Two important concepts in gearing are pitch surface area and pitch angle. The pitch surface area of a gear is the imaginary toothless surface area that you would possess by averaging out the peaks and valleys of the average person teeth. The pitch surface area of a typical gear is the form of a cylinder. The pitch angle of a equipment is the angle between the face of the pitch surface area and the axis.
The most familiar types of bevel gears have pitch angles of significantly less than 90 degrees and therefore are cone-shaped. This type of bevel gear is called external since the gear teeth stage outward. The pitch areas of meshed exterior bevel gears are coaxial with the gear shafts; the apexes of the two surfaces are at the idea of intersection of the shaft axes.
Bevel gears which have pitch angles in excess of ninety degrees possess teeth that time inward and are called internal bevel gears.
Bevel gears that have pitch angles of precisely 90 degrees possess teeth that point outward planetary gearbox parallel with the axis and resemble the points on a crown. That is why this kind of bevel gear is named a crown gear.
Mitre gears are mating bevel gears with the same amounts of teeth and with axes at right angles.
Skew bevel gears are those for which the corresponding crown gear has the teeth that are straight and oblique.