Advice on Flattening+ Filling Accessory Holes

More of an art than a science - discuss metalworking and welding here.

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Joined: Wed Sep 16, 2020 10:46 am

PostPosted: Wed Sep 16, 2020 10:49 am
Hello! First post here, forgive any naivety.

I recently purchased a former municipal vehicle that had a light bar on it's roof. I was able to remove the light bar, but am left with holes and some bent body metal. The holes are about 3/4 in wide and, unfortunately, impossible to access from behind.



I'm looking for advice on two areas:

1. Flattening the metal around the hole. Currently, it's a bit flared up due to how the accessory light was attached. Presumably, before filling the hole, this metal should be flattened, or even bent inwards to allow filler to create a flush surface.

2. Filling the holes. Was thinking that I would do this with bondo, but haven't really gotten that far yet.

Thanks in advance!!

Oh also -- the strange color in the photos is due to the current smoke situation in Portland Oregon...

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PostPosted: Wed Sep 16, 2020 4:57 pm
If you just use filler to fill those holes the filler will crack and fail. They are far too big to fill without support from behind.

So, bad news is that you'll have to drop the roof lining and then hammer and dolly until all that bent metal is straight. Ideally, weld a patch behind and then skim a little filler to finish off. Alternately, there are high strength panel adhesives that I've used in similar situations with great success since there is no heat from welding to warp the rest of the panel, nor any welds to grind off.

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PostPosted: Thu Sep 17, 2020 7:08 am
IMHO, there's 2 ways to go, the 'right way', and the easy way. The right way will last as long as the car, the easy way, if you get a year or 2, that's normal. Might last forever, might crack after that.
The "right way": weld a patch in, as NFT5 said. On a ragged hole like that, I'd use a Unibit, and hog the hole out to around 1". Removes a lot of the wrinkled area, and makes it uniform for a new patch to make. You WILL have to remove the headliner to do some hammer and dolly work, and coat the repair on the inside with a rust preventer.
The "easy way": Unibit the hole out until the area is smooth (or use snips, since it's a larger area). Make a metal patch about 1/4" larger all around, a bit of JB weld around the edges , use a strong magnet (or tack weld a piece of rod to it), and insert it into the hole and pull up to glue to the inner surface. Next day, light grind, spread more JB over the area to seal it, and when dry, use some body filler to finish.
I hate to do down and dirty work like this, but on a car that's not worth doing a ton of work on, it makes it presentable.

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