Two important ideas in gearing are pitch surface and pitch position. The pitch surface of a gear is the imaginary toothless surface that you would have by averaging out the peaks and valleys of the average person teeth. The pitch surface area of a typical gear is the shape of a cylinder. The pitch angle of a equipment is the angle between your encounter of the pitch surface and the axis.
The most familiar types of bevel gears have pitch angles of significantly less than 90 degrees and they are cone-shaped. This type of bevel gear is called external because the gear teeth point outward. The pitch surfaces of meshed exterior bevel gears are coaxial with the gear shafts; the apexes of the two surfaces are at the point of intersection of the shaft axes.
Bevel gears which have pitch angles of greater than ninety degrees possess teeth that time inward and are called internal bevel gears.
Bevel gears that have pitch angles of exactly 90 degrees have teeth that point outward parallel with the axis and resemble the factors on a crown. That’s why this type of bevel gear is called a crown gear.
Mitre gears are mating bevel gears with the same amounts of teeth and with axes in right angles.