# Percentage saving in weight of sloid shaft Vs hollow shaft

I have calculated the external diameter and the solid shaft is to be replaced by a hollow shaft whose internal diameter equals 60% of the external diameter, the length, material, and maximum shear stress remaining unchanged.

How can I calculate the percentage saving in weight?
What are the equations that are relative to this?

Thank u for ur help

#### tiny-tim

Homework Helper
Welcome to PF!

I have calculated the external diameter and the solid shaft is to be replaced by a hollow shaft whose internal diameter equals 60% of the external diameter, the length, material, and maximum shear stress remaining unchanged.

How can I calculate the percentage saving in weight?
What are the equations that are relative to this?

Thank u for ur help

Hint: volume = cross-section-area times height …

so how much is the cross-section-area reduced?

#### nvn

Homework Helper
adam333: For the hollow versus solid shaft, hold applied torque and maximum shear stress constant, and set inside diameter of the hollow shaft equal to 60 % of the outside diameter of the hollow shaft. List relevant equations, and show your work.

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