More welding quesitons - how much overlap?

[tdskip]

So two questions;

1)How much of an overlap should I plan on, or should I be trying to butt-weld everything?

2) Do you use weld through primer? Necessary to prevent rusting?

Here is the area in question. Remaining metal is in better than it looks, and will be well cleaned and prepared prior to any welding.

Thanks!

 

[dklawson]

Others will offer their own opinions, but when I am working with patch panels that won't be seen I overlap by about 1/2". I stitch the patches in place making welds about 1" long, allow the area to cool, then weld 1" somewhere else. Eventually it all gets stitched together with minimal warping. I save butt welding for areas that are visible but hard to grind smooth.

If a patch is in a location that is hard to protect later with paint, I use the weld-thru primer. (i.e. On non-Triumph projects... places like inside the sills/rockers). If the welded area can be accessed easily after the repairs are done I don't bother with the weld-thru primers as they are expensive.

 

[StupidHippie]

Hi,

Looks like a nice straightforward repair, I'd butt weld in a heartbeat. Take the time to fit the patch properly and it will be gorgeous.

Here's a similar repair I did to my '74:
before...

after...

No need for primer until the patch is done. Clean it really well then clean it again and prime.

Hope this helps,
Rob

 

[foxtrapper]

Overlaps trap water and rust up nicely as a result. You can take measures to reduce this, but it's an inherent aspect of an overlap.

Butt welds are much more demanding of your welding skills and metal cutting, but do not trap water.

 

[dklawson]

You are of course correct that overlaps can trap water. I should have mentioned that once I have done a repair with overlaps I paint the panel and the joint. I apply seam sealer over the repairs when the paint is dry.

 

[TR6oldtimer]

All the panel joints on the older cars are lap joints.

 

[IanF]

All the panel joints on the older cars are lap joints.

Given the tendancy for older car to rust, that's not exactly a glowing endorsement.

 

[swift6]

All the panel joints on the older cars are lap joints.

Given the tendancy for older car to rust, that's not exactly a glowing endorsement.

Had more to do with poor rust protection of the metal than lap joints though. Lap joints properly protected with sealing compound and paint, on cars that no longer see nearly as rough miles or harsh elements that they did while they were younger, will likely last until we no longer use refined crude as a power source. After that it might not matter.

 

[tosoutherncars]

As above; either should be fine, as long as you clean thoroughly, use weld-through primer on any lap welds, and paint / seam seal soon after welding.

- If you do flange it, your local Princess Auto / Harbor Freight type place should have cheap flanging pliers. They make the job a lot easier and cleaner-looking.

- The tightness of the patch against the original metal is VERY important, to prevent burn-through and ensure good adhesion / weld strength. If you flange it, I would suggest putting a sheet metal screw or two through each side of the patch (both pieces) to hold everything tight until you get the first few tack welds down. The screw holes are easily filled once you're done; low power, med-high wire speed.

- You may want to add a few sides to your hole / patch, even if it seems to make the shape more complex. Cutting, flanging and welding skinny, acute-angled points (without blowing through) is much more difficult than dealing with 90 deg. angles. I would suggest something more like the following (rotten ASCI art follows.)

...____....................
..|......|...................
..|......|...................
..|......|_________....
..|........................|...
..|........................|...
..|.............._____|...
..|............./..............
..|.........../...............
..|........./................
..|........|.................
..|........|.................
..|........|.................
..|____|.................
............................

 

[billspit]

I did very narrow flanges on my pieces. I wasn't good enough to butt weld much stuff. Too much burn through.

I also could not weld through the weld through primer. I used it except exactly where I would be welding.