Two important principles in gearing are pitch surface and pitch angle. The pitch surface of a gear may be the imaginary toothless surface area that you would have got by averaging out the peaks and valleys of the individual teeth. The pitch surface of a typical gear is the form of a cylinder. The pitch angle of a equipment is the angle between the encounter of the pitch surface area and the axis.

The most familiar kinds of bevel gears have pitch angles of significantly less than 90 beval gearbox degrees and they are cone-shaped. This type of bevel gear is named external because the gear teeth point outward. The pitch surfaces of meshed external bevel gears are coaxial with the apparatus shafts; the apexes of both areas are at the idea of intersection of the shaft axes.

Bevel gears which have pitch angles in excess of ninety degrees have teeth that point inward and are called internal bevel gears.

Bevel gears that have pitch angles of precisely 90 degrees possess teeth that time outward parallel with the axis and resemble the points on a crown. That is why this type of bevel gear is called a crown gear.

Mitre gears are mating bevel gears with equivalent numbers of teeth and with axes at right angles.

Skew bevel gears are those that the corresponding crown equipment has teeth that are directly and oblique.