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Discussion Starter #1
hello,
i have cut out the rust under the hood lid, and tomorrow will be welding the new patch in. when i do that should I weld a little piece along the edge to rest the patch on or is there a better way to do this. note: i cant access the back side of the patch. see picture

after i weld i will be applying bondo to clean it up
 

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I'm not a body expert, but I think I would have treated the surface rust inside, removed some of the rusted metal, and fiberglassed it in, so as to retain the original shape. Welding on hoods is very tricky, the metal is so thin, and it gets hot and warps easy, so do a lot of little tack welds and let it cool in between. I would make the box shape you need, and make it a little smaller than the opening, so you can do a lap weld. Good Luck.
 

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hello,
i have cut out the rust under the hood lid, and tomorrow will be welding the new patch in. when i do that should I weld a little piece along the edge to rest the patch on or is there a better way to do this. note: i cant access the back side of the patch. see picture

after i weld i will be applying bondo to clean it up
You kind of got a little ahead of yourself here so it will be a little more difficult, but you just butt weld the new piece in.

Normally, I would suggest to take a thin, flexible piece of cardboard such as a serial box and use this to make a template of your problem spot on the metal (before you cut ANYTHING away from the metal). You can keep trimming the cardboard down until it covers the entire area into good metal. Once you have your template made, trace around it with a sharpie or a scribe and make your cut.

Then take your cardboard template and trace it into your metal to be used for the patch and cut it out. Do a test fit of the patch over the new piece. You may have to do some slight fabrication to the patch such as giving it bends and contours to match the original, but this isn't overly hard. If you need to give a slight bend, tap the area needing bent against a pipe of the right or close diameter. Bends can be made by putting the piece in a vice, leaving however much you need in the bend sticking out, and then pounding it down flat so it's at a 90 degree angle to the rest of the piece (or whatever angle you need).

Most of metal working is just being very creative with what you have.

To hold the piece while you buttweld it in, I use a stud welder to attach a stud or two to the piece so I can hold the stud to hold the piece flush. If you don't have one of these, try tack welding a tiny thin metal tab to the center of the piece (or however many tabs you need) that you can use to hold the piece. Then cut them off and grind down when done.

Once your piece is in, begin making tack welds spaced out. Let them cool naturally (don't blow on them or put a cold rag on them) or else you will get excessive shrinkage. Do not make continuous welds, only tacks, or again the area gets too hot and you get excessive shrinkage. Finally, the area should be cool before you put another tack weld in that area. I feel with my fingers to make sure the area I want to put a tack has completely cooled.

To help, here's patch with a piece of metal I fabricated to fix a patch in the corner on the bottom of the door. I had some large gaps to fill in leaving this weld less than pretty.

1967 Mustang Restoration: door skin and repair, part 2


Here's a thread on a sail panel I replaced. All these repairs are butt welds.

http://www.allfordmustangs.com/forums/classic-tech/295727-replacing-b-pillar-sail-panel-demonstration.html
 

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Discussion Starter #4
You kind of got a little ahead of yourself here so it will be a little more difficult, but you just butt weld the new piece in.

Normally, I would suggest to take a thin, flexible piece of cardboard such as a serial box and use this to make a template of your problem spot on the metal (before you cut ANYTHING away from the metal). You can keep trimming the cardboard down until it covers the entire area into good metal. Once you have your template made, trace around it with a sharpie or a scribe and make your cut.

Then take your cardboard template and trace it into your metal to be used for the patch and cut it out. Do a test fit of the patch over the new piece. You may have to do some slight fabrication to the patch such as giving it bends and contours to match the original, but this isn't overly hard. If you need to give a slight bend, tap the area needing bent against a pipe of the right or close diameter. Bends can be made by putting the piece in a vice, leaving however much you need in the bend sticking out, and then pounding it down flat so it's at a 90 degree angle to the rest of the piece (or whatever angle you need).

Most of metal working is just being very creative with what you have.

To hold the piece while you buttweld it in, I use a stud welder to attach a stud or two to the piece so I can hold the stud to hold the piece flush. If you don't have one of these, try tack welding a tiny thin metal tab to the center of the piece (or however many tabs you need) that you can use to hold the piece. Then cut them off and grind down when done.

Once your piece is in, begin making tack welds spaced out. Let them cool naturally (don't blow on them or put a cold rag on them) or else you will get excessive shrinkage. Do not make continuous welds, only tacks, or again the area gets too hot and you get excessive shrinkage. Finally, the area should be cool before you put another tack weld in that area. I feel with my fingers to make sure the area I want to put a tack has completely cooled.

To help, here's patch with a piece of metal I fabricated to fix a patch in the corner on the bottom of the door. I had some large gaps to fill in leaving this weld less than pretty.

1967 Mustang Restoration: door skin and repair, part 2


Here's a thread on a sail panel I replaced. All these repairs are butt welds.

http://www.allfordmustangs.com/forums/classic-tech/295727-replacing-b-pillar-sail-panel-demonstration.html

yeah your right, i just got so excited that i finally got my hands on cutting tools that i was able to tackle this project that has been hanging over my head (and i wanted to try out my new mig) but i will remember those directions for the next time as i have a few more spots to do.
 

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It's not a necessity, it only makes the project easier. You still may be able to get a piece of cardboard under there and trace around the opening to get a pattern. All you have to do is get creative. The rest still applies.
 
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