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  #21  
Old 03-13-2018, 07:18 PM
cliffrod cliffrod is offline
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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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  #22  
Old 03-13-2018, 11:28 PM
bobadame bobadame is offline
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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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  #23  
Old 03-15-2018, 09:17 AM
Sprint Relic Sprint Relic is offline
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I love math
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  #24  
Old 03-20-2018, 05:38 PM
Payupv8 Payupv8 is offline
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Quote:
Originally Posted by bobadame View Post
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.


Attachment 46032

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I reall Like this gauge very cool idea, I wonder how hard it would be to duplicate, I had to put this fender project to the side for a bit to repair some rusty doors for my friend and Iam starting an e wheel build. I also plan to make one of those flexible profile gauge
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  #25  
Old 03-20-2018, 09:13 PM
bobadame bobadame is offline
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A couple of things I'd do differently with this tool. First, the data would be more accurate if the 3 legs ended as a sharp point instead of the .062 radius which they have now. The radius, even as small as .062 introduces a chord length error which gets worse as the tool is used over a tighter radiused surface. Since dragging points across a painted surface isn't practical, I'd probably make the legs have a larger radius but then I'd mill half of the radius away so that instead of a point at the end there would be a vertical plane exactly at the centerline of each leg. Also, I'd place the 3 legs at 120 degrees apart on a 2" radius. These changes would give a more accurate chord length. Unfortunately though it would tend to average the radii of converging surfaces.

Another Idea I'd like to explore would be to replace the analog indicator with a digital one with an output datalink to a PC. And maybe a mouse to map X and Y location on a grid which could either be projected or drawn onto a surface. There should be a switch on the tool which would tell the PC to create a point and record X,Y, and Z data at each intersection on the grid. This might be a simple way to digitize a curved surface close enough to determine the shape of buck stations.
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Last edited by bobadame; 03-20-2018 at 09:20 PM.
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  #26  
Old 03-22-2018, 03:32 PM
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schönheit der arbeit schönheit der arbeit is offline
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Take a lock in this older tread too .

http://www.allmetalshaping.com/showthread.php?t=994
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