KEVOS® MAKEOS · Gears
Gear Chordal Thickness and Addendum
What chordal thickness and chordal addendum should a gear tooth caliper read?
Chordal tooth thickness and corrected (chordal) addendum for measuring spur gear teeth with a gear tooth vernier caliper.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Module | mm | Module of the gear. |
| Number of teeth | teeth | Number of teeth. |
| Addendum (0 = one module) | mm | Addendum; 0 uses the standard one module (enter the actual value for shifted or stub teeth). |
| Arc tooth thickness at pitch circle (0 = standard π m ÷ 2) | mm | Circular tooth thickness at the pitch circle; 0 uses the standard π m ÷ 2 (enter a thinned value to include backlash allowance). |
Method and formulas
- Pitch diameter D = m z; half-angle θ = t ÷ D (radians).
- Chordal thickness tc = D sin θ (= D sin(90°/z) for standard teeth).
- Chordal addendum ac = a + (D ÷ 2)(1 − cos θ).
- Example: module 3, 30 teeth: set the caliper depth to 3.0617 mm and expect 4.7102 mm across the tooth.
Limitations
- Measures from the tip, so tip diameter errors affect the reading; span or over-pins methods are more accurate.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Inspect cut gears with a gear tooth vernier
- Set up gear cutting depth
- Check worn teeth
Who it is for
- Gear designers
- Machinists
- Maintenance engineers
What you get
- Chordal tooth thickness
- Chordal addendum (caliper depth setting)
- Pitch diameter
Interpreting the result
- Correct the depth setting by half the difference between measured and nominal tip diameters.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2145, 2238–2240. Topic reference; no source tables or recommended settings are reproduced.
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