No matter what causes distortion it’s gonna happen. Doesn’t matter if you let each weld cool back to room temp before continuing. Physics is physics I don’t like forced cooling because why harden the weld especially a mig weld. The key is not the heat. The key is getting the best fit possible and clean as possible. This reduces heat by keeping the weld as small as possible. The other key is proper hammer and dolly work. This is true for mig, tig, or torch.
That’s about the best way. If the patch fits nice , then you weld a little and all of a sudden it doesn’t feel or fit nice anymore you know exactly where and why to work the weld. Yokum gave me one tip when I took his and cornfield customs class that upped my game. It’s the amount of pressure used to push back with on the dolly. Roughly enough to lift 30 lbs. I was always kind of holding the dolly back there and using the hammer, and it’s really fucking hard to put that much force into a dolly then hammer into your hand. Majority of work/force goes is into the dolly and light taps with the hammer. I had it backwards.
Heat moves metal. The shrinking disc is a great example and there’s no need to debate that. Next is that welds (which are hot and)shrink and have heated the zone known as the Heat Affected Zone or HAZ also shrink. So there’s 2 sets of shrinking going on. after a weld you now have an area that is shrunk with different degrees or amounts of shrinking that is non linear. (It’s a bell curve not a slope) With Most shrinking being at the weld and less and less and less and less on your way back out of the HAZ. Watch the gap. Read the metal. Heat expands the metal and closes the gap before the shrinking happens. So it’s technically fit perfectly as humanly possible then stretched then shrunk. The longer the tack weld without stopping will have different stenches. A series of uniform tacks will each have the same change. One of those tacks if 2-3 times as long will have different change. Welding without stopping will have a very uniform amount of Change along the length of the weld. Look at the HAZ
Lots of good advice here and I'd like to add that 49Ratfink's suggestion to use an air driven cutoff disk to clean up the weld is a great one, I ground all the MANY welds on the Studebaker exactly like that, skip around to keep the heat down both welding and grinding. I know I am not a great welder/bodyman but I try to keep the use of plastic to a minimum, but I do use it
Chopped my 1969 Beetle 5" in 1992 with a MIG welder and it still lives 27 years later. Nothing wrong with MIG welding. Hennie
You just made me feel a lot better about patches and a little filler. That’s what I am doing on my ‘57.
That’s another debate. How much time do you spend on a panel to keep from using a filler? Filler can be sprayed, wiped or melted in. I aim for less than 1/8th filler less for something like a hood. The more prep you spend setting up a weld(fit and cleanliness) you get less deformation, less hammer and dolly time and usually less filler. .
I agree, I try to aim for as little filler as possible. With that being said, i by no means am a metal working professional. So sometimes the filler is a little more than I want.
A master metal guy told me masters sweat the details. Doing the basics correctly improves success. The difference between a master and a novice is usually patience.
Not a Master, but not a Novice either. I have plenty of patience too, maybe to much. Probably the reason my projects end up stalling.
40 answers all with some information based on each persons hands on work. Each depends on skill level and personal level of good enough and that makes it the right way for each of us. There is no one way or right way. But there are ways to improve your skill level.
Metal shrinks 5 to 7 times more than it expanded when it was heated, and it shrinks the same amount if it is cooled fast or slow ! Heating metal over 450 degrees will shrink it when it cools ......... End of story , that is a fact !!!! You must find a way to deal with that damage. Hammer and dolly , or mud her up ???????? . If it takes 100 hours to make a panel that is 80% of perfect . It will take 200 more hours to finish that panel to absolutely perfect ...
Well, like I said, I'm working on an OT little truck. But I had welded in a repair panel on the driver side by tacking here and there on all sides and ended up with quite a bit of distortion. So yesterday I installed the passenger side but cut the top corners at an angle, then tacked all across the top first. After the top was filled I slowly started on the sides, working my way to the bottom. While I did have some distortion, it was not NEAR as bad as the other side. I was much more happy!
I think in my own personal musings that the majority of sandblasting distortion is caused by the pressure on the panel from the high psi and CFM combined with 47 million little hammer taps of sand. Never seems to distort if the operator reduces CFM and delivery at a glancing angle.
Next time I run the shrinking disc I’ll shoot the surface temp with IR gun. I don’t think it generally gets that hot (450) and it still moves
Hail dents on dark color cars can some times be removed some , or made smaller when set in the hot summer sun for a day! The thinner the metal the less heat it takes to shrink it.
Any tricks for making rounded corners? Hole saw? Jig saw? How large should the radius be? Thanks for the tip
Gospel right there! I bought a real nice hood for my Nova years back when being painted because mine needed some work, took it to a guy to have blasted and the guy DESTROYED it, and this was after it had some work done due to a small bump in the front. It was so bad you could visually make out where it pushed against the underside bracing.
I use a quality set of shears use whatever you have for a template for the radius size you want, change, a socket........ I use a scribe or fine tipped magic marker to lat out the line for a cut then make a rough cut leaving about 1/4 inch that can be trimmed with the shears A good shear will cut a radius, I then use a file to fine tune the cut The time spent making a good fit saves time during the weld process. A better weld is easier to grind and metal finish
1/2" radi. often works just fine like the step drill 31Vicky mentioned. Depends on how the panel is shaped. I have a full set of Greenlee conduit punches that get used for all kinds of weird things. I will often use the 1" punch when doing smaller jobs. Not having a sharp corner seems to be the big deal and making the new mating part fit well. A 2" radi. seems to make the corner transition go real smooth.
HERE, nothing like watching someone while they explain what they're doing. there's a dozen good ways to do this, practice on a bunch of scrap first. good luck
This isn't about thin sheet metal, but it explains the warping caused by welding very well. If you understand HOW it happens, you have the best chance to avoid making it a problem.
Something tells me you also have a collection of different size "punchouts" saved for filling firewall holes, etc, I know I would if I had a Greenlee punch.
The Jalopy Journal
