You can also rent a torch set-up from a rental place. I have done this in the past and it is faily in-expensive. I would say borrow one if you can. If your cutting large sheets that thick a torch is the only way to go (besides plasma). I tried the skill saw method and although it is WAY faster than a recipricating saw it is sometimes harder to make nice cuts. And like a chopsaw it is smelly, loud and make a mess. For aluminum I have always used a skill saw with carbide blade and a jig saw. But still I say torch.
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