Need help on welding sheet-metal...

['68 Coronet R/T]

The kind of patch you are practicing on is the most difficult because of being a flat sheet of metal. Most of the classic car panels will have body lines formed in them to provide some stability. Those areas without body lines will have inner support structures.
If you can get this patch installed without distortion, you will be way ahead of me for sure!

 

[Yossarian]

Saw an interesting you tube video on this subject. Make patch oversized. tack it to top side of area to be patched (just enough to hold in place). Cut around perimeter holding tool at a 45 degree anlgle to minimize the gap. Tack weld while holding the two pieces of metal in perfect alignment at the edges you are tackiing at that moment. After applying enough tacks to hold your pactch. remove the cut off excess from the back side. Finish welding, planishing and grinding each tack as you go. Slow but looks really good. Have not tried it yet but as I say looks good on youtube. No more yapping, just cut to the chase:

.

 

[MP&C]

Nick, Now if you planish those tacks where you have it right now, essentially the planishing amount needed is what make the panel flat again.

For those "hidden areas", I see those as good practice for the ones that aren't. Do those as you would do your outer sheet metal and you improve your skills each step of the way. Whether that be panel fitup, trimming, tacking, planishing, grinding, etc.. It's all part of the process. Always strive for better and it becomes second nature. Speaking of trimming, here is an excellent refresher on what we've been doing wrong with tin snips...

 

[MP&C]

Saw an interesting you tube video on this subject. Make patch oversized. tack it to top side of area to be patched (just enough to hold in place). Cut around perimeter holding tool at a 45 degree anlgle to minimize the gap. Tack weld while holding the two pieces of metal in perfect alignment at the edges you are tackiing at that moment. After applying enough tacks to hold your pactch. remove the cut off excess from the back side. Finish welding, planishing and grinding each tack as you go. Slow but looks really good. Have not tried it yet but as I say looks good on youtube. No more yapping, just cut to the chase:

Some casual observations... I would not recommend any novice use a 24 or 36 grit sanding disc on a 7" disc grinder for removing welds. Too much heat generated, can't see where you're sanding, a recipe for disaster when someone sands half the panel thickness away, or worse yet, sands through. Next, if you need to reweld after grinding, turn up the heat, you are not getting a full penetration weld. And now you need to grind again.

Part of the reason we use butt welds is to duplicate the original metal "flavor and feel" so that when someone looks in the trunk or under the floor pans, they don't see a flange repair, or have to contend with ghost lines on exterior painted panels. We can effectively cut out damaged (rusty) metal, butt weld in a new section, planish/metal finish/filler as needed, and we can have an invisible repair that for all practical purposes should be a permanent repair. The patch is normally already shaped to match (in the case of repops) so that the crown of the patch matches the existing panel. (NORMALLY) Part of the reason you see recommendation to use TIGHT butt welds, is that it eliminates open area that allows any panel movement, ie: as the weld shrinks, the panel pulls together. If the crown of our patch used to match prior to welding, weld shrinking along with the panel's pulling closer together (due to the gap) is going to pull in some of the crown. If it is a flatter crown, such as the middle of a quarter panel or top of a roof/hood, it is more noticeable as the crown in these areas is normally minimal/just enough to maintain the shape, and may result in oil canning. If it is a concave crown, such as a reverse where the wheel opening flare comes outward, then the weld seam has a tendency to pull outward as it shrinks. The following pictorial shows an exaggerated crown and gap primarily so you can see it in such a small area. But it shows what happens as weld shrinkage and panel movement pull at the surrounding area. In the bottom view, the red line depicts where the crown was originally.

With tight butt welds we do need to planish in order to remove any deformation caused by shrinking, and add some stretch back into the area. This should be the extent of our planishing effort, as the tightly fitting panels prevent the panel pull from adjacent areas (that a gap allows, resulting in loss of crown). In the case of any gappage around a patch, we would need to planish even more to add enough stretch to overcome this loss of crown, or add filler as needed.


