KEVOS® MAKEOS · Power Transmission
Ratchet and Pawl Design (Pitch, Tooth Force, Bearing and Pin)
What pitch and diameter does this ratchet wheel need for the torque, what force does the pawl take, and are the tooth face and pawl pin strong enough?
Design of a ratchet and pawl holding a torque: circular pitch at the outside diameter by the handbook crane-ratchet rule and the outside diameter (as the ratchet wheel pitch tool), the tooth force at the outside diameter, the bearing stress where the pawl tip meets the tooth face, and the shear stress in the pawl pivot pin, against your allowables.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Torque held | N·m | Torque the ratchet must hold. |
| Face width of the teeth | mm | Width of the teeth (and of the pawl tip). |
| Safe stress for the ratchet rule | MPa | Safe stress used in the handbook ratchet rule for the material (your value; low values for cast iron). |
| Number of teeth | Number of teeth on the ratchet wheel. | |
| Pawl engagement depth on the tooth face | mm | Depth of the tooth face the pawl tip bears on. |
| Allowable bearing stress on the tooth face | MPa | Allowable bearing (contact) stress between pawl and tooth. |
| Pawl pin diameter | mm | Diameter of the pin the pawl pivots on. |
| Pin shear planes | choice | Whether the pin is in single or double shear. |
| Allowable pin shear stress | MPa | Allowable shear stress of the pin. |
Method and formulas
- Circular pitch P = √[F M ÷ (L S N)] with the tooth-number factor F (as the ratchet wheel pitch tool); outside diameter D = P N ÷ π.
- Tooth force at the outside = 2M ÷ D; bearing stress = force ÷ (L h).
- Pin shear = force ÷ (planes × π d² ÷ 4).
- Example: a 16-tooth wheel needs a 29.58 mm pitch (150.65 mm outside); the pawl takes 2,655.1 N.
Limitations
- Static holding torque; shock engagement can multiply the load several times.
- Pawl body bending is not checked.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Design a ratchet backstop for a winch or hoist
- Check a pawl pin for a higher torque
- Choose tooth count and width for a ratchet
Who it is for
- Design engineers
- Machine designers
- Maintenance engineers
What you get
- Pitch and outside diameter
- Tooth force and face bearing stress
- Pawl pin shear stress
Interpreting the result
- More teeth give finer engagement but a smaller pitch: the face width must grow to keep the bearing stress down.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2215–2217, 1535. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Ratchet and Pawl Design (Pitch, Tooth Force, Bearing and Pin) calculator
