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Old 03-13-2018, 07:18 PM
cliffrod cliffrod is offline
Join Date: Dec 2014
Location: Spartanburg, SC
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As mentioned previously, a straightedge will help determine when a straight part ends and a curve begins. After those points are clarified, you can start any necessary faired curve vs true radius deliberations...

As far as transferring such information accurately between unseen surfaces, in the studio I regularly use a small cross or "X" of tape. The pieces of tape are applied face to face to each other. Stick it to one part. Clearly punch/Mark the point to be transferred in the center of the "X". Then put the other part against it so the sticky surfaces facing up stick to this other part. Carefully separate them, leaving the tape "X" stuck to this other part and the information will be accurately transferred.
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Old 03-13-2018, 11:28 PM
bobadame bobadame is offline
MetalShaper of the Month Feb 2015
Join Date: May 2009
Location: Fort Collins, Colorado
Posts: 1,077
Default chord height measuring device

This is the chord height measuring gizmo that I mentioned yesterday. The first picture shows the indicator being zeroed on a flat surface. Second picture is of the bottom of the unit. Last picture shows a reading of .102" chord height on a small fender. Using a chord height calculator that I found on the interwebb. that value equates to 11.08" radius. The design radius for the fender was 11.25". I over did it a bit with the shrinker.

I also used it to measure the top of an old 2002 BMW. The results were both good and bad. First the good, the indicator makes it possible to locate the exact point at which the surface radius begins to change. It also indicates whether the surface is a constant radius or sort of a French curve. So this device could be used to map the surface by locating the points at which the major constant radius ends and another radius begins. To map a French curve type of surface, a flexible tape like a dress makers tape could be placed on the surface along a line and chord height measurements could be taken every inch or two along that line to develop a spline curve.

The bad, on a large radius such as the top of a sedan with a radius in the neighborhood of 130" for example, a difference of .001 equates to difference of 10 to 12". So it's a bit like looking for an elephant with a microscope. One would need to check over a broad area and average the readings.

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Last edited by bobadame; 03-13-2018 at 11:34 PM.
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Old 03-15-2018, 09:17 AM
Sprint Relic Sprint Relic is offline
Join Date: Sep 2013
Location: Mesquite, TX.
Posts: 58

I love math
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