Looking at the quarter panel in the video, and welding that took place, one would expect in the case of a normal butt weld that the edges of the panels against each other will be a positive stop against any pull from adjacent areas. The only planishing we should need to do is to overcome any shrinking issues due to weld heat. While the theory looks good on paper, the angle cut did indeed close up the gap when compared to a straight cut. But it did not totally eliminate it. My concern with this type cut is that two angled surfaces do not provide the positive "stop" that a truly butted panel does in preventing panel pull from adjacent area. After the grinding process is done, checking the weld seam with a 6" ruler may show how flat that single weld is, but our main concern should be the crown across the entire patch to see if it has pulled inward causing a loss of crown. A defect such as that will be a pain to correct, filler or otherwise. I'm not intimately familiar enough with the method to say this will indeed be a concern. But these thoughts are more cautionary, to give you things to be aware of, to look for.. if you do give this method a try.. For the quarter panel, I would expect any shrinking/panel pull to cause the following issues to the crown:

…..and to a lesser extent, the slight crown from front to back, as the weld shrinks, will pull slightly inward. Armed with this theory on shrinking and panel pull, these are merely things to look out for. More planishing perhaps may be needed to remove any defects that might show up.

 

[Yossarian]

Some casual observations... I would not recommend any novice use a 24 or 36 grit sanding disc on a 7" disc grinder for removing welds. Too much heat generated, can't see where you're sanding, a recipe for disaster when someone sands half the panel thickness away, or worse yet, sands through. Next, if you need to reweld after grinding, turn up the heat, you are not getting a full penetration weld. And now you need to grind again.

Part of the reason we use butt welds is to duplicate the original metal "flavor and feel" so that when someone looks in the trunk or under the floor pans, they don't see a flange repair, or have to contend with ghost lines on exterior painted panels. We can effectively cut out damaged (rusty) metal, butt weld in a new section, planish/metal finish/filler as needed, and we can have an invisible repair that for all practical purposes should be a permanent repair. The patch is normally already shaped to match (in the case of repops) so that the crown of the patch matches the existing panel. (NORMALLY) Part of the reason you see recommendation to use TIGHT butt welds, is that it eliminates open area that allows any panel movement, ie: as the weld shrinks, the panel pulls together. If the crown of our patch used to match prior to welding, weld shrinking along with the panel's pulling closer together (due to the gap) is going to pull in some of the crown. If it is a flatter crown, such as the middle of a quarter panel or top of a roof/hood, it is more noticeable as the crown in these areas is normally minimal/just enough to maintain the shape, and may result in oil canning. If it is a concave crown, such as a reverse where the wheel opening flare comes outward, then the weld seam has a tendency to pull outward as it shrinks. The following pictorial shows an exaggerated crown and gap primarily so you can see it in such a small area. But it shows what happens as weld shrinkage and panel movement pull at the surrounding area. In the bottom view, the red line depicts where the crown was originally.

With tight butt welds we do need to planish in order to remove any deformation caused by shrinking, and add some stretch back into the area. This should be the extent of our planishing effort, as the tightly fitting panels prevent the panel pull from adjacent areas (that a gap allows, resulting in loss of crown). In the case of any gappage around a patch, we would need to planish even more to add enough stretch to overcome this loss of crown, or add filler as needed.


Looking at the quarter panel in the video, and welding that took place, one would expect in the case of a normal butt weld that the edges of the panels against each other will be a positive stop against any pull from adjacent areas. The only planishing we should need to do is to overcome any shrinking issues due to weld heat. While the theory looks good on paper, the angle cut did indeed close up the gap when compared to a straight cut. But it did not totally eliminate it. My concern with this type cut is that two angled surfaces do not provide the positive "stop" that a truly butted panel does in preventing panel pull from adjacent area. After the grinding process is done, checking the weld seam with a 6" ruler may show how flat that single weld is, but our main concern should be the crown across the entire patch to see if it has pulled inward causing a loss of crown. A defect such as that will be a pain to correct, filler or otherwise. I'm not intimately familiar enough with the method to say this will indeed be a concern. But these thoughts are more cautionary, to give you things to be aware of, to look for.. if you do give this method a try.. For the quarter panel, I would expect any shrinking/panel pull to cause the following issues to the crown:

…..and to a lesser extent, the slight crown from front to back, as the weld shrinks, will pull slightly inward. Armed with this theory on shrinking and panel pull, these are merely things to look out for. More planishing perhaps may be needed to remove any defects that might show up.

