[jrock]

I have some rot that I'm making a patch for from a quarter skin. Here's what I have.

Here's two shapes I could do. Is one really superior over the other? This will be butt welded.

Follow along the shape of the rot?

Or this rectangular shape? I hate to take out excess good metal if I don't need to but maybe there's an advantage cutting it like this???

 

[Woodchuck]

Not particularly, but for $32 it's a lot handier to simply cut up a patch panel Frankly, I'd cut as little as possible to get to "good" metal.

https://www.summitracing.com/parts/shi-465-60l?seid=srese1&gclid=CjwKCAiAuOieBhAIEiwAgjCvckjKFLzVLsx4IikW1u4YGT9WhPSfYDNGi0AAmmdH1LbbBRmBSEmCzxoCQuQQAvD_BwE

 

[jrock]

I was thinking the rectangular due to making the patch easier to fit instead of all the curving. But we'll see what happens.

 

[JohnnyK]

Does not matter, in my opinion. When I redid my car, entire quarter panels weren't available (or easily available, to my knowledge) for a 67 fastback, so you had to make do and get creative. Same idea. Just know some shapes may make the weld area bend in strange ways when it shrinks.

 

[2+2=GT350]

1st pic...then trace paper/cardboard to fit ...place template on donor/repair piece...cut/remove... spot weld in then stitchweld in place ...not losing any stampings there.

 

[jrock]

1st pic...then trace paper/cardboard to fit ...place template on donor/repair piece...cut/remove... spot weld in then stitchweld in place ...not losing any stampings there.

I'm glad that it is in a spot where there's no deeper contoured body lines like you said.

 

[Nailbender]

Every time I have tried to do the minimum patch I was punching holes through everywhere with the mig welder because of the thin metal. I would buy the patch panel and go a minimum of 1 1/2" above the highest pin hole. Cut everything out including drilling the spot welds out on the lower flange. You will never see a restoration shop doing a minimum repair like you propose because there's no way to guarantee it, you have to make sure you've got above all the rust even the rust in the doubled up metal you can't see. Use butt welding clamps on the seam with plenty of patience. Good luck!
16pcs Butt Welding Clamps Sheet Metal Auto Car Door Skin Panel Fender Kit | eBay

 

[vegasloki]

Here’s how I would do it and why. It’s the same way the big dog shops do it.

Buy a complete lower patch panel.

QUARTER REPAIR PANEL, LOWER REAR, LH - #200-1LH - National Parts Depot

Buy part #200-1LH QUARTER REPAIR PANEL, LOWER REAR, LH for your classic 1967-1968 Mustang from National Parts Depot. Free shipping on orders over $300, fast delivery & everyday low pricing! Order now!

www.npdlink.com

Strip all the paint/coating about 2’ up from the bottom of the panel and see where the rust ends.

Take the patch panel and cut a straight horizontal line at the point measured on the car.

Take machinist blue and paint the rotted panel at the place where the rust ends.

Fit the replacement panel. Using the cut edge on that panel scribe a line on the car through the machinist blue. A regular Sharpie is too thick. Cut the rotted panel at that line.

You can join the two while you tack it with a variety of methods. Your choice. I use either Cleecos or copper backing clamps.

The they do it like this as it reduces the heat input into the panel because the straight line weld is shorter. When you weld on a poly curve patch like you’ve shown you’re putting more heat into it and the welds are closer together which further promotes distortion. Using a straight line it’s easier and more precise than trying to cut and fit a compound curve.

By using a stamped replacement panel you keep the contour lines in the area where you’ve replaced metal. Otherwise you need to shape a contour into the patch with some sort of shaping, English wheel, hammer/dolly whatever.

When your done welding flap sand the bead smooth on both sides, epoxy prime, mud, block and paint.

 

[SLO65351]

Jrock I tried doing the small patch on my quarter but the metal was so worked over from previous work/damage it would not conform to my methods so I cut all of it out and started fresh.(take a look at my build thread I have some good pics)

 

[xcelr8]

Buy a cheap quarter panel, over cut off what you need and graft it in properly.

 

[Mustangerbob1]

IMHO, this is very wrong. I have fixed a stack of these, and the amount of work you are contemplating is WAY out of proportion to any savings.

Buy the "short panel, scribe it, and cut it in.

With the rust you have, you have thin metal, and it may burn out.

Save the grief, and use a conventional repair panel, Straight lines, etc.

 

[Lizer]

Here’s how I would do it and why. It’s the same way the big dog shops do it.

Buy a complete lower patch panel.

QUARTER REPAIR PANEL, LOWER REAR, LH - #200-1LH - National Parts Depot

Buy part #200-1LH QUARTER REPAIR PANEL, LOWER REAR, LH for your classic 1967-1968 Mustang from National Parts Depot. Free shipping on orders over $300, fast delivery & everyday low pricing! Order now!

www.npdlink.com

Strip all the paint/coating about 2’ up from the bottom of the panel and see where the rust ends.

Take the patch panel and cut a straight horizontal line at the point measured on the car.

Take machinist blue and paint the rotted panel at the place where the rust ends.

Fit the replacement panel. Using the cut edge on that panel scribe a line on the car through the machinist blue. A regular Sharpie is too thick. Cut the rotted panel at that line.

You can join the two while you tack it with a variety of methods. Your choice. I use either Cleecos or copper backing clamps.

