KEVOS® MAKEOS · Power Transmission
Keyed Shaft and Hub Design
How long must the key be to carry this drive, does the hub fit it, and is the keyed shaft strong enough?
Design of a parallel-keyed shaft-to-hub connection from the power and speed: design torque with service factor, force at the shaft surface, key length for shear and for crushing on the half-depth bearing face, the effect of a second key, the hub length needed, and the shaft torsional stress against 75% of the allowable as the handbook recommends for keyed shafts.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Power | kW | Power transmitted. |
| Speed | rpm | Shaft speed. |
| Service factor | Service factor for shock and starting loads. | |
| Shaft diameter | mm | Shaft diameter at the key. |
| Key width | mm | Key width (from the key standard for the shaft size). |
| Key height | mm | Key height. |
| Hub length available | mm | Length of the hub bore. |
| Keys | choice | One key, or two keys at 180° (assumed to share the load at 75% effectiveness). |
| Allowable key shear stress | MPa | Allowable shear stress for the key material. |
| Allowable crushing stress (weakest of key, shaft, hub) | MPa | Allowable bearing (crushing) stress of the weakest of key, shaft and hub. |
| Allowable shaft shear stress (unkeyed) | MPa | Allowable shear stress for the shaft without a keyway. |
Method and formulas
- T = P ÷ ω × SF; force F = 2T ÷ d.
- Shear length L_s = F ÷ (w τ); crushing length L_c = F ÷ (h ÷ 2 × σ_c).
- Two keys: required length ÷ 1.5 (each key assumed 75% effective).
- Keyed shaft: τ = 16T ÷ πd³ against 75% of the unkeyed allowable (handbook rule for a standard keyway).
- Example: 15 kW at 1450 rpm on a 40 mm shaft needs a 18.522 mm long 12 × 8 key.
Limitations
- Uniform load along the key; long keys (beyond about 1.5 d) carry load unevenly.
- Fatigue and fretting of keyed joints need separate attention for reversing loads.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a key for a pulley, gear or coupling
- Decide between a longer hub and a second key
- Check a keyed shaft after a power increase
Who it is for
- Design engineers
- Maintenance engineers
- Power transmission engineers
What you get
- Design torque and force at the shaft surface
- Key length for shear and crushing
- Hub length and keyed shaft stress
Interpreting the result
- If the key would exceed about 1.5 shaft diameters, use two keys, a spline or a shrink fit instead.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2460–2486, 301. Topic reference; no source tables or recommended settings are reproduced.
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