Thanks for the reply, Robert. Always good to hear from someone who knows what they're doing. Another reason I love this forum.... so much to learn.

 

[Yossarian]

Some casual observations... I would not recommend any novice use a 24 or 36 grit sanding disc on a 7" disc grinder for removing welds. Too much heat generated, can't see where you're sanding, a recipe for disaster when someone sands half the panel thickness away, or worse yet, sands through. Next, if you need to reweld after grinding, turn up the heat, you are not getting a full penetration weld. And now you need to grind again.

Part of the reason we use butt welds is to duplicate the original metal "flavor and feel" so that when someone looks in the trunk or under the floor pans, they don't see a flange repair, or have to contend with ghost lines on exterior painted panels. We can effectively cut out damaged (rusty) metal, butt weld in a new section, planish/metal finish/filler as needed, and we can have an invisible repair that for all practical purposes should be a permanent repair. The patch is normally already shaped to match (in the case of repops) so that the crown of the patch matches the existing panel. (NORMALLY) Part of the reason you see recommendation to use TIGHT butt welds, is that it eliminates open area that allows any panel movement, ie: as the weld shrinks, the panel pulls together. If the crown of our patch used to match prior to welding, weld shrinking along with the panel's pulling closer together (due to the gap) is going to pull in some of the crown. If it is a flatter crown, such as the middle of a quarter panel or top of a roof/hood, it is more noticeable as the crown in these areas is normally minimal/just enough to maintain the shape, and may result in oil canning. If it is a concave crown, such as a reverse where the wheel opening flare comes outward, then the weld seam has a tendency to pull outward as it shrinks. The following pictorial shows an exaggerated crown and gap primarily so you can see it in such a small area. But it shows what happens as weld shrinkage and panel movement pull at the surrounding area. In the bottom view, the red line depicts where the crown was originally.

With tight butt welds we do need to planish in order to remove any deformation caused by shrinking, and add some stretch back into the area. This should be the extent of our planishing effort, as the tightly fitting panels prevent the panel pull from adjacent areas (that a gap allows, resulting in loss of crown). In the case of any gappage around a patch, we would need to planish even more to add enough stretch to overcome this loss of crown, or add filler as needed.


Looking at the quarter panel in the video, and welding that took place, one would expect in the case of a normal butt weld that the edges of the panels against each other will be a positive stop against any pull from adjacent areas. The only planishing we should need to do is to overcome any shrinking issues due to weld heat. While the theory looks good on paper, the angle cut did indeed close up the gap when compared to a straight cut. But it did not totally eliminate it. My concern with this type cut is that two angled surfaces do not provide the positive "stop" that a truly butted panel does in preventing panel pull from adjacent area. After the grinding process is done, checking the weld seam with a 6" ruler may show how flat that single weld is, but our main concern should be the crown across the entire patch to see if it has pulled inward causing a loss of crown. A defect such as that will be a pain to correct, filler or otherwise. I'm not intimately familiar enough with the method to say this will indeed be a concern. But these thoughts are more cautionary, to give you things to be aware of, to look for.. if you do give this method a try.. For the quarter panel, I would expect any shrinking/panel pull to cause the following issues to the crown:

…..and to a lesser extent, the slight crown from front to back, as the weld shrinks, will pull slightly inward. Armed with this theory on shrinking and panel pull, these are merely things to look out for. More planishing perhaps may be needed to remove any defects that might show up.

Robert, the main point I took from the youtube vid was that it looked like a good way to get a well fitted patch if you were making your own, especially when dealing with irregular shape. I really appreciate your comments, lots of issues I had not considered.

 

[MP&C]

For a round shape like that, I would normally cut that out round to have the same distance of metal to the inside all the way around the seam. Given the "step" that the door sits in adds some strength, I would come outside that detail about 1" or so all the way around, just enough to planish the seam.

