Does anyone know how to cut a hollow rectangle out of a steel ruler? By that I mean cutting a small part out of the standard steel ruler while having the outside part still in tact. So a band saw is out the ballpark. Its for a home project and any help would be greatly appreciated. Thanks!
Drill a round hole, and then square the sides with a file.
You might also get lucky by calling metal working shops in the area. If they have a punch of the right size, it would take only seconds for them to punch the hole for you.
A maker space might have the tools to help you here. Possibly a laser cutter.
Depending on how small a square you want to cut out, you may be able to do it with a rotary tool (e.g.- a Dremmel) with a cut-off wheel.
For the serious metalworker there are square punches, but for the hobbyist one great tool is the nibbler. This is a handheld punch that removes about 1/8 by 1/4 inch of material per stroke. With practice you can make almost any size and shape hole you want in sheet metal. I know Klein Tools makes one, as one I have one. Others probably do so as well.
You can use a scroll saw to cut it out. A scroll saw is similar to a jigsaw because it has a short, removable blade. These kind of saws are designed for very smooth and fine cuts that other saws aren't capable of.
Drill a small hole in the center of where the hole will be that is big enough to receive a scroll saw blade with a little bit of extra space. Carefully cut out the section, and cut slightly inside of the line, giving enough of a margin for finishing. Use a small to medium sized metal file to smooth out the hole, and bring it to the final dimension.
Rotary tools would not do a great job on this because the diameter of the cutoff wheels are probably larger than the hole you want to make.
Laser cutters are much more common nowadays and you may find a metal worker that can do it for you as it would take very little time at all to cut it out (~2-3s)
Another option, if there's someone nearby, would be a water jet. They work just like laser cutting only they use high pressure water, and work well for steel.
if you have access to a well supplied maker space, a water jet cutter would suit you well.