Two important concepts in gearing are pitch surface and pitch angle. The pitch surface area of a gear is the imaginary toothless surface that you would possess by averaging out the peaks and valleys of the individual 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 kinds 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 external bevel gears are coaxial with the apparatus 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 which have pitch angles of exactly 90 degrees have teeth that time 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 at right angles.