I think the main reason for using the method shown on the video is for him it takes any guesswork out of cutting a patch panel. It should fit doing it that way, and it did make the gap tighter, although still a gap. Welds will shrink, regardless of the method.. Just wanted to put out a bit more info in case someone did want to try that method.

 

[Yossarian]

For a round shape like that, I would normally cut that out round to have the same distance of metal to the inside all the way around the seam. Given the "step" that the door sits in adds some strength, I would come outside that detail about 1" or so all the way around, just enough to planish the seam.

I think the main reason for using the method shown on the video is for him it takes any guesswork out of cutting a patch panel. It should fit doing it that way, and it did make the gap tighter, although still a gap. Welds will shrink, regardless of the method.. Just wanted to put out a bit more info in case someone did want to try that method.

Good point.. thanks again.

 

['68 Coronet R/T]

Not trying to hijack the thread but since this is the go to for metal working I thought I would post my frustrations.

90% of the door is to a point that I am pleased with but one area is giving me fits.
Started with this and raised the low spots from the front of the door to the rear.

Things were progressing well until I got to this spot.
I have worked hours and hours on it, trying to be patient while raising the lows and lowering the highs.

The next picture is where I am at now after way too many hours. I am totally frustrated and ready to grab the filler.

Here it is from another angle where the lows and highs seem obvious but I have worked this over and over to the point where I am worried I will damage the metal if I keep going.

You can see some hammer marks in the one area. That is when I quit and decided to post the pictures.
I have been using a straight edge that I slowly drag from the top of the door toward the bottom to gauge my progress. Had it very close but that one area refuses to cooperate and now it looks worse that before I started working on it today.

Any suggestions would be appreciated even if it's "grab the filler." Honestly, I would much rather win this battle with the metal.

 

[MP&C]

I tend to go past the exit ramp at 90 mph, so I like slow, methodical processes that allow me to sneak up on something. For shrinking I like the donut dolly. I've used the shrinking tip on the dent puller, but unless you have a very pronounced peak, it doesn't work as well. ie: on a low crown with a slight bulge, the pinpoint shrink will tend to pull inward, leaving a dimple. The donut dolly I've had better luck keeping flat things flat (low crown).

If you don't have a donut dolly, try using a 3/4 drive socket with a smooth radiused opening that's about 1/4-1/2" diameter larger than the face of your hammer. A crowned hammer like the SO BF618 will tend to work more effectively, but too much swing and this will leave dimples. You want to push a slight amount of metal into the dolly where after "springback" it is now flat. A flat (low crown) hammer will take a bit longer, but again, you don't miss the exit ramp. Here's a simulation of the donut dolly...

It basically gives you off dolly on steroids, as the off dolly "support" is on more than one side. For me, I'd try this in bringing down some of those highs and gathering up the excess metal..

 

['68 Coronet R/T]

Thanks, I will give this a try.
I have a shrinking disc and that seemed to be helping until I needed to smooth out the surface to match the surrounding metal. I would put the straight edge on and as I dragged it toward me watching for gaps there would be maybe 1/32" of space in places but clearly points where the straight edge will teeter-totter ever so slightly.

Lately it seems like I am making that small bad spot into a larger and larger mess.

 

[MP&C]

The nice part about the "official" donut dolly is it's made of UHMV, which is more forgiving of less accurate strikes, not as likely to stretch. With using a socket, if you strike the edge you'll get the on-dolly ping and know that you missed. So perhaps use this with extremely light taps as a locating method and then strike when you've found the center. If a larger socket helps.... use what you must.

 

[Chris_Hamilton]

Another way to go about it, being that you have a shrinking disc (I think I recall you saying you did), if you don't you can use the backside of a large grinding disc. Not the face, but the phenolic backside, in the area where you have highs (smaller section closer to the door handle) hammer on dolly until the whole are is a smooth low swell. Then run the shrinking disc over that area and quench. Lube the (metal) disc with some WD or wax. If you are using a grinding disc no lube is necessary. In the persistently low areas, again use a dolly from the backside and bump up firmly with the dolly. Then start on the perimeter and work either clockwise or counter clockwise in a spiral toward the center, with the hammer and dolly. When you are hammerring on dolly keep a lot of upward pressure on the dolly. Keep bumping and then hammering on or off dolly (depending on what's needed). As you get close this is where a slapper file come in handy. You should be able to bump the low area up pretty close, then use hammer, dolly, and slapper to work everything even.

