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Old 12-27-2003, 10:32 PM
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Question Question on welding patch panels?

I know that when people TIG weld they hammer on the welds as they go. I have a MIG welder and was wondering if I should do the same? The reason I ask, is because awhile back I welded in a patch panel that was about 8 inches long and 3 inches wide. When I was finished grinding down my welds, the patch panel had sunk in some. I was told that I should have hammered on the tack welds with a dolly behind them as I went, since they shrink when they cool off. I always thought that MIG welds were to hard to hammer on. I need to weld in another patch panel in a different area and it is about the same size as the last one I did. I don't want it to sink in like the last one. Any help you guys could give me would be greatly appreciated! Thanks in advance!

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Old 12-28-2003, 05:06 AM
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You are right about mig welds being to hard to hammer. You can do it with TIG and also with oxy welding, but not MIG.

When you tack welded the pannel in, i assume you spaced out the tacks, to minimise the heat - tack one corner, then tack the oposite corner, and so on. Well when you grind, you apply the same principal, grind a little bit on one side, then move to the other side.

Moving the grinder around lots will lessen the chance of it distorting. Also realise, that you aren't going to get it perfect and it is ok to use a light coat of bog, to smooth things out.

Good luck.
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Old 12-28-2003, 08:07 AM
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I agree with SlantSix. It sounds like you allowed the panel to get too hot and it warped a little. It always pays to take your time when welding in patch panels. A little extra heat can cause a lot of extra work.

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Old 12-28-2003, 10:21 AM
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Sometimes after welding in a patch that has distorted, I use a torch and then hammer and dolly it back in shape. A little mud wont hurt anything if it is applied right, it will stay as long as the metal does. I also use cold compressed air.

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Old 12-28-2003, 09:21 PM
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It is difficult to weld in a patch and Not get some distortion of the surrounding sheet metal, but it can be done with a minimal of distortion spacing the welds out to 1" then come back around and weld in between the orighinal welds and so on. Grind and fill as needed when finished welding.


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Old 01-04-2004, 04:19 PM
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That's interesting. I didn't know grinding the weld could also distort the panel.
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Old 01-04-2004, 05:05 PM
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38 Special.... Grinding causes heat. Heat causes distortion. I have seen many times that someone has been real careful when welding, just to end up warping things with a grinder.
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Old 01-04-2004, 05:14 PM
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I was grinding so much yesterday I burnt up my grinder. I just bought it in Nov. Fortunately it was a cheapo. I do have just a bit of distortion in a couple of spots. Not too bad though. Hopefully a little putty will take care of it. Live and learn.
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Old 01-04-2004, 07:52 PM
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Even removing old paint with a DA can warp flat panels if used in one spot to long. Grinding will do it even faster, keep it moving, and not to much pressure.

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Old 07-23-2004, 01:43 AM
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Grinding Heat Tip

Take a tip from a guy who has been a metal finisher for years and has fabricated, finished, painted and trained many a folk on metal finishing. When I am working with something like 18 guage cold roll, actually usually it is really hot rolled, anyway, use a small right angle 3" grinder. You will find a quality one like a Dotco will have better load speed than some of the cheapies for $40.00, but they will work as well. I think the biggest thing is to use-believe it or not- a coarse pad, say like a 36 grit. It takes a larger bite with less friction, thus keeping metal cooler, and keep the grinding pad ONLY on the weld bead. There should not be a grind mark on the metal until the weld is all gone, and then and only then you make a light clean up pass-1or 2 sweeps is it. An often overlooked art form most body folks seem to forget.
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Old 07-23-2004, 02:38 AM
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Doesn't take much heat to warp some of the thin metal on todays cars. Was welding up some spoiler holes on a cavalier trunk lid and all was going well and was going slow to minimize heat build up. Got to the very last one to weld up which was small compared to the other ones, and dipped in that flat panel. Result=Shrinking to get rid of oil can, hammer and dolly work, prying, bodyfiller and block sanding all because of that one sob hole. The other ones only needed a little grinding and a touch of bodyfiller. When mig welding, skip weld, take your time, and straighten with hammer and dolly as you go.
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Old 07-23-2004, 10:57 PM
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Hi Guys,
I originally wrote this in response to a similar question on the metalmeet forum. I think you will see that this method will dispell any myths surrounding the use of MIG welding, followed by common metalfinishing practices. The filler wire/rod used for MIG and TIG is both 70,000 tensile strength. MIG is slightly harder only because there is normally more material added. If done properly, metalfinishing a MIG weld is not a problem. Here are my previous posts.

