How to Check the Radius on a Curved Segment.

If you have a curved segment that is less than 180 degrees, you need geometry to verify the radius because you can’t directly measure the diameter.

Begin by selecting an appropriate straight edge to use as the chord—the longer the chord, the more accurate the measurement.

Push the straight edge up to the inside of the curve.

At the middle of the straight edge, measure the distance from straight edge to curve—called “rise on chord” or “mid-ordinate.”

Use the geometry:  Radius = ½  (rise² + ¼ chord²) / rise.

The image below shows the use of a 36” chord to “spot check” parts.

I measure 23/32” (0.719)  so Radius = 1/2 (.719^2+.25*36^2)/.719 = 225.7

Or you can enter this info into the radius calculator on our website.

Are you interested in where this formula comes from?  Simple derivation shown here:


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