	Right-hand tool	Feeds from right to left when the spindle rotates clockwise
	Left-hand tool	Special clamping requirements or machining in confined spaces

4. Material types and selection guide for lathe cutting tools

Material Type	Hardness (HV)	Heat Resistance (℃)	Applications	Limitations
High-Speed Steel (HSS)	800–900	600	Low-speed machining for complex shapes (e.g., form tools)	Poor wear resistance, short tool life
Cemented Carbide	1400–1800	800–1000	General turning (steel, cast iron, stainless steel)	Weak impact resistance, sensitive to thermal shocks
Ceramic (Al₂O₃)	2000–2200	1200	High-speed finish turning of cast iron and hardened steel	Brittle, unsuitable for interrupted cutting
CBN (Cubic Boron Nitride)	3000–4500	1400	Machining hardened steel (>HRC45) and powder metallurgy	High cost, requires rigid tool clamping
PCD (Polycrystalline Diamond)	7000–8000	700 (oxidation limit)	Ultra-precision machining of non-ferrous metals (aluminum, copper)	Cannot machine ferrous metals, sensitive to heat

Note: Coating technology (such as TiAlN, TiCN) can further improve the heat resistance and life of cemented carbide tools.

5. Geometric parameter analysis of lathe cutting tools

(1) Rake angle (γ₀)

Definition: The angle between the front face of the tool and the base surface.

Influence:

Positive rake angle (+γ₀): Light cutting, but low edge strength (suitable for finishing).

Negative rake angle (-γ₀): Strong impact resistance, high cutting force (used for roughing or hard materials).

Recommended value: +5°~+15° for steel, -5°~+5° for cast iron.

(2) Back angle (α₀)

Function: Reduce the friction between the back face of the tool and the workpiece.

Typical range: 6°~12°, small value for hard materials and large value for soft materials.

(3) Main deflection angle (κᵣ)

Definition: The angle between the main cutting edge and the feed direction.

Selection principle:

45°: General processing, taking into account radial/axial forces.

90°: Suitable for step shaft processing, small radial force.

<30°: Roughing with large feed, but easy to cause vibration.

(4) Blade inclination angle (λₛ)

Positive blade inclination angle: Chips flow to the machined surface, protecting the tool tip (for fine turning).

Negative blade inclination angle: Chips flow to the surface to be machined, improving the edge strength (for rough turning).

6. Wear mechanism and life management of lathe cutting tools

(1) Wear type

Flanking face wear (VB value): Normal wear form, VB＞0.3mm requires tool change.

Crescent wear: Pit formed on the front face due to high temperature diffusion, common in high-speed steel tools.

Breaking edge: Edge fragmentation caused by intermittent cutting or material impurities.

(2) Life prediction model

Taylor formula: VTn=C

V: Cutting speed (m/min)

T: Tool life (min)

n: Material index (n≈0.25 for carbide processing steel parts)

C: Constant (matching with tool/workpiece material)

Modern method: AI life prediction based on cutting force and temperature signals, error <10%.

(3) Measures to extend tool life

Optimize cooling: High-pressure cooling (pressure > 5MPa) can reduce tool temperature by more than 200℃.

Control cutting depth: The back cutting amount should not exceed 60% of the blade length.

Avoid idling: The tool rotation should be stopped during non-cutting periods.

7. Selection and maintenance guide for lathe cutting tools

(1) Three-step selection method

STEP 1: Determine the processing material - stainless steel, aluminum alloy, hardened steel, etc. correspond to different blade materials.

STEP 2: Determine the process type - select negative rake angle blades for rough turning and positive rake angle blades for fine turning.

STEP 3: Match machine tool power - avoid using blades with large back cutting amount for low-power machines (<10kW).

(2) Installation accuracy requirements

Tool tip height error: It needs to be aligned with the spindle centerline, with a deviation of ≤0.02mm.

Radial runout: The runout of the blade after installation is <0.01mm (check with a micrometer).

(3) Daily maintenance points

Cleaning: Clean the chips and oil in the tool groove after each tool change.

Rust prevention: Apply anti-rust oil during long-term storage, and the humidity should be less than 60%.

Regular inspection: Cracks in the tool bar need to be detected by magnetic particle inspection to prevent breakage accidents.

8. Summary

Lathe cutting tools are the "sharp blades" of mechanical processing. Their selection and use require comprehensive material science, mechanical analysis and process experience. From the manual sharpening of traditional high-speed steel tools, to the intelligent application of modern indexable tools, to the nano-level processing of super-hard material tools, every breakthrough pushes the boundaries of precision manufacturing. Only by mastering the core technology of tools can we achieve "softness overcoming hardness" and be at ease in the field of metal cutting.