Answer to Question 1
Clearance is defined as the distance between the top of the tooth of one gear and the bottom of the meshing tooth space. (See figure 9-10). Backlash is the amount of side clearance of a gear tooth when two teeth mesh. More specifically, it is the space between meshing teeth measured at the pitch circle.
Answer to Question 2
The 20 pressure angle gives the gear tooth a wider base, resulting in greater strength and allows the use of smaller gears with fewer teeth for more compact and economical gear drives.
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