KEVOS® MAKEOS · Quality
Bolt Circle Pin Check (Pitch Circle from Plugs, Readings at the Limits, Decision)
For a ring of equally spaced holes measured over plugs, what pitch circle diameter does my reading give, what readings should I expect at the limits, and does it pass?
Inspection of a bolt circle (pitch circle) of equally spaced holes with close-fitting plugs: the pitch circle diameter from a micrometer or caliper reading over two alternate or adjacent plugs and the size across opposite plugs (as the bolt circle over plugs tool), the readings that correspond to the nominal pitch circle and its tolerance limits, and the accept or reject decision.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Number of holes | holes | Number of equally spaced holes. |
| Plug (hole) diameter | mm | Diameter of the plugs fitted in the holes. |
| Measured over | choice | Whether the reading is over two plugs with one hole between (alternate) or two neighbouring plugs (adjacent). |
| Measurement over the plugs | mm | Reading over the outsides of the two plugs. |
| Nominal pitch circle diameter | mm | Pitch circle diameter on the drawing. |
| PCD tolerance (±) | mm | Plus-or-minus tolerance on the pitch circle diameter. |
Method and formulas
- Alternate plugs: PCD = (m − d) ÷ sin (360° ÷ n); adjacent plugs: PCD = (m − d) ÷ sin (180° ÷ n) (as the bolt circle over plugs tool).
- Across opposite plugs = PCD + d for an even number of holes.
- Reading at a pitch circle = PCD × sin + d, at nominal and at each limit.
- Example: the reading gives a PCD of 100.02 mm (nominal reading 96.603 mm).
Limitations
- Equally spaced holes; the reading checks the circle, not the spacing of each hole.
- Plug clearance in the holes adds directly to the error.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Inspect the PCD of a flange or hub hole pattern
- Set up a go/no-go reading for a hole circle
- Check a drilled pattern before tapping
Who it is for
- Inspectors
- Machinists
- Quality engineers
What you get
- Pitch circle from the reading and size across
- Readings at nominal and the limits
- Decision
Interpreting the result
- Measure several pairs round the circle: a spread between pairs shows a spacing or roundness error, not only a size error.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 686. 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.