The they do it like this as it reduces the heat input into the panel because the straight line weld is shorter. When you weld on a poly curve patch like you’ve shown you’re putting more heat into it and the welds are closer together which further promotes distortion. Using a straight line it’s easier and more precise than trying to cut and fit a compound curve.

By using a stamped replacement panel you keep the contour lines in the area where you’ve replaced metal. Otherwise you need to shape a contour into the patch with some sort of shaping, English wheel, hammer/dolly whatever.

When your done welding flap sand the bead smooth on both sides, epoxy prime, mud, block and paint.

There's a slightly easier and more precise method for this instead of using the machinist blue, which I've never used and don't own.

Remove all of the old panel except anything that will be overlapping about 1" with where you intend for the patch to go. Lay the patch piece on and clamp into place on the pinch welds, and use a few self tapping metal screw to screw the patch to the original metal it's overlapping by about an inch.

For the next part the very edges of the patch panel will get cut off too. Cut through both the patch panel (near its edge) and the original panel with a 3" cutoff wheel, with the cutting wheel going through the metal at an ANGLE and not perpendicular to it. When the cut is made at an angle through the metal it makes for a smaller gap. Doing it this way makes the exact same cut in both the patch and the original metal. If you jump or veer a little bit on your line, it does it with both pieces so it's an exact fit.

The part linked here looks like a pretty ****ty part, btw, according to NPD's warning in the description.

 

[jrock]

Wow. Thanks everyone for the opinions/options. I will look over these again tomorrow and see what I'm going to end up doing. I was thinking of just a cut out and patch but have many options to think about and choose on now. Much appreciated!

 

[vegasloki]

There's a slightly easier and more precise method for this instead of using the machinist blue, which I've never used and don't own.

Remove all of the old panel except anything that will be overlapping about 1" with where you intend for the patch to go. Lay the patch piece on and clamp into place on the pinch welds, and use a few self tapping metal screw to screw the patch to the original metal it's overlapping by about an inch.

For the next part the very edges of the patch panel will get cut off too. Cut through both the patch panel (near its edge) and the original panel with a 3" cutoff wheel, with the cutting wheel going through the metal at an ANGLE and not perpendicular to it. When the cut is made at an angle through the metal it makes for a smaller gap. Doing it this way makes the exact same cut in both the patch and the original metal. If you jump or veer a little bit on your line, it does it with both pieces so it's an exact fit.

The part linked here looks like a pretty ****ty part, btw, according to NPD's warning in the description.

That’s a good cutting technique. I’ve seen the tech screw method though I use Cleecos. Blue is common for this kind of fab, it's handy to have in many situations. The Cleecos and blue I first used when I built race cars. Though I’ve resisted attaching the Mustang panels with Dzus fasteners… 🤣

 

[Lizer]

That’s a good cutting technique. I’ve seen the tech screw method though I use Cleecos. Blue is common for this kind of fab, it's handy to have in many situations. The Cleecos and blue I first used when I built race cars. Though I’ve resisted attaching the Mustang panels with Dzus fasteners… 🤣

What size hole do the clecos use? I've really considered switching over to them.

 

[vegasloki]

What size hole do the clecos use? I've really considered switching over to them.

Mine are 1/8” but they also make 3/16”.

 

[MSMach1]

What size hole do the clecos use? I've really considered switching over to them.

Clecos are sized for number hole sizes: #40,30,21 and 11 which roughly correspond to rivet sizes of 1/16”, 1/8”, 5/32” and 3/16”.
Clecos are mostly used in aviation because the holes are filled with rivets or screws and panels can be removed easily and sealed without deforming the holes, but I just use the sheet metal screws for steel panels. They are cheap.
I have found the sheet metal screws pull much tighter, are much smaller and you don’t run the risk of the heat taking the temper out of the Cleco springs. The holes will get welded up anyway, so deformation is not an issue.
IMO, I wouldn’t retool just to get Clecos

 

[Lizer]

Clecos are sized for number hole sizes: #40,30,21 and 11 which roughly correspond to rivet sizes of 1/16”, 1/8”, 5/32” and 3/16”.
Clecos are mostly used in aviation because the holes are filled with rivets or screws and panels can be removed easily and sealed without deforming the holes, but I just use the sheet metal screws for steel panels. They are cheap.
I have found the sheet metal screws pull much tighter, are much smaller and you don’t run the risk of the heat taking the temper out of the Cleco springs. The holes will get welded up anyway, so deformation is not an issue.
IMO, I wouldn’t retool just to get Clecos

Excellent. I'll save my money then because those Cleco's and the tool used for them are not cheap. In my body classes we always used sheet metal screws.

 

[DonP]

The patch is not shaped the same as the original sheet metal. It lacks the recesses on the underside and behind the rear valance. If you can, I'd try to maintain the orginal recesses. I don't even know how the rear valance would attach without the recessed area to the rear.

 

[jrock]

The patch is not shaped the same as the original sheet metal. It lacks the recesses on the underside and behind the rear valance. If you can, I'd try to maintain the orginal recesses. I don't even know how the rear valance would attach without the recessed area to the rear.

I've pretty much convinced myself to just cut out a rectangular area around the rust and not get into the body lines etc. I stripped the car to bare metal before it was primed and can confirm the rust is just in that area but I'll cut to make sure I'm into good metal. And like you mentioned I'm concerned about the lines of the reproduction piece in certain areas. Lots of great ideas on here though I had to think about.