Understanding thread cutting

From hand taps to CNC processes.

Thread cutting is one of the oldest and most precise metalworking processes. Whether in mechanical engineering, the automotive industry, or precision mechanics, nothing works without a thread. Nevertheless, the amount of know-how and experience that goes into a clean threaded connection is often underestimated.

What does thread cutting actually mean?

Thread cutting involves cutting a spiral groove – the so-called thread – into a pre-drilled hole (internal thread) or onto a cylinder (external thread). This creates a force-locking and form-fitting connection that remains detachable – ideal for all types of screw connections.

The basic principle is simple: material is removed by cutting, with the geometry of the thread precisely following that of the tool. Precision is crucial – even the smallest deviations in pitch or diameter can render the thread unusable.

From hand tap to CNC machine

In the past, threads were cut by hand – using a set of pre-tapping tools, intermediate cutters, and finishing cutters. This method is still used in workshops today, for example, for repairs or individual parts.

CNC-controlled processes now dominate industrial manufacturing. Taps, thread mills, and thread formers (also called thread forming tools) are used here, which operate precisely and repeatably. The advantages are obvious:

  • Higher process reliability

  • Shorter processing times

  • Longer service life thanks to optimized materials and coatings

Procedure at a glance

1. Thread cutting (machining)

The classic method: A tap removes the material by machining. This creates chips that must be removed. This is ideal for many materials, but is prone to problems with tough materials or small holes.

2. Thread forming (chipless)

Here, the material is displaced instead of cut. This ensures greater strength , better surface quality, and no chip formation – ideal for ductile materials such as aluminum or structural steel.

3. Thread milling

The thread is milled spirally. This method allows for flexible pitches and diameters with a single tool—particularly interesting for CNC machining.

Material and tool selection

Not every tool is suitable for every material. Stainless steel requires different cutting geometries and coatings than aluminum.
A few basic rules:

  • Aluminum: sharp cutting edges, uncoated or TiN-coated tools

  • Stainless steel: high toughness, better TiCN or TiAlN coating

  • Cast iron: brittle, rather robust geometries with large chip space

Cooling is also crucial: Too little lubrication leads to friction, heat, and tool breakage; too much can cause chips to stick together. Finding the right balance is a matter of experience.

Ensuring quality: Control is mandatory

After thread cutting, measurements are taken. Whether using a thread ring gauge, micrometer, or digital inspection system – checking the pitch, flank angle, and core diameter is a prerequisite for a reliable connection.
Test reports are now standard, especially in safety-relevant applications (e.g. vehicle construction or mechanical engineering).

Future: Digital Precision

Digitalization is also transforming thread cutting. "Smart tools" with integrated sensors monitor torque, cutting speed, and temperature in real time. This allows sources of error to be identified early – and further increases process reliability.

The combination of experience and digitalization is becoming the new standard in modern manufacturing.

💡 Practical tip: When cutting threads, the preparatory work determines the result .
A precisely fitting core hole diameter, cleanly deburred edges and sufficient cooling lubricant not only prevent tool breakage – they also significantly extend the service life.

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