Two important principles in gearing are pitch surface and pitch position. The pitch surface of a gear is the imaginary toothless surface area that you would have got by averaging out the peaks and valleys of the average person teeth. The pitch surface of an ordinary gear is the shape of a cylinder. The pitch angle of a gear is the angle between the encounter of the pitch surface and the axis.
The most familiar kinds of bevel gears have pitch angles of less than 90 degrees and they are cone-shaped. This kind of bevel gear is called external because the gear teeth point outward. The pitch areas 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 of beval gear china greater than ninety degrees have teeth that point inward and are called internal bevel gears.
Bevel gears that 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 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 that the corresponding crown gear has tooth that are straight and oblique.