KEVOS® MAKEOS · Quality
Fixture Locating Error from Pin and Hole Clearances
How far can a part shift and rotate on its locating pins, and does that fit the feature tolerance?
Locating error of a part located by a round pin and a diamond (relieved) pin in two holes: the largest diametral clearance at each pin from the hole and pin limits, the largest translation at the round pin, the largest rotation from both clearances over the pin spacing, and the resulting positional error at a feature, compared with its position tolerance.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Round pin and hole 1 | ||
| Hole 1 minimum | mm | Smallest size of the hole on the round pin. |
| Hole 1 maximum | mm | Largest size of that hole. |
| Round pin minimum | mm | Smallest round pin. |
| Round pin maximum | mm | Largest round pin. |
| Diamond pin and hole 2 | ||
| Hole 2 minimum | mm | Smallest size of the hole on the diamond pin. |
| Hole 2 maximum | mm | Largest size of that hole. |
| Diamond pin locating width minimum | mm | Smallest locating width of the diamond pin (across its round lands). |
| Diamond pin locating width maximum | mm | Largest locating width. |
| Geometry and tolerance | ||
| Pin spacing | mm | Distance between the two pins. |
| Distance from the round pin to the feature | mm | Distance from the round pin to the feature being positioned. |
| Feature position tolerance (diameter) | mm | Positional tolerance zone diameter of the feature. |
| Share of tolerance allowed for locating | % | Share of the tolerance you allow for locating error (machining takes the rest). |
Method and formulas
- Maximum clearance = largest hole − smallest pin at each pin.
- Translation at the round pin ≤ c₁ ÷ 2 (radial).
- Rotation ≤ (c₁ + c₂) ÷ (2 L_p) radians (hole 1 and hole 2 shift oppositely).
- Position error at the feature ≤ c₁ ÷ 2 + L_f × rotation; as a tolerance zone diameter, twice that.
- Example: the part can rotate 20.626″ and the feature can be 60 µm out (zone diameter).
Limitations
- Worst-case stacking; real error is usually smaller (statistical).
- Pin bending, wear and part distortion are not included.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check whether pin locating holds a feature’s position tolerance
- Choose pin sizes and fits for a fixture
- Explain position scatter on fixtured parts
Who it is for
- Quality engineers
- Tooling engineers
- Metrology technicians
What you get
- Maximum clearances
- Translation and rotation
- Position error at the feature
Interpreting the result
- Wider pin spacing reduces rotation; tighter pin fits reduce both errors but make loading harder.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3131–3134, 620–623. 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.
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