



 
Ayman, You will have to measure something, so you might as well measure the radius directly, as curvature. I have seen gauges in the form of metal arcs or discs that can be fitted to the inside of a curve to make such a measurement, but I have no idea where to buy them. You could make your own set (sheet aluminum? light plywood? plastic?) easily enough. 45 degree sectors at whatever radii you come across in your work would work well. For big radii (10cm or more) you could cut out "rainbow" shapes a couple cm in width. My understanding is that bending jigs for pipe, etc. often come with interchangeable inserts so that one jig may make more than one radius of curve. If you are using such a jig you could try placing these inserts against the inner curve of the pipe and see which one comes closest. Good Hunting!
 


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