Moment of Inertia of screw drive.

[konform]

Can anyone help me calculate the polar moment of inertia of a screw based transmission shaft? I'm trying to calculate the size of the screw I will need to transmit a certain amount of power. Thanks

 

[codeeng]

Polar moment of inertia for a shaft is equal to twice the moment of inertia, or 0.098 D^4.

 

[konform]

But because it is a screw, the diameter is different depending on where I take the cross section. Doesn't that make a difference? Which diameter do I take?

 

[codeeng]

The smallest one.

 

[Allen]

Isn't the following link what you are looking for?

http://www.engineersedge.com/motors/lead_screw_drive_system.htm

 

[konform]

Yes, that is very useful, thank you.