# How to calculate the weight of a gear?

## Main Question or Discussion Point

I don't know if I have to include the weight of a gear in order to proceed on computing the forces acting on the plane of line shaft. If I have to determine it, how do I calculate the weight of the gear (spur gear)?

Related Mechanical Engineering News on Phys.org
anorlunda
Staff Emeritus
I don't know if I have to include the weight of a gear in order to proceed on computing the forces acting on the plane of line shaft.
That depends on how accurate you need to be. We can't answer that question without a lot more specific detail.

If I have to determine it, how do I calculate the weight of the gear (spur gear)?
How would you determine the weight of any object of any shape?

CWatters
Homework Helper
Gold Member
Perhaps approximate the gear to a cylinder. Calculate the volume, look up the density of the material it's made from. Bash the numbers into the calculator.

• Ballena Joseph
If the gear is available, you can simply weigh it on a scale.

If you only have a drawing, you can treat it as a body of revolution (neglecting the teeth) with an outside radius about equal to the pitch radius. This will result in a calculated value that is quite close.

• Ballena Joseph
Perhaps approximate the gear to a cylinder. Calculate the volume, look up the density of the material it's made from. Bash the numbers into the calculator.
I already looked up for the density of material for gear. But how can I calculate the volume? What is the formula?

CWatters
Homework Helper
Gold Member

Much depends upon how closely you want to approximate the volume and hence the mass. If a simple cylinder approximation is sufficient for your purposes, then that will be easy based on what you find on Google.

If the cross section is complicated, you may need to do a volume integration. If you can't do that in closed form, it is always possible to do a numerical integration. This will put to use what you learned in Integral Calculus.

• Ballena Joseph
Much depends upon how closely you want to approximate the volume and hence the mass. If a simple cylinder approximation is sufficient for your purposes, then that will be easy based on what you find on Google.

If the cross section is complicated, you may need to do a volume integration. If you can't do that in closed form, it is always possible to do a numerical integration. This will put to use what you learned in Integral Calculus.
I found a formula for the volume of gear, that is (πD/4)*b(face width) which is similar to the formula for volume of cylinder.

I found a formula for the volume of gear, that is (πD/4)*b(face width) which is similar to the formula for volume of cylinder.
That expression is exact, with two provisions:
1) provided the gear body is a flat disk (no raised hub or rim);
2) provided you know what diameter to use.
Somewhere near the pitch diameter is the correct value for the diameter, but that is not exactly correct. I know of no way to specify exactly what the correct diameter is.

• Ballena Joseph
The formula you quoted will not do well at all for a gear of the sort shown in the attached figure. #### Attachments

• 36.1 KB Views: 2,110
The formula you quoted will not do well at all for a gear of the sort shown in the attached figure.View attachment 221557
I have no choice but to assume that the gear is flat and there is no hub or rim.