KEVOS® MAKEOS · Fasteners
Taper Bush Grip Check (Screw Preload, Wedge Normal Force, Torque Capacity)
For a split taper bush pulled into a hub by its screws, what grip does it put on the shaft, and will it carry the drive torque without slipping?
Check of a taper-lock (split taper) bush or keyless taper clamp: the preload of each tightening screw from its torque and nut factor and its share of proof load (as the bolt torque and preload tool), the total axial force, the normal force on the taper from the wedge action with friction on the taper face, and the friction torque on the shaft at the bore, against the drive torque from power and speed with a service factor.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Number of tightening screws | screws | Number of screws that pull the bush into the hub. |
| Screw nominal diameter | mm | Screw diameter. |
| Screw pitch | mm | Screw pitch. |
| Screw tightening torque | N·m | Torque applied to each screw. |
| Nut factor K | Nut factor for the screw (lubricated or dry). | |
| Screw proof strength | MPa | Proof strength of the screws. |
| Taper and shaft | ||
| Taper half angle | ° | Half angle of the taper (taper bushes are commonly about 4°–8°). |
| Friction on the taper face | Friction between the bush and hub tapers. | |
| Shaft diameter | mm | Diameter of the shaft. |
| Friction between bush and shaft | Friction between the bush bore and the shaft (clean, dry surfaces). | |
| Duty | ||
| Power | kW | Power transmitted. |
| Speed | rpm | Shaft speed. |
| Service factor | Factor for starting and shock torque. | |
Method and formulas
- Screw preload = T ÷ (K d) (as the bolt torque and preload tool); axial force = screws × preload.
- Wedge with friction on the taper: normal force = axial ÷ (sin α + μ_t cos α).
- Grip torque = μ_s × normal force × shaft radius; drive torque = 9549 P ÷ n × service factor.
- Example: 20 kN axial gives 69.514 kN of grip; 182.47 N·m capacity against 72.443 N·m.
Limitations
- Normal force taken as acting fully on the shaft; bush stiffness and the hub fit take some of it.
- Clean, oil-free surfaces; oil or grease on the bore greatly reduces the grip.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a taper bush pulley on a motor shaft
- Find the screw torque for a keyless taper clamp
- See why a taper bush slips
Who it is for
- Maintenance engineers
- Design engineers
- Millwrights
What you get
- Screw preload and axial force
- Normal force and grip torque
- Against the drive torque
Interpreting the result
- A smaller taper angle multiplies the grip from the same screws, which is why taper bushes use shallow tapers.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1521–1535, 169–171. Topic reference; no source tables or recommended settings are reproduced.
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Open the Taper Bush Grip Check (Screw Preload, Wedge Normal Force, Torque Capacity) calculator
