This will be a long section with a lot to read, but I believe it will be worth it. There will be pictures, too. This will amount to a rudimentary metalworking tutorial on annealing and bending aluminum molding.

I knew the molding was going to be tough. The thing is, when you bend a piece of molding - or even solid bar or round stock, you have to deal with geometry. You take a thing that is one inch thick, and bend it. You create a curve... whether sharp or gradual, it doesn't matter. The line on the outside of the curve is going to be longer than the line on the inside of the curve - but it is all the same piece of metal - or wood or plastic, or whatever. The material on the outside of the curve has to stretch, and the material on the inside of the curve has to compress. If the material is not allowed to stretch and compress, it will tear or break or collapse in some way. In the case of molding, it will twist in such a way that its internal stresses are minimized or balanced.

My source of aluminum was a local "handyman supply" outfit 30 miles away. There was a good selection of hot rolled steel shapes and extruded aluminum goods. The aluminum was "hard" which meant that it would really resist bending and would have to be annealed.

Annealing

To anneal something is to soften it, whether to relieve stresses or to make the material easier to work with. Ferrous materials, like mild steel or carbon steel are annealed by heating it to a critical temperature and then allowing it to cool as slowly as possible. The slower, the softer. Insulation or controlled heat is sometimes used to really slow down the cooling. Non-ferrous materials like copper and aluminum are just the opposite. The metal is heated to a critical temperature and then quenched to cool it very quickly. Copper is fairly easy, because you can see what temperature it is by seeing what color light it gives off. Go to a dull red heat. Aluminum, on the other hand, will melt before you see any obvious color change (unless you are in a dark room.) The first visible light you will see is a very dark red, at about 900 to 1000 degrees F. Aluminum will melt about 1100-1200 degrees F. To further worsen things, aluminum is "hot short" which means in practical terms that it has very little tensile strength just before it lets go of itself. I was heating a piece of molding to anneal it, and I figured I was at the right temperature and maybe just a few more seconds to make sure ... and then the end of the molding just fell off with no sag or bending or anything and the end was not showing signs of melting it just let go uffda.

So, what do you do? How do you know when it is time to quench? I only got two hands, jeepers! Work in a dim, subdued light. Assuming you are using a propane torch with a clean bluish flame, you will see a suggestion of a slight rosy character to the light in the flame next to the metal. Quench it now, do not tarry longer here! Some will use a candle and "smudge" the aluminum with candle soot here and there. As the aluminum is heated, the soot will sorta burn away or vaporize, or do what soot does at a certain temperature, and the aluminum will be hot enough to quench. I used my Sharpie marker to make some marks on the aluminum every couple of inches in the area I wanted to anneal, and when those marks faded away to near nothing, the metal was ready to quench. I started doing this outdoors, being harder to set the house on fire if I had a fit of clumsiness or a lapse of attentiveness. I had the garden hose at hand for the quenching and all I had to do was shut off the torch, set it down, grab the hose and quench. Safe, satisfying, and messy. Later, when it was too cold to do this outdoors, I was forced to work over the laundry tubs. This actually turned out to be better. I rehearsed my moves so I knew where the torch was, where the flame was, and where the laundry tub hose was. It was also dimmer light in the basement, so I could more easily see the change in the color of the torch light - (though not quite soon enough one time.) I marked the area I wanted to anneal, and heated the metal. When the marks from my Sharpie disappeared, I shut down my torch, and quenched the molding. No bending over, no fumbling around for the hose or a safe place for the torch, and the water spray was mostly confined to the laundry tub. If you are of a technical bent, you can get a "Tempilstik" at a welding supply shop. It is a crayon which will melt at a particular temperature. Get one for about 500-550 degrees. If you have one of those infra-red instant reading temperature guns, you could use that. Again, I would go for about 500-550 degrees. Lamp-black, candle soot, and black Sharpie pigment vaporize or oxidize about 450 degrees, I think.

