Cutting Tools - A small introduction

Whether it’s building machines, repair work in trades or manufacturing precision components, cutting tools are used almost everywhere. Turning tools, milling tools, drilling tools, and grinding tools are used whenever material needs to be removed in the form of chips. This article explains the types of cutting tools available and what matters when using them.

What is machining?

Machining is a manufacturing process in which material is removed from a workpiece by mechanical action in the form of chips to achieve the desired shape, surface, or dimensional accuracy. These methods can be classified into the category of separating production methods according to DIN 8580. These processes can be used to manufacture complex components with tightest tolerances economically.

Key machining procedures include:

What is the role of machining tools in industrial manufacturing?

In industrial manufacturing, machining tools play a critical role. They enable the production of components with complex geometries, tight tolerances and high-quality surfaces. Selecting the right tool will significantly affect production speed, quality and cost-effectiveness.

Main Groups of Cutting Tools

There are a wide range of cutting tools for a wide variety of applications. In principle, they can be divided into the following main groups:

Turning Tools

Turning tools are used in turning, a process in which the workpiece rotates and the tool creates the desired shape.

Typical turning tools include:

• Tool holders (outside and inside)
• Grooving/parting holders
• Threading holders
• Drill bits

Milling Tools

During milling, the tool rotates while the workpiece is guided.

Typical milling tools include:

• End mills
• Special cutters
• Face mills
• Slot mills
• Form cutters
• Disc cutters

Drilling tools

Drilling tools are used to create cylindrical inner surfaces.

Typical drilling tools include:

• Drill bits, e.g. for creating cylindrical holes.
• Step drills, e.g. for producing several hole diameters in one operation.
• Countersinking tools for making conical or cylinder counterbores, such as for flush countersinking screw heads.

Grinding tools

Grinding tools are made of bonded abrasive grain and are used for finishing surfaces (see also our article on the selection of surfaces).

Typical grinding tools include:

• Grinding wheels
• Grinding belts
• Honing tools (for fine machining as a final step after turning or milling)

Materials and coatings for cutting tools

The performance of cutting tools depends on the cutting material and the coating. Common materials include (☐ = color coding):

The following table provides an overview of the main application groups for cutting materials according to DIN ISO 513.

The following table provides an overview of the suitability of the main application group according to DIN ISO 513 for the HRC strength classes.

( suitable / not suitable )

Coatings such as RiN, TiAIN, AlCrN or DLC increase tool life, reduce friction and improve heat conductivity. Selection is based on material, coolant, and cutting parameters.

Tool geometry and chip formation

The geometry of a cutting tool determines the cutting performance and the quality of the machining. It provides controlled chip flow and high quality surfaces.

Key parameters include:

• Cutting angle/wedge angle: affects chip formation and cutting force.
  • A large angle increases stability and is suitable for heavy cuts.
  • A small angle improves sharpness and precision.
• rake angle: controls chip flow.
  • A positive rake angle reduces cutting forces and is suitable for soft materials.
  • With a negative rake angle, the cutting surface is tilted away from the cutting direction, creating a stronger cutting edge. (for harder and brittle materials)
• Clearance angle: prevents friction between the tool and workpiece.
  • A small clearance angle increases the stability of the cutting edge in rough machining.
  • A larger clearance angle reduces friction and heat buildup in fine cuts.

Selection Criteria for Cutting Tools

Several properties play a central role in the selection of cutting tools: Workpiece material, desired surface finish, machine performance, cost, tool life, geometry, and coating. Hard materials, for example, require high heat-resistant cutting materials such as tungsten carbide or PVD-coated HSS, while softer materials can be efficiently machined even with simpler steels. Cheaper tools are easier to recondition, but typically achieve lower tool life and cutting performance compared to coated tungsten carbide or CBN tools.

The selected geometry, e.g. rake and clearance angle, significantly influences chip formation, cutting forces and thus ultimately surface finish and dimensional accuracy. Higher machine performance and cutting speeds create stronger forces, requiring robust cutting geometries and coatings with high heat resistance.

