Fabrication question

[Thebeast]

Hi if this is posted in the wrong area I am really sorry as I didn’t know what category this would come under.

I have attached photos of the problem. So on the first pick on the left side of the box section I put a tri square and it is showing that it’s pretty much bang on 90 degree and then when I put the tri square on the other side it’s out.. any idea on what’s causing this?

Thank you for any answers greatly appreciate any help

 

[Welderpaul]

The piece on the bottom has deflected upwards or is bent

 

[roofman]

The piece on the bottom has deflected upwards or is bent

yea you can see the deflection in it.

 

[Thebeast]

The piece on the bottom has deflected upwards or is bent

What would cause that to happen?

 

[Morrisman]

What would cause that to happen?

I’d say the lower tube was already bent before you started. That little tack wouldn’t do it.
But when you fully weld it it will, unless you clamp the lower piece to something solid.

 

[roofman]

I would check with a longer straight edge against further up the box section...might be plumb at the top.

 

[brightspark]

take it back off and use a strait edge to check if the bottom piece has deflected or bent as said in post 2

 

[voipio]

Also check that the try square is accurate. Put a good straight edge over some paper, and use the try square to draw a 90 degree line, perpendicular to the straight edge, then flip the try square over and draw the line again. If the 90 degrees is true, then the two drawn lines should be parallel.

What I've seen of Blue Spot tools so far, is that they're not bad, but they are made down to a price.

 

[Thebeast]

Also check that the try square is accurate. Put a good straight edge over some paper, and use the try square to draw a 90 degree line, perpendicular to the straight edge, then flip the try square over and draw the line again. If the 90 degrees is true, then the two drawn lines should be parallel.

What I've seen of Blue Spot tools so far, is that they're not bad, but they are made down to a price.

This is a nice idea I will try this out! Thank you

 

[Ed.]

RHS is notoriously bad for not being straight. SHS is much better, once you fully weld the circumference it will really bend up, you can use that to your advantage to a certain degree, just place a thin piece of steel under where the area where you will weld from above above and force a bit of a reverse curve in the bottom beam by clamping the ends down, and after the weld is done, release the ends of the clamped bottom RHS steel and it might pull the reverse curve back straight.

It probably was bent during transport or storage. I have seen bundles of RHS dropped on to the curb from a flat bed and also 8m lengths lifted by a forklift in the middle and the ends just bend, sometimes the steel will straighten out sometimes not, or else kept stored without enough supports

 

[Ed.]

RHS is notoriously bad for not being straight. SHS is much better,

Oops, got that in reverse RHS stays straighter than SHS provided you weld on the thinner side. As an example if you have a 100x50mm SHS, it will resist bending more if you weld on the 50mm side as the 100mm sides will help it from bending. Help is the important word here as it will still try to bend but not to such a degree.