[JesseK]

I think it's actually alot easier than most people think to keep things square and precise while welding. The biggest success we had this year was the fact that we had a perfectly square and flat frame on the first try. Our student build team captain took a bit of time to consider everything that was needed before welding and came up with a plan for manufacturing the frame. We didn't start welding until I and (more importantly) the professional welder at our sponsor approved the plan.

When we welded our drive train frame together, we also brought in threaded rods that matched the axle holes and a bunch of nuts to fit the rod. We then spaced out the frame on the rods and welded the outer rails to the rear cross support. Then we used precisely-cut wooden blocks as spacers, and clamped the inner rail to the outer rail with the spacers in between. We measured diagonals as well as across the gaps before we welded, then after we spot-welded, then again after the final welds. Since the rods and spacers were firmly in place, the frame could not bend/warp.