Technical Metal Bending Math-Help Needed

I'm trying to create a roll pan for the rear of my Model A coupe using only hand tools. So far, its 20 ga. steel formed into a squared "C" shape -so a flat panel with a 90 fold along the top and a radiused 90 fold along the bottom-both along the long axis. I now need to bend the ends in a curve to match the round corners at the back of the body and I know I'll have to make cuts in the 90 degree folds so that they don't crimp, then weld the cuts to finish it.

What I could use help with is figuring where to make the cuts in the "arms" so that the metal of the "body" of the C will be smooth. Does anybody have a formal for doing this or advice on how to proceed? Thanks in advance

 

i think that is going to take trail and error and some educated guesswork...that's what i'd do

 

Tagboard. Make a mockup of the part from heavy paper, and see what happens. But you might decide to "shrink" the folded edge instead of cutting notches in it, you can do this by making it wavy, using pliers or something. Another thing you could to is to cut round shapes out of it instead of notches, and don't go all the way to the bend, maybe stay 1/4" away.

 

I just did the same for my 46, but I have a shrinker. It did not take much to get a radius. I would make or buy some sort of crimping pliers instead of cut/weld. I would also start with a short piece with a 90 bend as a test for crimp spacing and sneak up to it. I started with shrinking lightly 2" apart and that was close.


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You may try this, take a tape (a seamstress tape works well) and measure along the radius from the top of it to the bottom of it on the A body panel, or any other radius you are trying to match in the future. That gives you a linear dimension for the amount of metal it will take to create your radius.

 

In Ron Fourniers book "Basic Metal fab" he goes thru the process of making what you describe.
If memory serves it was 3 piece where there was the back roll pan and then made the ends to attach. that way one can just screw up an end and not the whole thing. He is a top fabractor and found this to be the best way.

 

Thanks, guys. Guess I need to do some trials and reading. I bet there's a mathematical way to figure it out, but I have no idea,yet.

 

http://img06.deviantart.net/b34d/i/...las___ps_brush_set_by_soulrebel83-d15vjl7.jpg I thought this was it but it's for figuring out how many toothpicks you get from a 20 foot tree! (sorry I,m a wise ***) Pete

 

I used to work for a company building precision sheet metal ch***is for computers. There is a formula for "Bend allowances" but it never was totally accurate because of variations in material and the actual bend. We would make our "Blanks" using the formula but always had to fudge a little to get the exact measurements. That required making some samples first. I think for your project I would make a extra long "C-channel". Then starting with the middle section, mark where the bends need to be. After the bends are done I would cut off or finish the ends the way you want them.

 

Math don't work so good when it comes to floor pans.
Try using some heavy paper they put down to protect floors and build yourself a pattern.