Originally Posted by sailah
What's the difference though when you join the parts together? It's still a butt joint or am I missing something? I can make one of those dollies easy enough and the actual forming doesn't look difficult at all.
Basically, it's a question of managing where the material flexes -- if it's a square corner, and the flat sheet "drums" (i.e. vibrates up and down in the middle), the welded corners will be where it flexes. That's why square welded corners break.
If you put some shape into the corners, it flexes where it's tangent to the large, flat area, and leaves the weld alone.
It's also a good idea to bead roll some stiffening "X" shapes into the large flat areas to prevent them from drumming in the first place.