Personally I have a couple of those shrinking discs but I like using the backside of old 7" grinding discs because they don't mar the metal like a metal shrinking disc will. If you go the shrinking disc route, go easy and sneak up on it. Remeber too that it will take a combination of hammer on dolly, hammer off dolly, and bumping. Up to you to determine what is needed where.

 

[sprint_9]

I don't remember if you told me this MP&C, at one point I talked to you or read one of your posts on the donut dolly.

Anyway, when i worked on my hood I used a PVC fitting for the dolly. I used a tee just to have a little more to hold on too but it did work alright. My problem was stopping too soon and not continuing to work it. Might be a more forgiving option over a socket.

Another thing that helped was making a grid to try and stay lined up, or at least attempt to.

 

['68 Coronet R/T]

Another way to go about it, being that you have a shrinking disc (I think I recall you saying you did), if you don't you can use the backside of a large grinding disc. Not the face, but the phenolic backside, in the area where you have highs (smaller section closer to the door handle) hammer on dolly until the whole are is a smooth low swell. Then run the shrinking disc over that area and quench. Lube the (metal) disc with some WD or wax. If you are using a grinding disc no lube is necessary. In the persistently low areas, again use a dolly from the backside and bump up firmly with the dolly. Then start on the perimeter and work either clockwise or counter clockwise in a spiral toward the center, with the hammer and dolly. When you are hammerring on dolly keep a lot of upward pressure on the dolly. Keep bumping and then hammering on or off dolly (depending on what's needed). As you get close this is where a slapper file come in handy. You should be able to bump the low area up pretty close, then use hammer, dolly, and slapper to work everything even.

Personally I have a couple of those shrinking discs but I like using the backside of old 7" grinding discs because they don't mar the metal like a metal shrinking disc will. If you go the shrinking disc route, go easy and sneak up on it. Remeber too that it will take a combination of hammer on dolly, hammer off dolly, and bumping. Up to you to determine what is needed where.

When you say "bumping" are your referring to hitting upward with the dolly?

 

[Chris_Hamilton]

When you say "bumping" are your referring to hitting upward with the dolly?

Yes, getting behind the panel on the backside with a dolly that has a similar profile to the shape you are working on, and hitting it up. Using the dolly like a hammer of sorts to push the panel up. That is bumping. Try to bump up the lows as much as you can then smooth(planish) with the hammer and dolly or slapper and dolly. You may have to repeat several times and spot shrink areas as you are doing this. Shouldn't have to do a lot of stretching, just bumping up, planishing off, bumping up some more until you get it to where you are satisfied.
Re-read those 2 Jeff Lilly links I posted in your thread.

 

[JimKueneman]

Trust me filler can give you fits and way to many hours too

 

['68 Coronet R/T]

Yes, getting behind the panel on the backside with a dolly that has a similar profile to the shape you are working on, and hitting it up. Using the dolly like a hammer of sorts to push the panel up. That is bumping. Try to bump up the lows as much as you can then smooth(planish) with the hammer and dolly or slapper and dolly. You may have to repeat several times and spot shrink areas as you are doing this. Shouldn't have to do a lot of stretching, just bumping up, planishing off, bumping up some more until you get it to where you are satisfied.
Re-read those 2 Jeff Lilly links I posted in your thread.

I did read those again. When I get a chance I will try both the doughnut dolly and the bump and planish.
My slapper is smooth and not the file type.
I'll have to look into getting more tools.

 

[MP&C]

A donut dolly test sample:


One of the guys over on the metal shaping web sites, Daniel Gunderson, sells the "official" donut dolly. Compared to the typical off-dolly bumping, it works more proficiently in off-dolly shrinking a crowned panel because it supports the bottom side in more than one spot (around the perimeter) as the panel is bumped from the top in the center of the donut dolly. This would seem to be useful in body repair, especially to address high spots found after blocking primer where heat would not be as feasible.

