Two important concepts in gearing are pitch surface area and pitch position. 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 an ordinary gear is the shape of a cylinder. The pitch angle of a gear is the angle between your encounter of the pitch surface and the axis.
The most familiar kinds of bevel gears have pitch Screw Air Compressor angles of less than 90 degrees and they are cone-shaped. This kind of bevel gear is called external because the gear teeth stage outward. The pitch areas of meshed external bevel gears are coaxial with the apparatus shafts; the apexes of the two areas 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 so are called internal bevel gears.
Bevel gears which have pitch angles of exactly 90 degrees possess teeth that time outward 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 equal amounts of teeth and with axes at right angles.
Skew bevel gears are those for which the corresponding crown equipment has the teeth that are straight and oblique.