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Mechanical engineering other topics FAQ

Internet Resources

Press Fits - quick calculator by GregLocock
Posted: 8 Apr 06 (Edited 16 May 07)

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

   where 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:-


where 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.

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