KEVOS® MAKEOS · Strength
Interference Fit Limits Check (IT Grades, Least and Most Interference, Torque, Stress)
With the hole and shaft tolerances I have chosen, will the fit still hold the torque at its least interference, and will the hub be overstressed at its most?
Check of an interference fit over its full tolerance range: the hole and shaft tolerances from the IT grades for the size (as the ISO tolerance grade tool), with a basic hole and your shaft lower deviation; the least and most interference; contact pressure and holding torque at the least interference against the torque times your slip factor; hub stress and safety factor at the most interference; press-in force and heating temperature for assembly at the most (as the press and shrink fit tool).
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Nominal interface diameter | mm | Nominal diameter of the fit. |
| Hole tolerance grade (basic hole, lower deviation 0) | choice | IT grade of the hole (basic hole: the hole’s lower deviation is zero). |
| Shaft tolerance grade | choice | IT grade of the shaft. |
| Shaft lower deviation (your fit) | µm | Lower deviation of the shaft from nominal for the fit you want (positive for an interference fit; from your fit standard). |
| Hub, shaft and materials | ||
| Hub outside diameter | mm | Outside diameter of the hub. |
| Shaft bore (0 = solid) | mm | Bore of a hollow shaft. |
| Engagement length | mm | Length of the fit. |
| Coefficient of friction at interface | Friction coefficient at the interface. | |
| Hub elastic modulus | GPa | Elastic modulus of the hub. |
| Hub Poisson’s ratio | Poisson’s ratio of the hub. | |
| Shaft elastic modulus | GPa | Elastic modulus of the shaft. |
| Shaft Poisson’s ratio | Poisson’s ratio of the shaft. | |
| Hub yield strength | MPa | Yield strength of the hub. |
| Required safety factor on hub | Safety factor you need on hub yield. | |
| Hub expansion coefficient | µm/(m·K) | Expansion coefficient of the hub for shrink assembly. |
| Assembly clearance when heated | mm | Clearance wanted when the heated hub is slid on. |
| Duty | ||
| Torque to transmit | N·m | Torque the fit must transmit. |
| Safety factor on slip | Safety factor against slipping. | |
Method and formulas
- IT values from the standard tolerance unit i = 0.45 ∛D + 0.001 D for the size step (as the ISO tolerance grade tool); hole 0 to +IT_h; shaft ei to ei + IT_s.
- Least interference = ei − IT_h; most = ei + IT_s.
- p = δ ÷ {d [(k_h + ν_h) ÷ E_h + (k_s − ν_s) ÷ E_s]}; holding torque = μ p π d² L ÷ 2; hub von Mises stress, press force and heating ΔT = (δ + clearance) ÷ (α d) (as the press and shrink fit tool).
- Example: interference 20.02–60.612 µm; it holds 1,061.4 N·m at the least and the hub has a factor of 1.6498 at the most.
Limitations
- Thick-cylinder theory; long hubs and stepped shafts concentrate stress at the hub ends.
- Surface smoothing reduces the effective interference slightly; allow for it with fine finishes ignored.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose a shaft tolerance for a press-fitted gear or coupling
- Check a fit over its whole tolerance band
- Set the heating temperature for shrinking on
Who it is for
- Design engineers
- Machine designers
- Maintenance engineers
What you get
- Hole and shaft limits, least and most interference
- Pressure and holding torque at least interference
- Hub stress, press force and heating temperature at most interference
Interpreting the result
- The tolerance band must keep both ends working: enough grip at the least interference and no yield at the most.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 631–634, 635–668. Topic reference; no source tables or recommended settings are reproduced.
- ISO 286-1:2010 Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes
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