KEVOS® MAKEOS · Quality
Arc Radius from Measurement over Rolls
What radius does this concave or convex gauge or part have, from a measurement over two rolls?
Radius of a large concave or convex arc from the distance over two equal rolls and the height of the arc above the surface plate, by the handbook construction.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Arc | choice | Concave gauge resting on the rolls, or convex arc resting on them. |
| Roll diameter | mm | Measured diameter of the two equal rolls. |
| Measurement over the rolls | mm | Outside distance over both rolls. |
| Height of the arc above the plate | mm | Height from the surface plate to the arc (top of a concave arc, lowest point of a convex arc). |
Method and formulas
- Half the roll centre distance cb = (L − D) ÷ 2.
- Concave: ce = H − D; ab = (cb² + ce²) ÷ 2ce; R = ab + D/2.
- Convex: ce = D − H; ab = (cb² + ce²) ÷ 2ce; R = ab − D/2.
- Example: 20 mm rolls 120 mm over, arc 40 mm high: R = 82.5 mm.
Limitations
- Rolls must touch the arc on its true radius, away from its ends.
- Small heights make the result sensitive to measurement error.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check radius templates and gauges
- Measure large radii without a CMM
- Inspect curved parts on a surface plate
Who it is for
- Quality inspectors
- Toolmakers
- Metrology technicians
What you get
- Radius of the arc
- Roll centre distance
Interpreting the result
- Use the largest roll spacing the arc allows for better accuracy.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 687–688. Topic reference; no source tables or recommended settings are reproduced.
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