BIZOMAT 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). |
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.
Round pin and hole 1
What this means: Hole 1 minimum
- What it is
- Smallest permitted size of the hole that fits on the round pin (its lower limit). It is checked against the largest pin so the part will always load.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Hole 1 maximum
- What it is
- Largest permitted size of the hole on the round pin (its upper limit). With the smallest pin it gives the worst-case clearance.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10.015 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Round pin minimum
- What it is
- Smallest permitted diameter of the round locating pin, its lower limit after wear allowance.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 9.985 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Round pin maximum
- What it is
- Largest permitted diameter of the round locating pin; it must not exceed the smallest hole.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 9.99 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Diamond pin and hole 2
What this means: Hole 2 minimum
- What it is
- Smallest permitted size of the second hole, the one that fits on the diamond pin.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Hole 2 maximum
- What it is
- Largest permitted size of the second hole on the diamond pin; with the smallest diamond width it sets that pin’s clearance.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10.015 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Diamond pin locating width minimum
- What it is
- Smallest locating width of the diamond (relieved) pin, measured across its round lands.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 9.985 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Measure across the lands, in line with the two pins, not across the relieved flats.
What this means: Diamond pin locating width maximum
- What it is
- Largest locating width of the diamond pin across its lands; it must not exceed the smallest second hole.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 9.99 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Geometry and tolerance
What this means: Pin spacing
- What it is
- Centre distance between the round pin and the diamond pin.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 300 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Wider pin spacing reduces the rotation the clearances allow.
What this means: Distance from the round pin to the feature
- What it is
- Distance from the round pin to the feature being machined or positioned.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The rotation error at the feature grows in proportion to this distance.
What this means: Feature position tolerance (diameter)
- What it is
- Diameter of the positional tolerance zone of the feature, from the drawing.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.15 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- The full zone diameter, not the radius.
What this means: Share of tolerance allowed for locating
- What it is
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 1% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 50% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Type the percentage, not a fraction.
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.
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Open the Fixture Locating Error from Pin and Hole Clearances calculator