BIZOMAT MAKEOS · Fasteners
Taper Pin for Torque Transmission
What mean diameter of taper pin through this shaft and hub transmits the torque safely?
Mean taper pin diameter needed to transmit a torque (or power at a speed) through a shaft by double shear, by the handbook formula, with the shear stress in a chosen pin.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Load given as | choice | Enter the torque directly, or power and speed. |
| Torque | N·m | Torque to transmit (torque mode). |
| Power | kW | Power transmitted (power mode). |
| Speed | rpm | Shaft speed (power mode). |
| Shaft diameter | mm | Shaft diameter at the pin. |
| Safe shear stress of the pin | MPa | Safe shear stress for the pin material (with your safety margin). |
| Pin mean diameter to check (0 = none) | mm | Mean diameter of a proposed pin. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Load given as
- What it is
- Whether the load on the pin is given directly as a torque, or as a power and shaft speed from which the tool works out the torque.
- Units and format
- Choose one of 2 options from the list: Torque; Power and speed.
- Example
- The form opens with “Torque” selected as a worked example. Choose the option that matches your case.
What this means: Torque
- What it is
- The twisting moment the pin must transmit between the shaft and the hub or collar it locks. Used only when the load is given as torque.
- Units and format
- Enter a number in N·m: newton-metres. The form accepts 0.000001 N·m to 10000000 N·m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 N·m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The pin diameter needed rises with the square root of the torque.
- Get it right
- Include any shock or service factor; a pin is often meant to shear as a safety device, so check the intended failure torque too.
What this means: Power
- What it is
- The power flowing through the pinned joint, used with the speed to find the torque. Only used when the load is given as power and speed.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 100000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use kilowatts; the motor nameplate power is a common starting point if the joint carries full motor output.
What this means: Speed
- What it is
- The rotational speed of the shaft at the pin, used with the power to work out the torque. Only used in power mode.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 1000000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 500 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- At constant power, a lower speed means more torque and a larger pin.
- Get it right
- Use the speed of this shaft, which differs from motor speed after a reduction.
What this means: Shaft diameter
- What it is
- The diameter of the shaft where the cross hole for the pin is drilled. The pin shears at the shaft surface on both sides.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger shaft lowers the pin diameter needed, with the square root of the diameter.
- Get it right
- Use the shaft diameter at the hole, not at a larger shoulder nearby.
What this means: Safe shear stress of the pin
- What it is
- The shear stress you allow in the pin material, already reduced from its shear strength by your chosen safety margin.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 10000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The pin diameter needed falls with the square root of the safe stress.
- Get it right
- If the pin is a shear pin meant to break at overload, size it from the material’s shear strength and the break torque instead.
What this means: Pin mean diameter to check (0 = none)
- What it is
- The mean diameter of a taper pin you are considering, halfway along its length in the shaft. Zero skips the check of a chosen pin.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Shear stress in the checked pin falls with the square of its diameter.
- Get it right
- Taper pins are listed by their large-end diameter; work out the mean diameter where the pin crosses the shaft.
Method and formulas
- d = 1.13 √(T ÷ (D S)) with T in N·mm, D in mm and S in N/mm² (the pin is in double shear at the shaft surface).
- Torque from power: T = 9549 × P ÷ n (N·m).
- Check: the force at the shaft surface, 2T ÷ D, is carried by two pin sections, so τ = 4T ÷ (π d² D).
- Example: 60 N·m through a 30 mm shaft needs a 5.65 mm mean-diameter pin.
Limitations
- Pin shear only; the cross hole weakens the shaft and the hub bearing stress must be checked.
- Use a safe stress with a margin for shock.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a cross pin fixing a hub or collar to a shaft
- Check an existing pin after a power change
- Choose between a pin and a key
Who it is for
- Design engineers
- Maintenance fitters
What you get
- Mean pin diameter needed
- Shear stress in the checked pin
Interpreting the result
- Taper pins are good for light to moderate torque; use keys or splines for heavy drives.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 220, 1714–1720. Topic reference; no source tables or recommended settings are reproduced.
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