Frame Repair - Patch Options

I recently purchased a 2004 Chevrolet Colorado with the AR5 manual that I plan to LS swap. When I got the truck home, it was apparent that the frame was a total loss. I found another rolling frame locally that was advertised as being good and no issues. Getting the new frame home I did a thorough inspection and noticed some thin areas so I cut them out. 

Now I need to patch the holes. The frame is a fully boxed frame, 1/8" thick metal. I now have two patch areas on the inside of the frame, approximately 5"x 10". On the outside of the frame, there's some areas of this metal that I plan to add some large "cap" areas similar to the large patch areas in the photo below. 

The biggest question I have is what to do with the 5"x10" patch areas should I "cap" these areas with patches? When I say cap, I mean cutting the patch larger than the hole I cut and weld to the good surrounding metal? Line below:

Or should I butt weld the patch to the hole I cut and add fish plates over top? 

If it were me, I'd butt weld patches to fit the cut out areas and then add fish plating. It might be overkill but more material can't hurt. A lot of the integrity of these repairs depends on your welding skills more than the patch style chosen. Alternatively, is finding a rust free frame from the south an option?

Agreed.   Fit patches to the holes, butt weld them flush, and then you could plate over the top, of you'd like.   Avoid vertical cuts and welds in the frame as much as humanly possible.

Cap, because it's rustier than you think and butt welding will result in many blowthroughs.

You will probably find yourself making mini caps for various areas to overlap the cap.

In reply to Pete. (l33t FS) :

Spent the afternoon trimming my cap patches to butt weld. I'm going to weld them in, grind the welds smooth and completely overlap the butt patch (lol) with a cap. I figure this is the best option for getting the benefits of both patch types. 

Bumping this thread because I need a sanity check. Is this frame too far gone? These are the size of the cut areas I had to make to get rid of the rot. Trying to weld patches with my Titanium 125 flux core welder is going okay, but I am blowing throw in a couple of places.  Should I keep at this with the plan above? Or should I cut my losses and buy another truck?

I've done the same quantity, never on such a new frame though. Didn't realize those rusted so badly.

Patch area doesnt look too bad but patch welding looks a little suspect.  

I echo the welding statement.  But, a grinder and paint, make me the welder I aint...

I'm not too keen on the 90 degree corners, I would have drilled the corners then cut to them.  I'm sure if you get a full pen weld it wouldn't matter, but anything with sharp corners is a crack waiting to happen.  With the frame and patches being 0.125" thick, you could try giving one or both pieces a small bevel on the edges to get better weld penetration.  

I too am a little concerned with the repair welds. 
 

But first did you grind the area inside the frame rail down? It looks a little suspect, but could be the pic (highlight)  

In terms of patch, this area is making me nervous a lot of bends and it looks like this area got hot during welding. Check for warping? 
 

On the other side, these corners should be radiused and beveled. And I'd check this seam thoroughly it looks janky. I'd grab a chisel and sledge and hit it HARD a few times. Also magnet check the inside (magnets don't stick well to rust). 
 

I would want a better frame if I was going to go through all the trouble of a frame swap.

But those are also vertical cuts and vertical welds, in the location the frame will see most of its stress.  

Pickup truck frames flex and twist, a lot. Your MIG welds are harder than the parent metal.  With vertical cuts and welds, you end up with stress risers that are going to cause cracks in the frame.      A curved or tapered cut and weld works much better.

While this is a fissh plate, it will give you a better idea of what I am talking about-

But as I said, I would just find a better frame.   It all depends on how much work you are willing to do.






 

This is why I suggested cap   It makes for a stronger joining, even if there's a blowthrough here or there.

and yeah, if this is to swap IN?  Start with a better frame.  Patch welds are to get another year or three from a frame before you scrap the truck.

In reply to Pete. (l33t FS) :

Thanks. This is what I need to hear. If the consensus is this repair will only last a few years, it's just not worth it. 

And also, my welding up top isn't final. I got a decent weld on the top, but because the metal was thin on the sides, I had to do a lot of small tacks. I went back through and got some good welds over those areas. I was then going to add fish plate style caps over these patch areas.