An interference (press
& shrink) fit is a frictional shaft-hub connection. Joint pressure in
the friction surface is necessary for the torque (force) transmission and this
pressure is generated by the deformation of shaft and hub. Suitable assembly
method shall be selected between shrink fit and press fit. In the
press fit case, assembly operation is done with large amount of forces and
forcing shaft into the hub. In the
shrink fit case, assembly operation is done by relative size change of parts
with the help of heat treatment. Typical examples of press fit is fitting shafts
into the bearing and bearings into the housings.

For
the preferred interference tolerances for shaft & hub connection in metric and inch fits, visit
"Supplements" section.

The Interference (press & shrink) fit calculator is developed to calculate
interference parameters such as assembly (press) force, required temperature for
shrink fit, Von Mises stresses occurred on shaft and hub, factor of safety
values.

Design factor (nd): The ratio of failure stress to allowable stress.
The design factor is what the item is required to withstand .The design factor is defined for an application
(generally provided in advance and often set by regulatory code or policy) and is not an actual calculation.

Factor of Safety (Safety Factor):
The ratio of failure stress to actual/expected stress. The difference between the factor of safety (safety factor)
and design factor is: The factor of safety gives the safety margin of designed part against failure. The design factor
gives the requirement value for the design. Safety factor shall be greater than or equal to design factor.

Modulus of elasticity (Young’s
modulus): The rate of change of unit tensile or compressive stress with respect to unit tensile or compressive strain
for the condition of uniaxial stress within the proportional limit. Typical values: Aluminum: 69 GPa, Steel: 200GPa.

Poisson’s ratio: The ratio of lateral unit strain to longitudinal unit
strain under the condition of uniform and uniaxial longitudinal stress within the proportional limit.

Press fit: Assembly of parts with very large amounts of force. Assembly operation
is done with presses.

Proportional Limit:
The largest value of stress up to which a linear relation still exist between stress and strain (Hooke’s Law).

Shear stress: A form of a stress acts parallel to the surface (cross section)
which has a cutting nature.

Shrink fit: Assembly of parts by
relative size change with the help of heat treatment. This is usually achieved
by heating and cooling one component before assembly and allowing it to return
to the ambient temperature after assembly.

Stress: Average force per unit area which results strain of material.

Stress Concentration Factor:
Dimensional changes and discontinuities of a member in a loaded structure causes
variations of stress and high stresses concentrate near these dimensional
changes. This situation of high stresses near dimensional changes and
discontinuities of a member (holes, sharp corners, cracks etc.) is called stress
concentration. The ratio of peak stress near stress riser to average stress over
the member is called stress concentration factor.

Von Mises: A theory used to
estimate the yielding of ductile materials. The Von Mises criteria states that failure occurs when the energy of distortion
reaches the same energy for yield failure in uniaxial tension test.

Yield strength: The stress at which a material
exhibits a specified permanent deformation or set. Example: Al6061-T6: 145 Mpa