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Old 12-01-2012, 04:33 AM
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sheet metal welding questions

I am trying to patch in a fender lip on a restoration project. I read through the archives before attempting hoping to try and eliminate any warpage. I was 100% successful on other areas of the car (rockers, quarters etc). I couldn't have asked for a better result. However these 2 (right & left) fender lips have me stumped. In the attached photo the circled area is where I get the warp. If I cut the patch where you see the black lines, about an inch on the vertical and 1 to 2 on the horizontal the panel returns to its original shape. I am about to try a third attempt but figured I would end up with the same result. Is there some thing I can do differently to get a better result? I am using a Lincoln MIG. I have taken a ton of time to keep the heat build up at a minimum. I don't understand which way the metal is moving to try and prevent the warp. It sucks that a 2" weld can screw up a decent panel when the first 10" didn't affect it at all.
Thanks- Mark
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Old 12-01-2012, 05:38 AM
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So when you cut the panel, the gap created from the cut probably expanded a bit more than the thickness of the blade used and that allowed the panel to go back into place.

If this is the case, its telling you that you need to planish, (hammer and dolly) the weld to stretch it out some.

The metal at the weld has shrunk causing the distortion further away.

Do not tap the metal at the warped area. As you slowly planish the weld, you will see the problem disappear.
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Old 12-01-2012, 05:57 AM
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Does it matter if the weld is hot? I work alone so it's tough to tack it and then hammer. I have read that the weld needs to be glowing. Also, should I tack, hammer, let cool, and repeat? Or hammer when its all welded in?
Thanks for your help.
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Old 12-01-2012, 06:53 AM
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Planish cold.

I was under the impression it was welded twice already and was currently welded.

Do not reheat the area again is you've done it twice already. Planish (cold) along the whole weld and watch your problem area to see if it starts to pop back.
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Old 12-01-2012, 07:37 AM
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I hope it's OK if I jump in here, "123Pugsy" is correct...I will try and explain how things like this happen...when you weld, you create heat, the heat expands the metal, when it cools it shrinks more than it expanded when it was hot. So, when you planish the metal (hammer and dolly) what you are doing is stretching the metal back to it's original thickness. Think of it this way...might sound stupid but it may get the point across...when you tenderize a steak by hitting the meat, the steak gets thinner, but it also gets wider...(sorry but it's the only similarity I could think of at the time). When the metal is back to it's original thickness the warping should be minimalised. Metal has memory, but when it's heated it stretches as it cools it shrinks causing metal to loose it's memory, when you use a hammer and dolly your giving your metal a reminder as to where it used to be.

I hope this helps.

Ray
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Old 12-01-2012, 08:08 AM
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I agree with pugsy, do not make any relief cuts or do any work anywhere except on the weld itself. If you are quick enough to planish the weld while it is still hot it will reduce the chance of cracking, but that is history now that its already welded. Do not reheat.

I prefer gas or tig but in the future its important to make sure the patch fits perfect before welding, and with a mig just do a spot here and there and let them cool naturally.

When planishing cold, grind the weld bead almost but not all off the front and back, then put a dolly with a similar contour on the back side and hold it with a good amount of pressure to the weld and strike on the dolly with firm blows up and down the weld area, you should hear the ring of the hammer hitting the dolly. You will see when it starts getting close to the right contour, then start using a straight edge, and keep raising the lowest areas. Its not that difficult, you can do it, good luck.
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Old 12-01-2012, 11:19 AM
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Thanks to all!
Your tips resulted in success. Now I will be able to sleep tonight. After a 'victory" beer or two.
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Old 12-01-2012, 11:43 AM
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Glad to hear it.

Thanks for posting the results. Enjoy the pint.
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Old 12-01-2012, 12:39 PM
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Always nice to hear about a good outcome.
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Old 12-12-2012, 05:14 AM
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Allow me to jump in with a question. I've been working with scrap body metal trying to gain some kind of feel for welding in patch pannels. When I start the hammer dolly work on the patch, do I concentrate my work mostly on the weld? Is my hammer face smooth or or dimpeled?
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Old 12-12-2012, 06:07 AM
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Do your work only on the weld itself, and don't ever use the waffle face hammer or waffle face dolly for anything, they just damage your metal.
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Old 12-12-2012, 06:16 AM
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waffle face

A 28 oz carpenters waffle head is good for building houses, the theory behind a waffle body work hammer was that you could hit with a glancing blow to move metal. I don't use one. I try to keep all my body hammers polished by working them on the back side of my 6 X 48 in. belt sander
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Old 12-12-2012, 08:44 PM
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Dimpled-face tools

Quote:
Originally Posted by Chevymon View Post
Don't ever use the waffle face hammer or waffle face dolly for anything, they just damage your metal.
I've had some success shrinking oil can spots using my dimpled hammer and dolly, but they do not leave the metal silky smooth by any means. I ended up cutting this piece out for other reasons unrelated to the hammer and dolly work.
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Old 12-12-2012, 10:57 PM
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Quote:
Originally Posted by Supercharged03 View Post
I've had some success shrinking oil can spots using my dimpled hammer and dolly, but they do not leave the metal silky smooth by any means. I ended up cutting this piece out for other reasons unrelated to the hammer and dolly work.
If you have an oil can problem on a roof or any panel with body lines...I like to take a body hammer and a block of wood. Place the wood on the side of the panel and tap the wood with your hammer...your actually putting strength back into the panel and then the panel can be metal worked using a hammer and dolly. If you still have a low spot on the panel, your "waffle Hammer" will expand the metal and remove the low spot by tapping around the low spot. If I have a high spot I use a regular body hammer and dolly...always glancing the hammer in an outward direction around the high spot. In effect your moving the metal away from the high spot and giving it no choice but to straighten out.

I hope I explained this in a way that's understandable...this may be one of those things where hands on showing would be more helpful.
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Old 12-14-2012, 03:36 PM
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you can allso use a propain torch like a plumbers just heat the center of the low and cool it quich with a cold wet cloth it will shrink the metal if you do it right and stop the oil can
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