Bevel gear and types

Bevel gears are gears in which the axes of two shafts intersect and the tooth surfaces of the gear itself are conical.Bevel gears are usually mounted on shafts 90 degrees apart, but can be designed to work at other angles as well.The pitch surface of a bevel gear is a cone, called a pitch cone. Bevel gears transfer energy from linear to vertical power, making them useful in machines that are widely used in mechanical settings.

Introduction 

Two important concepts in transmissions are pitch surface and pitch angle.The pitch face of a gear is an imaginary toothless surface that you can obtain by averaging the peaks and valleys of the individual teeth.The pitch surface of ordinary gears is cylindrical.The pitch angle of a gear is the angle between the face of the pitch face and the axis.The most common bevel gears have a pitch angle of less than 90 degrees and are therefore tapered.This type of bevel gear is called an external bevel gear because the teeth point outward.The pitch surfaces of the meshing external bevel gears are coaxial with the gear shaft; the apexes of the two surfaces are at the intersection of the shaft axes.The use of original bevel gears is more important to the reliability of the axle than any other spare part.The teeth of the bevel gear with a pitch angle greater than 90 degrees face inward, which is called an internal bevel gear.A bevel gear with a pitch angle of exactly 90 degrees has the teeth pointing outward parallel to the axis, resembling a point on a crown, hence the name crown gear.

Types

Mitre gears

A miter gear is a special case of a bevel gear with the same number of teeth.The shafts are at right angles to each other and the gears have matching pitch faces and angles, with conical pitch faces.Mitered gears can be used to transmit rotational motion through a 90 degree angle in a 1:1 ratio.

Bevel gear geometry

A cylindrical gear tooth profile corresponds to an involute (i.e. a triangular wave projected on the circumference of a circle), while a bevel gear tooth profile is octahedral [needs definition] (i.e. a triangular wave projected on a sphere normal to the circle).All conventional bevel gear generators (e.g. Gleason, Klingelnberg, Heidenreich & Harbeck, WMW Modul) manufacture bevel gears with eight-sided tooth profiles. Important note:For 5-axis milling of bevel gear sets, it is important to choose the same calculation/layout as for traditional manufacturing methods.Simplified calculations based on equivalent cylindrical gears in normal section with involute tooth profiles for bevel gears show deviated tooth profiles with a reduction in tooth strength of 10-28% without offset and 45% with offset [Diss. Hünecke, TU Dresden]. Also, those "involute bevel gear sets" make more noise.

List of drawing symbols

Teeth

There are two issues regarding tooth shape. One is the cross-sectional profile of the individual tooth.The other is the line or curve on which the tooth is set on the face of the gear: in other words the line or curve along which the cross-sectional profile is projected to form the actual three-dimensional shape of the tooth.The primary effect of both the cross-sectional profile and the tooth line or curve is on the smoothness of operation of the gears. Some result in a smoother gear action than others.

Tooth line

The teeth on bevel gears can be straight, spiral or "zerol".

Straight tooth lines

In straight bevel gears, the teeth are straight and parallel to the generators of the cone.This is the simplest form of bevel gear.It resembles a spur gear, only conical rather than cylindrical.The gears in the floodgate picture are straight bevel gears.In straight bevel gear sets, when each tooth engages, it impacts the corresponding tooth and simply curving the gear teeth can solve the problem.

Spiral tooth lines

Spiral bevel gears have their teeth formed along spiral lines.They are somewhat analogous to cylindrical type

Helical gears

 in that the teeth are angled; however, with spiral gears, the teeth are also curved.The advantage of the spiral tooth over the straight tooth is that they engage more gradually.The contact between the teeth starts at one end of the gear and then spreads across the whole tooth.This results in a less abrupt transfer of force when a new pair of teeth come into play.With straight bevel gears, the abrupt tooth engagement causes noise, especially at high speeds, and impact stress on the teeth which makes them unable to take heavy loads at high speeds without breaking.For these reasons, straight bevel gears are generally limited to use at linear speeds less than 1000 feet/min; or, for small gears, under 1000 rpm.

Zerol tooth lines

Zerol bevel gears are an intermediate type between straight and spiral bevel gears.Their teeth are curved, but not angled.Zerol bevel gears are designed with the intent of duplicating the characteristics of a straight bevel gear, but they are produced using a spiral bevel cutting process.