Inputs
Results
Interference pressure p ≈ E × δ / (2 × r² × outer). Press force = p × μ × π × d × L.
What this calculator actually solves
Press-fit and shrink-fit joints depend on the interference — the difference between shaft and bore diameters. As interference increases, the joint becomes stronger but harder to assemble. This calculator estimates the press force required for a given interference, and the equivalent temperature change if you'd rather use a shrink fit (heating the hub or cooling the shaft).
Who this is for
Machinists and fab techs assembling bearings, gears, and pulley hubs where a press fit is the spec.
Builders restoring old equipment with shrink-fit assemblies that need re-fitting.
How to read the results
If the press force exceeds your press capacity, switch to shrink-fit (heating the hub or cooling the shaft with dry ice or LN2).
For shrink fit: heating to 200°C typically gives ~0.1% expansion, which is enough for moderate interference on small parts.
Limitations
Real press-fit force is sensitive to surface finish. We use a typical friction coefficient; lapped surfaces have lower friction, and rough surfaces much higher.
This calculator assumes a solid shaft. Hollow shafts reduce the press force significantly.
Frequently Asked Questions
Press fit or shrink fit?
For interference under 0.001" (25 µm), a hydraulic or arbor press is fine. Above 0.001", shrink fit is faster and avoids scoring the bore. Above 0.003", shrink fit is almost mandatory.
How much do I heat the hub?
Steel expands ~12 µm/m/°C. To get 50 µm of clearance on a 30 mm bore, you need ΔT ≈ 50 / (30 × 12) ≈ 140°C. Most ovens top out at 200°C, which is well within safe limits for hardened steel hubs.
My press fit keeps galling. What's wrong?
Either the surface finish is too rough, the alignment is off, or the press speed is too slow. Slow pressing generates more heat at the interface. Use anti-seize on the shaft and press at a steady 5–10 mm/sec.
About this tool
What this tool is for: Press Fit Force Calculator is a workbench reference for working mechanics, machinists, restoration shops, and serious hobbyists. It is built because the usual online calculators skip the friction loss, the sign convention, the unit conversion, or the engineering code that actually matters on the job.
Purpose and scope
Assembly force and shrink-fit allowance for shaft-in-hub press fits. Assumes a uniform interference and no lubrication — change the friction factor if you are using a lubricant.
How to use the body of this page
The sections above this footer — “What this calculator solves,” “Who this is for,” “How to read the results,” and “Limitations” — describe in detail what the formula does, why a tech would use it, how to interpret the number, and where the model is wrong. The FAQ block answers the three or four questions most asked about this specific tool. Together they make up the “About” content for this page; you do not need to look elsewhere.
Known limitations of every MechCalc Pro tool
All calculators on MechCalc Pro run the math in your browser and assume standard conditions (sea-level pressure, ambient temperature, dry friction, textbook geometry). They do not capture manufacturing tolerances, the wear state of your specific parts, environmental extremes, regulatory codes (ASME, DOT, AWS D1.1, etc.), or the load spectrum of your job. They are not a substitute for a stamped engineering review on safety-critical work.
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Disclaimer
All content on this page, including formulas and calculator outputs, is provided for general informational and educational purposes only. It is not professional engineering advice, it is not a substitute for manufacturer specifications, and it is not a warranty of fitness for any particular purpose.
Mechanical, hydraulic, and welding work can cause serious injury, death, or property damage if performed incorrectly. Numbers produced by this calculator reflect simplified textbook models; they do not capture manufacturing tolerances, material defects, environmental conditions, wear, fatigue, regulatory codes (such as ASME, DOT, or AWS), or the specific service conditions of your job. Always cross-check critical values against the original equipment manufacturer's published specifications and a qualified engineer's review before committing to the job.
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