drukhoek

Drukhoek, in gear theory also called the pressure angle, is a fundamental parameter in involute gear pairs. It is defined as the angle between the line of action— the path along which contact forces act between meshing teeth— and the common tangent to the gear pitch circles at the point of contact. The drukhoek determines how forces are transmitted between gears and influences tooth strength, load distribution, and the kinematics of meshing.

In standard gear profiles the drukhoek is specified as a fixed value, commonly 14.5°, 20°, or 25°. The most widely used value in modern metric gears is 20°. The choice of pressure angle affects the geometry of the tooth flank, the width of contact, and the efficiency of force transmission. A larger drukhoek generally increases the radial component of the transmitted force, which can raise bearing loads and wear, while reducing the length of the contact path and the contact ratio. Conversely, a smaller drukhoek can improve contact ratio but may require different manufacturing tolerances and affect tooth strength.

Relation to design: The base circle radius rb of a gear is related to the pitch radius r by rb = r cos(phi), where phi is the drukhoek. This relationship links pressure angle to tooth geometry and determines bending strength, contact stresses, and manufacturing feasibility.

See also: Gear theory, Involute gearing, Contact ratio, Base circle.