BIZOMAT MAKEOS · Quality
True Position with Bonus Tolerance
Is this hole or pin within its positional tolerance, including any bonus from its size?
Diametral true-position deviation from measured X and Y deviations, with bonus tolerance at maximum or least material condition, and size limit checks.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Feature | choice | Hole or pin. |
| Material condition modifier | choice | Modifier in the feature control frame. |
| Measured X deviation from true position | mm | Measured X location minus basic (true) X. |
| Measured Y deviation from true position | mm | Measured Y location minus basic (true) Y. |
| Position tolerance (diameter) | mm | Diametral position tolerance stated in the feature control frame. |
| Measured feature size | mm | Measured actual mating size of the feature. |
| Lower size limit | mm | Lower size limit from the drawing. |
| Upper size limit | mm | Upper size limit from the drawing. |
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.
What this means: Feature
- What it is
- Whether the toleranced feature is internal, such as a hole, or external, such as a pin or boss. It decides which direction of size gives bonus tolerance.
- Units and format
- Choose one of 2 options from the list: Hole (internal); Pin or boss (external).
- Example
- The form opens with “Hole (internal)” selected as a worked example. Choose the option that matches your case.
- Get it right
- A slot counts as internal and a tab as external.
What this means: Material condition modifier
- What it is
- The material condition symbol shown after the position tolerance in the feature control frame, or none for regardless of feature size.
- Units and format
- Choose one of 3 options from the list: MMC (Ⓜ); LMC (Ⓛ); Regardless of feature size.
- Example
- The form opens with “MMC (Ⓜ)” selected as a worked example. Choose the option that matches your case.
- Get it right
- Copy it from the drawing; with no modifier shown, choose regardless of feature size and no bonus applies.
What this means: Measured X deviation from true position
- What it is
- The measured X location of the feature’s axis minus its basic, true X location, in the drawing’s datum reference frame.
- Units and format
- Enter a number in mm: millimetres. The form accepts -10000 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.06 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Position deviation rises with the distance from the true position.
- Get it right
- Measure from the datums on the drawing; a sign error does not matter, as it is squared.
What this means: Measured Y deviation from true position
- What it is
- The measured Y location of the feature’s axis minus its basic, true Y location, in the drawing’s datum reference frame.
- Units and format
- Enter a number in mm: millimetres. The form accepts -10000 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.08 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Position deviation rises with the distance from the true position.
- Get it right
- Use the same datum frame and origin as the X deviation.
What this means: Position tolerance (diameter)
- What it is
- The diameter of the cylindrical tolerance zone stated in the feature control frame, before any bonus.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.2 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only moves the allowed position and the pass or fail line.
- Get it right
- This is a diameter zone; do not halve it. The tool doubles the radial deviation to compare.
What this means: Measured feature size
- What it is
- The measured actual mating size of the feature: the largest pin gauge that fits a hole, or the smallest ring that fits a 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 10.12 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Moving away from the modifier’s material condition adds bonus tolerance.
- Get it right
- Use the actual mating size, not one two-point caliper reading, for the bonus.
What this means: Lower size limit
- What it is
- The smallest size the feature may be, from the size tolerance on the drawing.
- 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 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It is also the maximum material size of a hole, where its bonus starts at MMC.
What this means: Upper size limit
- What it is
- The largest size the feature may be, from the size tolerance on the drawing.
- 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 10.2 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It is also the maximum material size of a pin, where its bonus starts at MMC.
Method and formulas
- Actual position = 2√(dx² + dy²).
- MMC bonus: hole = size − lower limit; pin = upper limit − size. LMC bonus: hole = upper limit − size; pin = size − lower limit. RFS: no bonus.
- Allowed = stated tolerance + bonus; the feature passes if position ≤ allowed and the size is within limits.
- Example: deviations of 0.06 and 0.08 mm give a position of 0.2 mm against 0.32 mm allowed.
Limitations
- Two-dimensional position relative to the datum frame used for measurement; datum shift (mobility) is not included.
- Uses the measured size as the actual mating size; form errors affect real gauging.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Accept or reject holes and pins from CMM or layout results
- Explain bonus tolerance to the shop
- Check a fixture or gauge design
Who it is for
- Quality inspectors
- Toolmakers
- Metrology technicians
What you get
- Actual position (diameter)
- Bonus tolerance
- Total allowed position tolerance
- Size within limits
Interpreting the result
- A functional gauge accepts exactly what MMC position allows; use it for production checking where possible.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 615–627. Topic reference; no source tables or recommended settings are reproduced.
- ASME Y14.5-2018 Dimensioning and Tolerancing
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