# Need help calculating Shear on a 5/8 square key

• vwmeche94
In summary, to calculate the shear on a 5/8" square key, first determine the torque applied to the shaft and then use it to calculate the shear stress on the key. It is recommended to limit the shear stress to 40% of the yield stress for design purposes.

#### vwmeche94

Need help calculating Shear on a 5/8" square key

PF,

I am trying to figure out how to calculate the shear on a 5/8" x 5/8" x 3-1/2"L standard shaft key, when the OD of the shaft it fits into is 3". A tire of ~40" dia rides on the shaft and at any given time, let's say a load of 20,000lbs is applied to put a bending moment on the shaft at the surface of the tire. If I assume the shaft is fixed for brief moment in time,
what is the maximum shear I can apply to the key before it gives (breaks)?

A simple approach is as follows:

For the shaft to be "fixed for a brief moment" the net torque must equal zero:

So torque = F X Distance = F_tire X radius_tire = F_shaft X radius_shaft

Solve for F_shaft.

Now F_shaft will be applied in shear to your shaft key. The area in shear is : A_shear = 5/8" X 3.5 ".

And the shear stress is now:

shear_stress = F_shaft / A_shear.

When shear_stress is greater then the tensile shear stress of the shaft key, it will break (in principle).

For design, it is better to limit the calculated shear stress to about 40% of the yield stress.

## What is shear?

Shear is a type of stress that occurs when two forces act parallel to each other in opposite directions, causing layers of an object to slide past each other.

## What is a 5/8 square key?

A 5/8 square key is a mechanical fastener used to connect rotating machine components, such as gears, pulleys, and shafts. It has a square cross-section with a width of 5/8 inches.

## How do I calculate shear on a 5/8 square key?

To calculate shear on a 5/8 square key, you will need to know the shear strength of the material the key is made of and the applied force acting on the key. Then, you can use the equation: Shear = Force / Area. In this case, the area would be the cross-sectional area of the key.

## Why is it important to calculate shear on a 5/8 square key?

Calculating shear on a 5/8 square key is important to ensure the key is strong enough to withstand the forces acting on it. If the shear stress exceeds the shear strength of the key, it could lead to failure and damage to the machine.

## What are the units of shear stress?

The units of shear stress are typically expressed in pounds per square inch (psi) or newtons per square meter (Pa). Other common units include kilopascals (kPa) and megapascals (MPa).