[TheForge] Warped!

[Ries Niemi]

Kirsten-

  your flat bar
(not strap- I know you are very precise in calling your materials and 
tools by their proper names, in your work- this helps communication in 
all fields)
is warping in the middle, right? And my guess is that is because of the 
welding of your tree in the middle.
Miters and clamps would help you make a frame that was flat. But in and 
of themselves, they wouldnt help when you add that tree. Well, miters 
wouldnt. Enough clamps probably would help. Miters and clamps would 
help you make your initial frame flat and square, but you add another 
layer of potential problems when you start putting your art into the 
middle of it.
The thing is, even though 3/8" seems like hefty stock, it isnt very 
resistant to bending when heat is added, especially in the "easy " way, 
which is how I understand it to be bending.
  Best solution is to add minimum heat, while clamping the flat bar down 
to a heavy steel table, which will also help to dissipate heat. I would 
tig weld this together, while the 3/8" flat bar was clamped down with 
something like a visegrip 11R C clamp style right on either side of the 
weld. Another way to minimise heat input would be to tig braze- you tig 
weld, but use a silicon bronze filler rod. Since you are only brazing, 
you dont need to heat the material up anywhere near as much. This could 
be a problem if you object to the brassy color of the filler rod, 
however. But it works really well on thin to thick connections- I used 
to make a production piece with 24 ga steel welded to 3/8" steel, and 
the tig brazing was a lifesaver.
You dont specify what welding technique you are using, but obviously 
some put a whole lot more heat in than others.

A couple of other techniques used in extreme cases- sometimes I will 
prebend a piece opposite of how it will warp when welded.
And sometimes, on very fussy stuff, you can actually submerge the piece 
in a tank of water, with only the actual weld zone out, and then heat 
warpage is almost nil.
Other profiles of material that are more resistant to bending is 
another possible solution- the reason picture frames resemble angle 
iron in profile is the "L" shape is much more resistant to bending than 
flat bar is. So either using angle instead of flat, or laminating a 
flat to a smaller angle behind it, would both increase resistance to 
bending quite a bit.

ries