Keeping it square

[savarin]

I will be welding up a bunch of steel frames and screens to screen my patio.
The design I have come up with is --

The outer frame is 35x5mm flat bar, the verticals are 10mm square.
The blue parts are bifold doors.
rather than cut the verticals in half with a possible miss alignment at the central cross piece I thought I would drill holes in it to pass the verticals through then tack each one in place top bottom and middle first and finish welding them fully in place once they are all tacked.
I'm not so worried about mild twist in the flatness of the frame as I think that will disappear once bolted in place.
What I am unsure about is the twist that may occur in that middle rail from the welding process.
Anyone any ideas?

 

[C-Bag]

The only way we were able to deal with the inevitable twist and pull was make a really heavy duty jig table out of channel iron. Careful setup of the table and measuring the frame then clamping everything to death. Maybe I'm just to cynical but I know from past experience if I welded something in place like that, it would end up in place. Period. Doors are tricky. Just my worthless 2c.

 

[Cadillac]

I’ve built acouple big Assy. like what our are planning. Definately want to make a full size jig clamping all the pieces. I would tack all the seams on one side let it cool. Flip it tack all your seams then release from the jig and see where it moves. Then I would pick the worst spots and do a full weld opposite of the bow to pull it back. A good tack may be all it needs for the interior pieces full welds might be to much depending on gauges of material. Frame should be fully welded though. Jig will help for keeping everything aligned and the same.