If you're ready to join two waterjet or laser cut parts together at 90 degrees to each other, you have a few good options.
Welding will work, but comes with its own difficulties, including the fact that it requires a welding machine and the skill to use it.
To join flat parts at right angles using only fasteners like nuts and bolts, read on.
This technique can be done with common hardware store nuts and bolts. It occupies little space, except where the nut protrudes from the plate. The hardware is partially exposed, which can make assembly easier, but is less elegant looking than using nutstrip (described below) and leaves the hardware vulnerable to being bumped out of place.
Another popular option for joining plates at 90 degrees is to use nutstrip. This handy hardware is a square bar of aluminum with tapped holes at 90 degrees to make it easy to stick two parts together. You can cut it to length with a hacksaw to get just the right amount of hold.
One disadvantage of nutstrip is that it does occupy some space in the corners where your plates come together. On the other hand, it is very handy for lids and access panels, as you don't have to worry about the nutstrip falling out while you screw it in from the outside as it's held in place to the other panel. Read more about using nutstrip.
Got any other ideas for joining flat parts together at 90 degrees? Let us know!