[s-neff]

You can do flat weldments laid out on plywood (with dummy shafts to preserve hole alignment). This was on 192, doing welded drivetrain module frames. As long as the board was flat, we didn't even really need to put much vertical constraint on the pieces - just using a pneumatic nail gun to put wood blocks in to hold everything in place was fine. We'd tack weld one side, then flip it over in the same jig to tack the other side, then finish the welds outside the jig. Some rework occasionally required for warp. All student welds, what do you expect.

On the Mini-Baja race car team in college, we ended up designing 3/4" particleboard jigs for the tube chassis with waterjetted cutouts in the exact design locations for each tube, and laying everything out before welding. It helped that we were using the same particleboard that our tube sponsor packaged the pieces with for transport (free), and that our waterjet time was free from the ME department in return for help with the upkeep.