By @GregLocock and @Desertfox

**The equations are called Lame’s equations.**

Here’s an online calculator:

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.]*