Some time ago, someone on another forum asked for advice in removing an outward roof dent, a result of some over-eager on-dolly stretching in removing dents... I suggested a low-buck alternative to the donut dolly, simply using a PVC pipe fitting. Where it may not work as aggressively as the donut dolly which has more mass, sometimes slower is better, especially when trying something new. Trying this process for myself in the shop, and rather than use the roof of something sitting here, we will use a piece of 18 ga CRS to simulate a roof.

Grid layout for the Wheeling Machine, and completed "sample" roof...

The first order of business should be to make some profile templates. In the case of an actual dented roof, use the opposite, undamaged side. This will allow you to check your progress as you go, and easily find the remaining high spots.

Using a crowned body hammer, a "dent" will be added from the back side, crossing both directions where the templates were taken.

With the dent added:

I chose to use a PVC elbow, a "tool" readily available and economical. As with any body tool, they should be free of any burrs that may mar the metal surface, so I sanded a slight radius into the edges...

Holding the dolly against the bottom of the panel, you can see that due to the dents it only touches the panel at the red arrows. Based on off-dolly principle, the shrink would occur more prominently in the direction of the red arrows, which is exactly where the stretch lies.

Here are the tools we will use today:

After some off-dolly bumping:

Check with the templates

Progress....these are light taps only with the hammer. We just want to bring down the high spots, not create craters.

Here's where I finished up...

I have a little over an hour in making the panel, denting, and removing the dent. Where I still could have gone a bit more, it was about to a point where high build primer should have masked any remaining imperfections. This dent removal could also have been accomplished with heat shrinking using an O/A torch, etc, but for those times where you may not wish to use heat (primer is already sprayed) and want another option, this seems to work well.

 

[JimKueneman]

A donut dolly test sample:


One of the guys over on the metal shaping web sites, Daniel Gunderson, sells the "official" donut dolly. Compared to the typical off-dolly bumping, it works more proficiently in off-dolly shrinking a crowned panel because it supports the bottom side in more than one spot (around the perimeter) as the panel is bumped from the top in the center of the donut dolly. This would seem to be useful in body repair, especially to address high spots found after blocking primer where heat would not be as feasible.

Some time ago, someone on another forum asked for advice in removing an outward roof dent, a result of some over-eager on-dolly stretching in removing dents... I suggested a low-buck alternative to the donut dolly, simply using a PVC pipe fitting. Where it may not work as aggressively as the donut dolly which has more mass, sometimes slower is better, especially when trying something new. Trying this process for myself in the shop, and rather than use the roof of something sitting here, we will use a piece of 18 ga CRS to simulate a roof.

Grid layout for the Wheeling Machine, and completed "sample" roof...

The first order of business should be to make some profile templates. In the case of an actual dented roof, use the opposite, undamaged side. This will allow you to check your progress as you go, and easily find the remaining high spots.

Using a crowned body hammer, a "dent" will be added from the back side, crossing both directions where the templates were taken.

With the dent added:

I chose to use a PVC elbow, a "tool" readily available and economical. As with any body tool, they should be free of any burrs that may mar the metal surface, so I sanded a slight radius into the edges...

Holding the dolly against the bottom of the panel, you can see that due to the dents it only touches the panel at the red arrows. Based on off-dolly principle, the shrink would occur more prominently in the direction of the red arrows, which is exactly where the stretch lies.

Here are the tools we will use today:

After some off-dolly bumping:

Check with the templates

Progress....these are light taps only with the hammer. We just want to bring down the high spots, not create craters.

Here's where I finished up...

I have a little over an hour in making the panel, denting, and removing the dent. Where I still could have gone a bit more, it was about to a point where high build primer should have masked any remaining imperfections. This dent removal could also have been accomplished with heat shrinking using an O/A torch, etc, but for those times where you may not wish to use heat (primer is already sprayed) and want another option, this seems to work well.

Versatile plumbing parts. I’ll have to get my plastic street 90 Mopar upper balljoint rubber sleeve driver out and show it off!