Bodywork dish

[Russell Reay]

I just finished welding in the lower cowl panels and subrail extensions, and now have a 1/8" dish --front to back- in the original panel above the weld. The new left panel is flat, but the right new panel is high at the door pillar, firewall and in the middle, but dished 1/4 of the way in from each end. What is the best way to 'pound out' these dishes?

[40-A Twins]

The metal shrank wherever it was heated by your weld, so it needs to be stretched out using hammer and dolly along the length of the weld. I had to hammer a door skin over a sandbag to bump out a large dent, then use the shrinking disk to smooth out all those hammer marks.
Kevin

[Russell Reay]

The sandbag is a good idea, but what is a shrinking disc?

[Dave1931Pickup]

Check out this site:
https://www.wolfesmetalfabrication.com/sdisc.html

[40-A Twins]

I bought a 9" shrinking disk from Wolfes and got pretty good at using it to smooth down those stubborn bumps that just won't go away with simple hammer and dolly work.
The disk generates heat via friction and shrinks the bump down until it is level with the surrounding area. The only trick is that you have to get access to the high side of that bump with disk / grinder tool, either from the back side of the panel or by bumping it out to the outside. Using the shrinking disk I can get the metal much closer to original form and use less bondo than before.

[Harpkatt]

Sponsored Links (Register now to hide all advertisements)

Shrinking can also be done with a torch, but is less easily controlled and more likely to overheat and over shrink the panel. Practice is needed to get good with either. The shrinking disc is slower but seemingly more and more favored.

[Kevin in NJ]

So the problems are multifold.

First off, was the patch panel flat that you put in place? Most store bought one are. You need to first put in the compound curve found in all cowl sides. Please bear in mind I have not done many 28-29 types and that was a very long time ago.

Every weld is a shrink point. The correction is to do hammer on dolly hits to stretch the metal. This is made impossible if you did an overlap weld. Only works for butt welds.

The size of the shrink is dependent on how large the heat affected zone is. More heat, more shrink to correct.

MIG welding sucks. You need to first use a flap sanding disk to level the weld then you can hammer it. Usually the MIG area is a bit harder and not level enough to hammer on dolly and have it nice.

Take a piece of paper and tear the middle of an edge about 1" and then overlap it slightly. You will see the paper form a bump. That is what happened. The correction is to either shorten the whole paper or stretch the edge.

DO NOT TRY TO HEAT SHRINK to correct this problem. I can tell you from experience it will only make it MUCH worse. This was bad advice from old timers I tried following. You would think a guy with 50 years experience knows stuff, but he did not. I learned to not follow any of his advice. Once I learned how to shrink and stretch metal my patches got much better.

Once I got a TIG I found I could do patches and not see the weld lines in the bare metal. I did a few spot welds and then hammer on dolly corrections. You MUST wait until metal temps equilize to know if the panel is ready. If one area is slightly hotter you can be trying to fix distortion that is not there. Yes, I did that once, and only once. Patience is key and probably the hardest lesson of doing metal work.

[Oldbluoval]

There are great YouTube videos on shrinking and other metal work. Wray Schelin’s are good and Wolfe’s. I also use a Stinger to shrink in specific spot; comes with special head. Just takes getting used to.
Agreed MIG welding is problematic but quick and easy. Very short learning curve; TIG is a longer learning curve.
Another great process is the use of slapping spoons on small “bag of walnuts” areas where prior “body men”, used loosely, have used a pick hammer to knock a dent out!

[old ugly]

the weld sucked the panels in. hammer on dolly on the weld to relieve it. first step and see what happens.

in the old days we would wet paste with powdered asbestos wetted into a paste on either side of the area to be welded to try to control heat transfer. but. it seams there is no more asbestos, its a shame.

if needed, don't fear the filler.

ou