KEVOS® MAKEOS · Power Transmission
Ratchet Wheel Tooth Pitch
What tooth pitch and outside diameter does a ratchet wheel need to hold this turning moment?
Circular pitch of ratchet wheel teeth at the outside circumference for holding a suspended load, from the turning moment, face width, safe stress and number of teeth with the handbook’s tooth-number factor, and the resulting outside diameter.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Turning moment on the ratchet shaft | N·m | Torque the ratchet must hold. |
| Face width (ratchet thickness) | mm | Width of the tooth face. |
| Safe stress for the tooth material | MPa | Safe working stress you allow for the ratchet material, reduced where shock loads occur. |
| Number of teeth | Number of teeth on the wheel. |
Method and formulas
- P = √(F M ÷ L S N), with M in N·mm, L in mm and S in MPa.
- F = 50 for 12 teeth or fewer, 35 for 13 to 20 teeth and 20 for more than 20 teeth (handbook).
- Outside diameter = P N ÷ π.
- Example: 200 N·m on a 16-tooth, 25 mm wide ratchet needs a 29.58 mm pitch.
Limitations
- Crane-design rule for holding ratchets; check the pawl, its pin and the hub separately.
- Shock loading needs a lower safe stress.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a ratchet and pawl for a winch or hoist
- Check an existing ratchet against a higher load
- Choose tooth count and face width together
Who it is for
- Machine designers
- Lifting equipment designers
- Maintenance engineers
What you get
- Circular pitch at the outside
- Outside diameter
- Factor used
Interpreting the result
- A wider face or a stronger material reduces the pitch and wheel diameter.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2215–2217. Topic reference; no source tables or recommended settings are reproduced.
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