How this calculation works
An interference-fit hub may need temporary bore clearance to pass over a shaft during assembly. This page asks a geometric thermal-expansion question: how much uniform hub temperature rise would create an entered diametral clearance while the shaft stays unheated?
Required hub ΔT = [(shaft diameter + clearance)/cold bore − 1]/αA worked example
A 50.05 mm shaft and 50 mm cold bore have 0.05 mm interference. Adding another 0.05 mm temporary clearance requires a 50.10 mm bore. At coefficient 12 microstrain per degree, the ideal hub rise is 166.667 °C, reaching 186.667 °C from twenty.
Good to know
Uniform linear expansion only, with an unchanged shaft temperature. The calculation excludes thermal gradients, handling time, material temperature limits, contact pressure and retention torque. It is not a heating procedure or a fit-class recommendation.
Reference: MIT — mechanics of materials (opens in a new tab) ↗
What this model answers
An interference-fit hub may need temporary bore clearance to pass over a shaft during assembly.
This page asks a geometric thermal-expansion question: how much uniform hub temperature rise would create an entered diametral clearance while the shaft stays unheated?
The Linear thermal expansion calculator calculates free dimensional expansion; this page inverts the same linear relationship for the bore clearance required during a hub-only heating scenario.
Keep the input conventions consistent
All dimensional entries are diameters or diametral differences, not radii.
The expansion coefficient is entered in millionths per degree Celsius. Initial temperature is common to both parts before the hub-only heating scenario begins.
Read the result carefully
The required bore increase includes both cold interference and desired temporary clearance.
Those are different quantities. A temperature that merely removes the interference leaves zero modeled clearance and may be inadequate for a real assembly operation.
The required expansion belongs to the relevant bore diameter and stated interference convention. Confusing radial interference with diametral interference changes the target expansion. The modeled assembly-temperature difference addresses geometric clearance only; it does not determine the final contact pressure, retention torque or acceptable material heating limit.
Work through the numbers
A 50.05 mm shaft and 50 mm cold bore have 0.05 mm interference.
Adding another 0.05 mm temporary clearance requires a 50.10 mm bore. At coefficient 12 microstrain per degree, the ideal hub rise is 166.667 °C, reaching 186.667 °C from twenty.
Where the calculation stops
Uniform linear expansion only, with an unchanged shaft temperature.
The calculation excludes thermal gradients, handling time, material temperature limits, contact pressure and retention torque. It is not a heating procedure or a fit-class recommendation.
A few questions, answered
Does this calculate the final contact pressure?
No. Contact pressure requires elastic properties and the coupled deformation of both parts after cooling.
What should I change in the comparison?
Remove the extra assembly clearance and isolate the expansion needed only to cancel interference.