Angles of threading taps

A geometrically defined cutting wedge essentially consists of three fundamental angles that together form a right angle in the plane of the cutting: The clearance angle, the wedge angle, and the rake angle. Where are these angles located on the tap, and how do the three angles affect thread cutting?

Clearance angle (α):

This angle lies between the flank (relief) face of the cutting edge and the machined surface of the workpiece. Its primary function is to prevent friction between these two surfaces, or at least to reduce it to a minimum. An appropriate clearance (or relief) angle ensures that the flank face clears the workpiece freely, thereby preventing excessive wear and unnecessary heating.

Clearance angle too small: Results in high friction forces and premature wear of the tap.

Clearance angle too large: can make the cutting edge unstable under load and may cause the cutting edges to chip or break off.

For hard to machine materials (e.g. stainless steels), taps with a larger clearance angle should be used to compensate for higher cutting forces. When tapping soft or viscous materials (e.g. aluminium or copper), a smaller clearance angle should be used to ensure greater cutting stability. As a general rule, the clearance angle should be as small as possible but as large as necessary.

Wedge angle (β):

The wedge angle is formed between the rake face and the flank face of the tap. It forms the actual tool wedge and therefore carries the cutting edge. Its magnitude directly determines the stability and mechanical load-bearing capacity of the cutting element.

Large wedge angle: More stable cutting edge, higher cutting forces, for hard materials.

Small wedge angle: Sharper cutting edge, penetrates more easily, requires less force, but is less stable.

Rake angle (γ):

This angle is located between the rake face of the tap and a line perpendicular to the workpiece surface. The rake angle has the greatest influence on chip formation and chip evacuation away from the tap. It determines the cutting performance of the tap and must be adapted to the mechanical properties of the material being machined.

Summary

The three angles are in a fundamental geometric relationship such that their sum always equals 90°. This equation, α + β + γ = 90° is the key to understanding the mutual interdependence of cutting edge geometry. Any change in one angle inevitably leads to an adjustment of the other angles. The geometry therefore cannot be regarded as the sum of individual, independent angles, but rather as a closed system of compromises. In VÖLKEL taps, these three angles are optimally matched to the intended applications and the materials to be machined.

⚠️️ The wedge angle (β) is the key variable between sharpness and stability. The description of the wedge angle is inherently linked to its function as the carrier of the cutting edge. It represents the physical element that absorbs the mechanical stresses of the cutting process (in this case, thread cutting).