Press Fit Calculator
Calculate interference, contact pressure, press force, torque capacity, and hoop stress for press-fit assemblies such as shafts and hubs. This tool is essential for designing reliable interference fits in mechanical and CNC components.
Press Fit / Interference Fit
Calculator
Quick Answer
- Interference = Shaft OD − Hub ID
- Contact pressure depends on interference & material elasticity
- Press force = Pressure × Contact area × Friction
Core Formulas
Diametral Interference
delta = D_ – D_
Contact Pressure (Simplified Thick Cylinder Model)
p = frac cdot frac
Axial Press Force
F = pi cdot D cdot L cdot p cdot mu
Torque Capacity
T = frac
Hub Hoop Stress
sigma_ approx p cdot frac
How to Use
- Enter Shaft Outer Diameter (OD)
- Enter Hub Bore Inner Diameter (ID)
- Input Hub Outer Diameter (OD)
- Set Fit Length (contact length)
- Enter Material properties:
- Elastic modulus (E)
- Poisson's ratio (ν)
- Enter Friction coefficient (μ)
👉 The calculator will output:
- Interference value
- Contact pressure
- Required press force
- Torque transmission capacity
- Hub stress
Engineering Meaning of Each Output
Interference (mm)
- Positive → interference fit
- Determines tightness
Contact Pressure (MPa)
- Key factor for holding strength
- Too high → material failure risk
Axial Grip Force (kN)
- Required press-in force
- Important for assembly process
Torque Capacity (kN·m)
- Maximum transmissible torque
- Critical for rotating parts
Hoop Stress (MPa)
- Stress in hub due to expansion
- Must stay below material yield
Example
Shaft OD: 50.05 mm
Hub ID: 50.00 mm
Fit Length: 60 mm
E: 210 GPa
ν: 0.3
μ: 0.12
delta = 50.05 – 50.00 = 0.05
👉 Result:
- Interference = 0.05 mm
- High contact pressure
- Suitable for heavy-duty interference fit
Design Guidelines
Recommended Interference Range
| Diameter (mm) | Interference |
|---|---|
| 10–50 | 0.01–0.04 mm |
| 50–100 | 0.02–0.06 mm |
| 100+ | 0.04–0.10 mm |
Fit Selection
- Light press fit → easy assembly
- Medium interference → general mechanical use
- Heavy interference → high torque transmission
Material Considerations
- Steel: high stiffness, high pressure
- Aluminum: lower modulus, lower pressure
- Mixed materials → asymmetric deformation
Friction Coefficient (μ)
Typical values:
- Dry steel: 0.15–0.20
- Lubricated: 0.08–0.12
- Press with oil → lower force
Manufacturing Tips
- Use chamfers to ease assembly
- Consider thermal fitting (heat / freeze)
- Ensure surface finish consistency
- Avoid excessive interference → cracking risk
Applications
- Gear mounting
- Bearing installation
- Shaft-hub connections
- Automotive assemblies
- Aerospace structural joints
FAQ
What is a press fit?
A tight fit where parts are assembled using force or thermal expansion.
What is interference fit used for?
To transmit torque and prevent relative movement.
How much interference is too much?
When hoop stress exceeds material yield strength.
Can aluminum be press-fitted?
Yes, but requires lower interference due to lower strength.
Does lubrication affect press fit?
Yes, it reduces friction and required assembly force.
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- Fits & Tolerances Calculator
- Hole Size Calculator
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