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Bending roof molding


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9 minutes ago, Mark Gregory said:

I was wondering where did you buy that roof molding as my 1931 Reo Royale needs some also.

 

Plus learning how to bend it is an excellent question.

 

 

Bought it at Snyder's Antique Auto Parts.   They sell Ford A & T parts but but it is close to what I needed.  Don't forget to get the rubber filler.  I am using 1" #4 SS pan head screws to hold it down.  Had to put the screws in a drill and take a little off the heads on the grinder for clearance. 

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I would think you would cut the piece a little long, start in the middle and attach it solidly until the first bend.  Bend it with your hand and screw it down.  Keep on until the end.  I don't think you can pre bend it.

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I have had good results softening aluminum with a hot air paint stripping gun. Also works a treat, if used carefully, to heat up die cast pot metal if it is bent and needs straightening.

 An oldtimer friend of mine ,who was a sressed skin worker in aviation industry, also told me , use an oxy torch, first blacken the aluminum using just the acetylene, then heat it up with an oxy /acetylene flame until the black just starts to dissappear. at this point stop heating and it should be soft enough to bend.

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7 hours ago, Tinindian said:

I would think you would cut the piece a little long, start in the middle and attach it solidly until the first bend.  Bend it with your hand and screw it down.  Keep on until the end.  I don't think you can pre bend it.

Thanks for the suggestions.  I agree that pre bending is not the way to do it.  Others have suggested annealing which my understanding occurs at about 775 degrees F which would be hard to do while attaching.  Because of it's shape it just wants to kink when trying to bend sideways and I need to make a couple back to back bends.  Other suggestions appreciated. 

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I agree with a plywood jig, anneal and pre bend. It's better to under bend and then adjust the radius tighter than over bend and try to adjust the radius larger. Stretching the molding making the bend is easy. Shrinking it not so much............Bob

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I seem to recall that bending a preformed aluminum lineal without kinking can be done by filling it with sand. I've never done this, but in theory, at least,  it makes sense.

Once it's packed well with sand, you would then bind the molding tightly with a narrow, strong tape...something that doesn't stretch . Annealed wire would be ideal, but time consuming unless you only did the bends. The idea is to confine the molding both internally and externally before you attempt the bend. In making a bend, you want to stretch one side of the molding, but prevent the opposite side from crimping. 

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I seem to recall that bending a preformed aluminum lineal without kinking can be done by filling it with sand. 

 

I have seen them bend steel hot water heating pipes to make an expansion loop on a high rise building 50 years ago.

But they hammered down the ends of the pipe so the sand was confined and would not move.

So I do not know how you would keep the sand in place to cause some resistance to stop the crumpling of the aluminium section.

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I’ve done quite a few GM roofs with the aluminum trim moldings sold by Bobs Buick. Because I do so many, I made up a jig with a roller bearing on a lever which allows me to bend both side, after simply changing the pattern form to the other side of my jig. I always bend the molding off the roof and where a gentle bend is needed like the sloping of the mid to rear of the roof, I pull the molding back and forth over my leg as I apply light pressure. My blue jeans add just enough friction to slightly warm the aluminum while I’m pushing it down some. The GM type molding resembles angle iron and after it’s screwed down to the car, the top of the “angle” gets swaged over.

 

 Most Automotive aluminum moldings are fully bendable as is and don’t need anealing but you will have to test yours. I would make a wood pattern in the shape of your roof and form the molding to it. It usually takes two sets of hands when forming a “one off” molding and sometimes three sets. One holds the start end fast and another can hold the other end applying pressure against the pattern. The third person uses a hardwood flat stick made to fit the molding and starts from the end working with taps of a hammer on the hardwood stick, swaging the molding to the shape of the pattern. I have learned to make my patterns slightly undersized and the bends slightly greater than the actual area. This allows for some bounce back and some elongation as it’s being formed to the pattern. When you put the molding on the roof, you want it to naturally pull itself down on the roof. 

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