Gear drives

5
Bevel Gears

o The bevel gears are used for transmitting power at a constant velocity ratio
between two shafts whose axes intersect at a certain angle (Khurmi, Gupta,
2005).
o Bevel gears are used to connect intersecting shafts, usually but not at 90
degrees (Faires, 1965).

The bevel gears may be classified into the following types, depending upon the angles
between the shafts and the pitch surfaces.
1. Miter gears - when equal bevel gears connect two shafts whose axes intersect
at right angle, they are known as miter gears.
2. Angular bevel gears - when the bevel gears connect two shafts whose axes
intersect at an angle other than a right angle, then they are known as angular
bevel gears.
3. Crown bevel gears - when the bevel gears connect two shafts whose axes
intersect at an angle greater than a right angle and one of the bevel gears has a
pitch angle of 90º, then it is known as a crown gear.

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Pitch Angle for Bevel Gears

Figure 4-1

PROBLEM
Compute the pitch angle of a bevel gear given the pinion’s number of teeth of 14 and 42 teeth on
the gear.

SOLUTION

Tp = 14
Tg = 42

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Formula

Pitch angle = tan-1

Pitch angle = tan-1 = 18.40

PROBLEM
Find the ratio of a pair of bevel gears with a 15-tooth pinion and a 60-tooth gear.

SOLUTION
Tp = 14
Tg = 42

Formula
GR =

GR =

GR =

PROBLEM
Calculate the velocity of a gear with a pitch diameter of 4.5" turning at 800 RPM.

SOLUTION

Dp = 4.5"
N = 800 rpm
Formula

V =.262D x rpm

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V =.262 (4.5) x 800

V =943 fpm

PROBLEM
Determine the circular pitch (Pc) of a 48-tooth gear with an 8-inch pitch diameter.

SOLUTION
Pc = π (8) ÷ 48

Pc = 0.5236 inches

Design Exercises

PROBLEM
A cast iron bevel gear has a pitch diameter of 600mm and a pitch angle of 30degree. The module
is 2.5. Determine the permissible endurance load. The teeth are 20-degree full depth.

SOLUTION

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PROBLEM
Two cast iron bevel gears having pitch diameters of 80 mm and 100mm respectively and to
transmit 11/4 Kw at 1100RPM of the pinion. The tooth profile is of 20 degree full depth. Take
(s0=55MN/m2).
(a) determine the face width and the required module from stand point of strength
(b) Check the design from stand point of dynamic load and wear C=110 kN/m.

SOLUTION

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PROBLEM
A 100 kW, 750-RPM motor is required to drive a centrifugal pump continuously at 250 RPM by
means of straight bevel gears connected at 90m-degree shaft angle. The starting torque is 20%
greater that rated torque (a) Design the gears. (b) Could the same pinion is use to drive another
pump at 150RPM? Give brief explanation.

SOLUTION

PROBLEM
Two steel bevel gears connects shaft at right angle. The pinion has a BHN of 300 and the gear
has hardness 200. The teeth are 14.5 full depths and the module is 3. The number of teeth on
pinion has 64. The face width is 40mm. determine the wear load.

SOLUTION

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PROBLEM
A pair of 4 pitch 20 degree involutes machine cut bevel gear has a 2:1 reduction. The pitch
diameter of the driver is 250mm and runs at 200RPM. Selecting the suitable material for the
pinion and the gear determine the various parameter of gear set.

SOLUTION

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PROBLEM
A pair of bevel gear is mounted on shafts that are at 90 degree apart. The set is to transmit 90 Kw
at 300RPM. The pinion has 150mm outside pitch diameter; 50 mm face width, a diametral pitch
of 6, and 20 degree full depth. For a velocity ratio 0.4, determine the forces acting on gear tooth.

SOLUTION

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Assignment # __
Find machinery or device/machines that have bevel gear application. Have a picture of it and
identify the details of the gear (i.e. tooth thickness, face width, pitch diameter, etc.) and compute
the power needed to operate such machine. Submit this requirement(s) on ___________.
Notes

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DESIGN PROBLEM # 5

Name: Rating:
Course/Yr: Date:

BEVEL GEAR

PROBLEM
Design the full-depth 14.50 teeth of a pair of straight bevel gears to transmit 30 hp at 1200 rpm of
the pinion. The velocity ration should be about 3 and the pinion should have 18 teeth. Determine
the following: Pd, face width, Dp, and pitch cone angles for the gears.

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DESIGN PROBLEM # 5 bevel gear continuation

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