# Press Fits - quick calculator

The equations are called Lame’s equations.

Here’s an online calculator:

http://www.tribology-abc.com

Under interference fits. You have to log in to be able to change the pin diameter.

Alternatively desertfox looked up the equations, so you can roll your own:

Here are the formulas you need:

``````       Pa= f*3.142*d*L*Pc
``````
• f=friction coefficient
• Pc=contact pressure between the two members
• d= nominal shaft dia
• L=length of external member.
• Pa= axial force required to interference fit

To calculate Pc for a given interference use the formula:

Pc=x/[Dc*[((Dc^2+Di^2)/(Ei(Dc^2-Di^2))+((Do^2+Dc^2)/(Eo*(Do^2-Dc^2))-((Ui/Ei)+Ui/Eo))]

• x = total interference
• Dc=dia of shaft
• Di = inner dia of shaft(this is zero for solid shaft)
• Do= outside dia of collar
• Uo=poissons ratio for outer member
• Ui=poissons ratio for inner member
• Eo=modulus of elasticity for outer member
• Ei=modulus of elasticity for inner member

[This formula for Pc will simplify if the materials are the same.]