There was more interest than I expected on the aluminum tanks. Seeing as how this is the "Fabrication and Techniques" forum, I figured I'd do a ride-along on my next tank so folks could see how I did it, and maybe glean something.
So this is what I start with. A pile of bent and machined parts.
First thing I do is make sure everything is deburred and there is not any dross from the laser on the edges. Nicholson makes a super nice file cut for aluminum. I just run this on the edges of the sheet quick to take off any burrs.
I then start fitting up and tacking the side panels to the top structure.
I shoot for an outside corner joint, and if it doesn't immediately match up, a trick I use is to take a thin piece of sheet metal and use it as a little lever to slip the edges into alignment.
Once I get it where I want it, I hold it with my torch hand, and make a tack.
If I have the opposite problem, the gap is too wide, I make a quick tack across the gap, and tap it into alignment.
I work my way around the tank, tacking every 6 inches or so.
Once I am all tacked up, I weld the seams. I do 6 inches or so at a time, skipping around the tank to evenly distribute the heat.
Once the tank itself is welded out, I attach the mounting tabs, hose bungs and filler neck. I plan to make a fixture to locate the tabs, I just haven't gotten around to it. It doesn't take that long with a tape measure and combo square.
I hold it in place with a bar clamp to get it tacked up.
This is the trickiest part. The tacks have to be fast. If I linger too long, the sheet heats up too much and pushes away from the bracket. I focus the heat on the bracket until I get a small puddle, then I quick wash it down onto the sheet.
I tack all the brackets, bungs and the filler neck first before I weld them. It gets too hot to try and measure and fuss with a bracket to tack it when you've just welded the bracket 6 inches away.
The filler neck has to be at a slight angle, mostly for looks but to make it easier to add gas. The angle itself isn't critical, just needs to be there. I use my 3rd hand tool to hold the filler neck wedged at an angle to get some tacks on it.
I then weld out the brackets first.
Then the bungs. I use a TIG finger from Jody at Welding Tips and Tricks at this point. Very hot. I also use a kevlar hot glove to rest my hand on in some places.
The last thing I do is weld the filler neck in. Its enough thicker than the sheet that I give it a few seconds of pre-heat with a plumbing torch.
Done and ready to be delivered to the customer.
Thanks for looking.