2. a) A gear in your drill will be made of Zytel 101 nylon 66. The torque it wil

2. a) A gear in your drill will be made of Zytel 101 nylon 66. The torque it will encounter in normal
operation is 20 inch-pounds. If this gear has a pitch diameter (equivalent to a hub outside diameter)
of 1.25 inches and is mounted to a 0.25″ diameter steel shaft, with a contact axial length(thickness) of
0.125 inches, what is the Push-on force, the Contact pressure and what is the necessary reduction in
gear internal diameter, Interference amount, to avoid slippage.
Givens:
Steel tensile modulus, 30,000,000 psi
Steel Poisson ratio, 0.29
Coefficient of friction, 0.40
Nylon tensile modulus, 450,000 psi
Nylon Poisson ratio, 0.41
b) The life expectancy is 5 years, given the chart below, how much of a safety factor would you build
in for stress relaxation in a 50% relative humidity environment, and what should your revised
interference amount be

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