Plastic Post and Hub Press Fit Equations / Calculator

Plastics Design Resources

Plastic Press fitting provides a simple, fast and economical means for parts assembly. Press fits can be used with similar or dissimilar materials and can eliminate screws, metal inserts, adhesives, etc. Since plastic materials will creep or stress relieve under continued loading, loosening of the press fit, at least to some extent can be expected. Testing under expected temperature cycles is obviously required.

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Geometry Factor:

Where:

E_p = Modulus of elasticity of considered plastic hub or boss: psi, (N/mm²)

v_p = Poissons Ratio of Hub when different from shaft

σ_a = Allowable design stress for plastic: psi, (N/mm²)

σ_s = Allowable design stress for plastic: psi, (N/mm²)

σ_m = Allowable design stress for plastic: psi, (N/mm²)

σ = Hoop stress: psi, (N/mm²)

i = d_s - d_i = Diametral interference: in, (mm)

i_a = Allowable interference: in, (mm)

Γ = Geometry factor

Case #1

Shaft and Hub have identicle or very simular materials. Hoop stress given i is:

and the allowable interference is:

Case #2

Shaft is metal and hub is plastic, Hoop stress is given i is:

and the interference is:

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