The bending and the pounding

I made a bending jig to get my molding close to the shape I wanted. I had decided that I wanted doors with round corners rather than mitered square corners. The wisdom or rationality of the decision aside, this is what I wanted. I knew it was going to be extra work, but being a stubborn cuss, I made my choice and accepted the aggravation.

The doors were to be about 2 feet by 3 feet, with 6" radius round corners. This would give a circumference of just under ten feet, which would work well with the molding. The molding comes in 20 foot lengths, and I had them cut to 10 foot lengths so they would be easier to bring home from Duluth.

The basic routine was to clamp the annealed molding to the jig and then bend it around the corners. The reality is in the details, though. I did not have a large enough shop to clamp the jig down, so I had to wrestle with the jig and the flopping-around molding and not kink it or smash a light fixture or lose my balance or my temper. Once the molding was bent to all four corners, the molding also had an unhappy looking twist to it in the corners, as expected. (Some of this could no doubt be reduced a bit with a better fitting roller on my bending jig, and more room in my shop, and accommodation for more clamping on the jig itself. My own skill was not quite adequate, either, and this was likely the main factor.) My next step was to clamp a block of wood with the 6" radius curve to my work bench, and then clamp the molding to the block of wood. Successive bouts of pounding and clamping and more pounding eventually stretch and flatten and reshape the molding to the shape it is supposed to have, and I can proceed to the next corner. Once the molding was subdued and pounded to a nice smooth flat curve in each corner, I used another plywood form very close to the size of the door for another round of clamping and pounding. At this stage I could trim the overlapping molding ends to a good approximation of the final size. Depending on how much work you are doing to the aluminum, you may also be work-hardening it. You may have to re-anneal it, before going on. I had to do this a couple of times on the galley hatch molding.

When the doors were paneled and skinned with sheet-metal, I could fasten the molding to the door itself. I used a white silicone caulk to seal the molding to the door, so this was a messy job. I drilled and countersunk holes in the molding 6" apart and 1/8" past the apparent middle along the length of the molding. It was easy to tell what part of the molding was annealed and what part was hard. The countersink flutes would fill with swarf (little metal shaving bits) in the annealed areas. I'd have to stop often and clean the countersink, then cut a bit more - stop, clean, cut, and so on, until the countersink was deep enough. In the hard parts of the molding, the countersink would cut smoothly, and a nice spiral shaving would flow out of the flutes until the cut was done. The cut surface was also very shiny. As an aside, I did not drill and countersink the holes until after the bending was done, so the molding would not have weak spots in it every six inches.

The molding is clamped in place at each corner, to minimize twisting, and also to keep the molding corners where they are supposed to be. I should have fastened some sturdy clamping block to each corner where you see pairs of C-clamps in the photo. The fourth corner is not yet bent, but there will be clamps there, too.

This is a view of the roller I made for helping bend the molding. The roller is set up in this case for bending a piece of outside molding for the doorway in the trailer. I had a little too much slack between the roller and the radius block, and the molding was able to twist out of shape - but not quite as bad as the first piece I bent without any roller at all. In addition, the roller and the clamps help restrain the molding so it does not kink.

A block of wood with the desired radius is clamped to the workbench. The bent molding is clamped to the block. The molding is hammered to shape against the block. Not shown is a block of hardwood with the end beveled to a 90 degree angle and at a 45 degree angle to the length of the block. This was used as needed to refine the 90 degree angle in the molding in the bend. Please make sure that the block of wood is at least an inch longer than the width of your hand. Don't ask.

This is what a hot-short failure looks like. I felt that I needed to re-anneal a piece of molding, and was a bit slow on the quench. Notice I also had the holes drilled in this piece. I discontinued pre-drilling the holes before the bending process. The failure was right across a hole, and I thought maybe the molding was just slightly weaker here. Maybe not. In any case I had no more hot-short failures.

I have begun fastening the bent molding to a finished door. There is an overlap, so I marked where I thought I should trim. I lifted the molding up high enough to clear the door, and then put a block of wood under the molding. I then clamped the whole works so it would not move while I hacksawed the molding. I had to repeat the process, to remove another eighth of an inch. uffda.

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