Correct way to remove a section of frame? knowlege needed!

[supersize75k5]

I hope this fits in the COG rules /forums/images/graemlins/thinking.gif

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1) Is this *directly* fab related?
2) Does it go beyond the common or basic?
3) Is it true to say this is not available "off the shelf"?

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/forums/images/graemlins/dunno.gif


On my 72, I am removing 14.5 inches from the frame, right behind the cab. This is the spot most trucks I have seen converted to a shortbed are doing it.

But I want to do it right, so please help or point me to some info so I dont take my life in my hands /forums/images/graemlins/waytogo.gif

I was also needing to know if the "diamond" or "fish mouth" plates are the right way to do it. I also need to know if I plate both sides of the frame rail, or just one side?

How thick of plate? 1/4?

Thanks you so much for any help you can give!

 

[cybrfire]

I think the fish plates should be shaped like <> that. I'd try to get that shape bent into a channel though so it would also grab the top and bottom lips of the c channel. Beyond that I'd also Bolt it on and then weld it. Say 3 bolts on each side of the cut.



Cut frame.
Pull together and weld.
Put on fish plate channels and bolt.
Weld plate edges in a skip pattern.

That's just how I would do it if I had to.

OH, I think 1/4" should be dandy and I don't think both sides would be necessary.

 

[Resurrection_Joe]

My buddy desert rat just moved the springs forward and cut off the rear of the frame, a bit simpler structurally, but it'll take some extra fabbind to get everything to sit right

 

[ntsqd]

Be sure to 'V' the edges at least 1/3 deep on each side. After butt welding the rails grind the sides + top & bottom smooth.

Cut the suggested diamond shaped side plates from steel roughly the same thickness as the frame itself. Maybe cut them from the piece removed? I think one per rail is enough. If you opt for one on each side of each rail do NOT make them the same size, offset the sizes enough that the welds are as far apart as you can get them. I would also round the corners rather than leave them sharp. Pull your weld bead all the way up to the top corner of the plates. The idea is to make the change in rail cross section as gentle as possible.

Then I would run a length of strap down the outside of the flanges. Again, the thickness doesn't need to be any thicker than the rail thickness. The bottom strap will be mostly in tension so make it longer than the top strap. Bring the ends of the straps to a point, don't cut them square. If you do cut them square, don't weld the ends. I would skip-weld the straps rather than seam them.

You might also consider some Rosette holes in the plates and the straps.