You have to weld thin gauge sheetmetal much differently than you would heavier plate, even in the 1/8" range. You must weld a series of spot welds, with each one overlapping the last. I try to overlap by a 1/3 to 1/2 on each successive weld. You will also need to stop at regular intervals (not more than an inch) and stretch that area out before moving on, otherwise, it will have more distortion than you care to deal with.
You start by placing tack welds at 1" intervals to keep the two pieces in good alignment. (I'm only assuming you're butt welding, at this point.) You can then start the welding process. I prefer to start in the center of the seam and work out both directions toward the edge. You must stop and work the weld as you go though. To best do this, a 1/16" cut-off wheel works great for knocking down the proud weld bead. You want to leave just a tiny amount of weld above the surface, because you're going to work this down some as you hammer the weld to stretch the metal back out. You only work within the Heat Affected Zone or HAZ as we often refer to. This is the blued area around the weld. Do not leave the area when stretching a weld. Even though the surrounding area is distorted, it is still unharmed. It's just sucked in/down some when the metal shrunk along the HAZ. It will pop right back into place when you stretch the weld seam. You stretch it by hammering on dolly, in other words, you place a dolly on the backside of your weld and hit it with a hammer, making sure your hammer blows are against the dolly (or post dolly if you have one) This will rapidly stretch the area drawn in by the heat and relieve the panel of the stress caused by the heat, removing the warpage. You can now add another series of adjoining spots and continue the process, jumping back and forth from side to side, working ever closer to the edges of the panel until finished. Once you've gotten the weld completed, you can go back and fine tune the weld seam, working the panel with a slapper and dolly, producing a very smooth panel. I prefer to use a file to work down the final few thousandths of proud weld, rather than a grinder that will remove too much material. A shrinking disc will come in real handy too, to shrink any areas that you overstretched. I plan to replace a lower section of a '39 Ford fender tonight. I'll document the process and enter it here.
Good Luck

--------------------------------------------------------------------------------

This is the right rear fender for a '39 Ford Sedan. It had previously been repaired (Uh, Hmm. I mean butchered) by another so called bodyman. Also pictured are the 19ga. repair panels I shaped for the repair.


The botched previous repair has been removed and the new panel tack welded.


Here is a close up so you see that the butt joint is very tight. Also notice that I've chamfered both the replacement panel and the original fender. This is a tip from Wray that proves to work great. No problem with burning through and penetration is excellent


As I mentioned in my previous post, I try to overlap each successive spot weld by 1/3-1/2. This picture doesn't show it as well as I had hoped, but I think you can make it out if you look closely


Here is the weld seam after running a complete series of 1 inch overlapping spot weld segments, followed by stretching along the Heat Affected Zone as mentioned in the previous post.


Once I have it roughed in on the exterior side, I remove the proud weld bead from the inner side and further planish the weld seam with a slapper and dolly, carefully bringing up the low spots and filing away the remaining few thousandths of proud weld bead. I then run over the entire repaired area with a shrinking disc to remove any overstretched spots. Here are the results. No body filler will be needed, the panel is stress free, and there will be no worry of seeing a seam or early paint failure, common to lapped repair procedures.


Randy Ferguson
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Last edited by Randy Ferguson; 07-23-2004 at 11:31 PM.
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Old 07-24-2004, 12:15 AM
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Excellent post Randy. That is the type of craftsmanship we all strive for. I do however disagree about the finshing method. I know for a fact that with a 3" right angle, I can and have often ground to withing .005" by hand. I then like to finish up the rest with a palm type DA. Again these are industrial metal working type quality tools that I have made a living with. But then again you have a point since I am the only person in the plant who managed do that, so maybe a file is best for hobbyist. I am intersted in how you determine a piece of metal is in need of replacement, that is omitting the obvious rust dents etc. I have often ran into sections that seem solid enough but may be slightly weakened form some surface rust. A real common problem on sections like the top of rocker panels that I have seen. They appear to be probably about 18 gauge to start with.
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Old 07-25-2004, 01:21 AM
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Ron,
How can you "disagree" with using a file instead of a grinder to remove the the last couple thousandths of proud weld?? I think what you're implying is that you simply use a different method. The proof's in the puddin'!! If you get excellent results using your method, GREAT!!! There's certainly nothing wrong with that. The problem is, that some guys don't know how to properly run a grinder and end up cutting almost through the entire thickness of the metal. I can, and sometimes do, use your method, but I posted this message on the metalmeet forum in response to a complete novice, so I went with the safest route in teaching him and other beginners how to do this without ruining all they had strived for. They's a hundred ways to skin a cat!! There are no rights or wrongs if we all end up with as near perfect results as we possibly can...... agreed?!!

Randy Ferguson
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Old 07-26-2004, 11:58 PM
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Randy,
I stated in my post that not all people can do that kind of work with an angle grinder like the 3" I was talking about. A file is probably best for most. I just wanted to make the point that sometimes a grinder has its merit,and that craftsmanship is the key. Notice that I said in a prior post that when grinding, there should be no grind marks on anything but the weld until the last pass. For example, an excellent method for a novice on steel is to grind down a weld to about the last .010 , and then take a brown (coarse) scotchbrite disc and finish off the surface. For accuraccy, I prefer a medium hard back up disc on a Dotco 3" right angle. I have spent years microfinishing flat welded stainless panels to a mirro finish. There is no room for error, and we use grinders for productivity reasons. I have tried to train many people, and many..many, maybe most cannot even begin to do that kind of work. I respect your work because I do have an idea of the level of craftsmanship it takes. I just think that it is more important to develop skill with whatever tool you use, and a small grinder has its place even in the finest metal finishing. I would love to hear any techniques that you may have on shrinking stainless steel as I am always open on that one. It has been an expensive headache for years.
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