While some may make a mock-up of the tank first usin' the above method (construction paper/cardstock) then use those cut outs as templates, there will always be some variance between the model and the real-life tank - mostly due to the difference in thickness between the cardboard and the sheet metal, particularly in the corners. With that in mind I'll be using the metal side plates to fit the top and bottom, mostly because of the curvature of this tank. If you've not made something like this before - then you'll defo wanna make a "cardboard" tank first and use that for templates.
So - the first step is obviously to make a trace template like I did in a previous post, then simply tape the template to the steel and outline it usin' a Sharpie. If you put the bits o'tape only where there's a straight line - they're easy 'nuff to put in afterward with a ruler. Be very careful when making the marks tho as they'll be your only guide while yer cutting. Also don't
ever use the panel you just cut to trace the next, always use the template - while you would think that would result in a near perfect copy of the first cut panel, in fact you'll just be amplifying the errors in the first one and adding more;
Ya prolly noticed I'm using a simple jigsaw with a "bi-metal" blade, essentially the same as a hacksaw blade. Inexpensive and easy to use - know that no
tool (other than an industrial stamp machine) is going to be terribly accurate at this stage, so you'll want to cut on the outside
of the line, never coming within 1/16" of your "final" edge. This will be your "buffer zone" of error and blade wander - something jigsaws are famed for. You'll also want to keep your cutting area as close to the table as possible - the vibration of the tool gets amplified by the sheet to the point where the blade will "springboard" out of the cut, best case scenario it's just annoying - far more likely what will happen is you'll dent/distort the panel and will hafta start over. While you could
try and flatten it back out - it will never be the same so yer better off making another.
If you make the long cuts first then trim off the ends, you wont get that twisted off end that happens with a long cut... well, you will - but it wont be anywhere near where you care about so it doesn't matter heh, or you could be clever and put a squeezeit clamp on the tailing end to support the cutoff. Here's the panels all cut out - while I always stayed outside the line (actually I cut half the line off... but I've done stuff like this before) you can see the slight wavering and inaccuracies inherent in the tool... and me actually lol, so the next stage is to clamp the two best together and grind down to the inside
of the line - this way they'll be smooth and almost perfectly flush with each other, as close to symmetrical as I'm gonna get;
That "X" denotes the one I didn't like as much and will serve as a backup/test piece. Again, it's best to not get too attached to any one bit as it's simple enough to make another that's better. That lil rule of thumb will save much frustration and will result in a far better end product than fussin' over some lil screw-up. They first attempt at something is always the sloppiest so why worry? Heck - I may well make a second entire tank if I don't like the first, if I get a better idea - or if I just don't like the welds, recognizing yer own limitations is a valuable skill - that way ya can always work around 'em FTW