I have some elliptical tube roughly 2 3/4" high and 6" wide at the end, with walls roughly 1/8" thick. I'd like to be able to cut it so as to get a neat, square cut, but I don't have access to a metal bandsaw. Any tips?
Rent or buy a 5" diameter right angle disk grinder. Buy a 1/32" or 1/16" inch thick cutoff wheel for it. Mark the perimeter well and cut all the way around. Clean up with the solid grinding wheel.A 4inch wide bench mounted belt sander can be used to square up the end if you cut it oversize or uneven. Go slow in order to prevent overheating the metal. Always wear recommended eye protection. You can pick up Chinese made right angle grinders for $20. Practice with it and you should be able to make square cuts. You will likely need plenty of cutoff wheels. Never twist the cutoff wheel in the cut as it may shatter.
Wrap a sheet of paper around it so it lines up, and transfer that line to it. Cut with standard hack saw. Use some lubricant. Jig saws and recip saws with metal blades will also work. Use a file or belt sander to dress the cut so it is smooth and square. If it is Al you can cut it on a table saw with a sandard wood blade, a very slow feet, and then it can rock and jam. So it isn't something to take lightly. Cut-off wheel as mentioned is also fine though it can over heat heat treated metals.