Question

The following are the data for two crossed helical gears used for speed reduction:
Gear I : Pitch circle diameter in the plane of rotation 80 mm and helix angle ${30}^o$
Gear II : Pitch circle diameter in the plane of rotation 120 mm and helix angle ${22.5}^o$
If the input speed is 1440 rpm, the output speed in rpm is

• A. 1200
• B. 900
• C. 875
• D. 720

Answer 1

The correct option is B 900

For helical gear:

Velocity ratio $=\frac{N_2}{N_1}=\frac{D_{1}cos\varphi }{D_{2}cos\varphi }$

$=\frac{80cos{30}^o}{120cos{22.5}^o}$

$\therefore$ $N_2=1440\times 0.625$

$=900\text{rpm}$