Here’s a quick decision-making guide for cutting tools by hardness:

• Soft materials: HSS or uncoated tungsten carbide with large rake angle, high cutting speed, low cutting forces.
• Medium-hard materials: coated tungsten carbide (e.g. TiAlN), robust geometry, good balance of tool life and precision.
• Hard materials (greater than 60 HRC): CBN, PCD or fine-grain tungsten carbide with stable cutting edge, low cutting speed, high wear resistance required.

Machine compatibility: Toolholder Requirements

There are various standardized toolholder systems such as steep taper SK (ISO 7388), hollow shank taper HSK (DIN 69893), metric taper (ME), Weldon holder and Morse taper. HSK toolholders feature high static and dynamic rigidity and precise radial positioning, which enables accurate and repeatable machining, even at high speeds. Thanks to their short changeover times, integrated coolant supply and optional coding, they are ideal for automated high-speed processes with the highest demands for precision and efficiency. The hollow shank taper is considered a standard interface. Morse taper reamers also offer high precision with precisely crafted taper angles for precise toolholders and are versatile in a wide range of machine tools and industries. The Weldon mount is traditionally used in milling applications and ensures torque resistance and secure tool holding.

Tool wear and tool life

Tools are subject to various wear mechanisms during machining, which significantly affect their service life and machining quality. The most common types of wear include:

• Flank wear: Abrasion on the tool flank due to friction
• Crater wear: Material removal on the rake surface due to high temperatures and diffusion
• Cutting edge breakage: Sudden cutting edge breakout due to overload or vibration
• Plastic deformation: Permanent deformation of the cutting edge due to overheating

Tool wear can be detected early by visual inspection, degradation of surface quality or by monitoring cutting forces and process noise. To increase tool life, optimally tuned cutting data, efficient cooling and regular re-grinding are crucial. The selection of wear-resistant coatings (e.g. TiAlN) and a low-vibration machine environment also contribute to extending tool life.

Influence of cutting fluids

During machining, heat is generated, which on the one hand can lead to tool wear, but on the other hand can also lead to thermal deformation of the workpiece itself. The use of cutting fluids (KSS) counteracts this through efficient cooling and lubrication. At the same time, chips that arise during processing are rinsed away and the work area is cleaned.

Depending on the function, the coolants also differ: There are pure cutting oils that have a particularly high lubricity, but are, for example, less suitable for cooling. Cooling lubricants that can be mixed with water in turn have a high cooling effect, but achieve an equally good lubricating effect with regular stirring. Synthetic coolants must be dissolved in water and are transparent, which helps in observing the machining process. Which coolant is used depends on the manufacturing process applied. If high working temperatures prevail with easily machined workpieces, a coolant with a high cooling characteristic is recommended. For hard-to-machine materials and moderate speeds, lubrication is a priority. The addition of additives, e.g. corrosion inhibitors, optimizes the coolant for a variety of applications.

Typical Machining Errors

A key problem in machining is the insufficient balance between material selection and subsequent machining steps. Often, attention is paid only to machinability without considering how the material behaves in other processes such as welding or forming. Typical sources of error include shortened tool life caused by inhomogeneous material batches, hard phases, or incorrect cutting conditions. Also, problems with shape and dimensional tolerances often occur when the starting material has excessive out-of-roundness or bow deviations. Another risk is the lack of homogeneity of the material. Unequally distributed inclusions make chip formation difficult and lead to unstable processes. Internal stresses in the material can lead to unwanted deformation during machining, which jeopardizes the dimensional accuracy. While heat treatment can reduce these stresses, it can degrade other properties such as machinability. Insufficient surface finish occurs when material structure, tooling, cooling, and machining parameters are not optimally matched. In addition, deviations from standards and permissible material defects such as porosities often present an underestimated risk if no further requirements have been defined with the supplier. Failure to do so risks unnecessary rework, scrap, and increased costs throughout the manufacturing process.

The following solutions can reduce typical errors:

• Process monitoring and cutting data adjustment: Continuous monitoring can be used, for example, to adjust the cutting speed to the given conditions.
• Use homogeneous material (here, e.g., also check for foreign bodies such as LABS)
• Use materials that are suitable for both machining and subsequent processes, or avoid additives such as sulfur that result in poorer weldability.
• Reduce stresses in the workpiece, e.g., by suitable annealing.