Pre heating a panle before TIG welding.

[The_Yellow_Ardvark]

I slipped out to see a friend, spread some season cheer, his case a small bottle of spiced rum. He restores old cars for rich people.

One car they have is a 1930 Cadillac, they were fitting a new roof panel.

But as one person was TIG brazing the panel to the roof cross members his work mate was heating the other side with OA.

Why?

The area being heated with the OA was quiet small and they had damp rags about 4” either side of the work area.

Any one shed on any light on what or why they were doing it that way?

 

[mpats]

Something to do with trying to stop warping of the roof panel by evenly heating either side maybe?

 

[Mee]

Containing the heat to a specified area, and it would possibly have been how they were originally fitted at the factory depending upon its age.

 

[Ton-up]

I'd have thought the best people to have asked was them?....

 

[The_Yellow_Ardvark]

@Ton-up
They were in the welding bay, I was with my friend "borrowing" some metal off cuts and stuff.
I didn't get a chance to ask him, spiced rum etc.

But on some American cars of the 30's had a lot of panels brazed on.

 

[slim_boy_fat]

"borrowing" some metal off cuts and stuff.

How do you return them [not in kind, I understand about spiced rum, whisky etc ] - do you present him with something along these lines......

As an aside, I see those sculptures made from old spanners, gear wheels, bits of chain etc and wonder at the ingenuity of the creators. Wish I was blessed with the talent to visualise something like those, e.g........

 

[The_Yellow_Ardvark]

@slim_boy_fat
I borrow from their of cut bin, with a promise to return to them.
But with my shot term memory issues I forget, this I put down to my short tem memory what means my short tm memory.

 

[hotrodder]

There's loads of different ways to skin a cat but the only things would make sense to me are that they were either heat shrinking areas with oxy and wet rags or tinning an area that needed leading?

Damp rags (or paper mache or expensive 'cold front' putty) don't stop distortion, they just contain it to a smaller area and as a result can make it worse locally. If they were heating spots and immediately quenching them with the wet rags that'd result in highly localised shrinking and is a fairly common technique for shrinking 'tin can' spots when you can't get to the back of the panel without cutting holes in things and/or removing bracing. If they were getting ready to lead the joint wet rags would stop heat from travelling further into the roof skin and risking more distortion outside of the area to be leaded

 

[The_Yellow_Ardvark]

@hotrodder
They were OA the outside with the damp rags as the other was TIG brazing the inside.

 

[hotrodder]

Yeah, i got that. Heat shrinking or lead loading the side they'd already done or heat shrinking spots to make it fit better before brazing are the only things that would make sense to me. Sticking the new roof skin to the stiffening ribs/internal structure with modern panel adhesives or even tigerseal would make more sense to me and sidestep distortion from TIG brazing the skin to roof stiffners