Two important principles in gearing are pitch surface and pitch angle. The pitch surface area of a gear is the imaginary toothless surface area that you would have by averaging out the peaks and valleys of the average person 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 and the axis.
The most familiar types of bevel gears have pitch angles of 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 surfaces of meshed external bevel gears are coaxial with the gear shafts; the apexes of both areas are at the point of intersection of the shaft axes.
Bevel gears that have pitch angles in excess of ninety degrees have teeth that point inward and so are called internal bevel gears.
Bevel gears that have pitch angles of specifically 90 degrees possess teeth that time beval gear china outward parallel with the axis and resemble the factors on a crown. That is why this kind of bevel gear is named a crown gear.
Mitre gears are mating bevel gears with equivalent numbers of teeth and with axes in right angles.
Skew bevel gears are those that the corresponding crown gear has the teeth that are directly and oblique.