I think I am doing it wrong - heat shrink

[MG David]

So Dawai, what you are saying is I am getting too small a temperature shift.

If I have understood you correctly, either:

1) I carry on using water to cool, in which case I need to get the metal much hotter, or
2) I carry on using hot air, in which case I need to cool it much colder.

I will try 2) first as it should be less disruptive to the coatings on the reverse of the panel. All I need to do it find liquid CO2 in a can. What is that sitting on the back of my MIG welder!! I guess a little bit of argon won't hurt.

[Dawai]

Not sure about the argon temp. It sure ain't liquid going to the tig.

As others said.. "PROVEN" to you methods work best. THIS is all somebodies else's demonstration of a technique to shrink metal on youtube. I've saw some pretty amazing "special effects" on there. It is not always reality.

As Oldgoaly said, (Terry).. you need a "small" heat affected area.
Look to the "dent pulling" welder post here on MM. That might work best for a one sided repair.

I posted the video just to show another method of shrinking, not to mess you up. It's the big heat swing that shrinks metal with temperature change.

Everything is different in each situation.. I watched the "paintless repair " on youtube and can safely tell you.. I can't.. I'd have to learn a bunch of new techniques to do that.. Nor have I tried this dry ice method.

[Dawai]

Look to this post on using a "stud welder" to heat and pull-dents out.
http://www.metalmeet.com/forum/showthread.php?t=10050

A mig produces enough power, but it is rough on it. I used my lincoln mig to tig weld stainless for a couple of years, it was a old transformer model, not a current control one with transistors like the new ones... a mig has a voltage of 20-36 normally and amperage of 10-80..

a "spot welder" has a amperage of 3-800 amps and 1 1/2 volts normally.
I'll be building mine over the next few weeks.. My HF spot welder overheats after the second weld.

[beatamax]

Google spray duster for co2 in a can, you need to turn the can upside down. There is also plumbers freeze spray, you can get that from b&q.

[MG David]

beatamax, thanks.

I had looked at adverts for air dusters but they seemed to imply compressed air which will not have the same effect as CO2. Pipe feezing spray looks like a great idea. I will give it a try tomorrow night.

[Dawai]

DOC, a crazy Californian biker told me about a guy who had a mustang door crumpled.. he heated it with a rosebud and sprayed it with a Co2 Fire extinguisher.. he said you could hear the metal scream as it shrunk. (he said, she said.. I didn't see it myself) Normally he is 100% true blue thou.

Warning, working metal too "fast" causes cracks, work hardening, tempering.
And yes.. I'd not try something new on something I loved.