KEVOS® MAKEOS · Quality
Bolt Circle Inspection from Three Holes (Fitted Diameter, Centre Position)
From the measured centres of three holes on a bolt circle, what diameter and centre do they actually lie on, and are the circle size and its centre position within tolerance?
Inspection of a bolt circle from three measured hole centres: the circle through the three points, its centre and diameter (as the circle through three points tool), the deviation of the diameter from nominal, and the position of the circle’s centre from the datum origin as a diametral position value (as the true position tool, regardless of feature size), against the diameter tolerance and position tolerance, with a check of how widely the holes are spread.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Hole 1 X | mm | Measured X of hole 1 from the datum origin (the datum bore centre). |
| Hole 1 Y | mm | Measured Y of hole 1. |
| Hole 2 X | mm | Measured X of hole 2. |
| Hole 2 Y | mm | Measured Y of hole 2. |
| Hole 3 X | mm | Measured X of hole 3. |
| Hole 3 Y | mm | Measured Y of hole 3. |
| Specification | ||
| Nominal bolt circle diameter | mm | Nominal bolt circle diameter. |
| Diameter tolerance (±) | mm | Plus-or-minus tolerance on the bolt circle diameter. |
| Position tolerance of the circle centre (diameter) | mm | Diametral position tolerance of the pattern centre relative to the datum. |
Method and formulas
- Circle through three points: centre from the perpendicular bisectors, radius to any point (as the circle through three points tool).
- Diameter deviation = 2r − nominal.
- Centre position = 2√(c_x² + c_y²) from the datum origin (as the true position tool, regardless of feature size).
- Example: the holes lie on 100.03 mm (+0.027648 mm) with its centre 0.042354 mm (diametral) from the datum.
Limitations
- Three holes define the circle exactly, so hole position errors show up as circle errors; more holes need a best fit.
- Measurements in the drawing’s datum reference frame.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a drilled flange on a CMM or height gauge
- Find the actual pitch circle from hole coordinates
- Check the pattern centre against a datum bore
Who it is for
- Inspectors
- Quality engineers
- Machinists
What you get
- Fitted centre and diameter
- Diameter deviation
- Centre position and spread of the points
Interpreting the result
- Pick three holes spread at least 120° apart; close holes make the centre very sensitive to errors.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 40–48, 615–627. Topic reference; no source tables or recommended settings are reproduced.
- ASME Y14.5-2018 Dimensioning and Tolerancing
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.
Open the Bolt Circle Inspection from Three Holes (Fitted Diameter, Centre Position) calculator
