Any fabricators willing to give me some insight? I’m a competent welder and have built a couple frames over the years for hot rods, but it’s time to stretch out my crewcab for a longbed and I’m wondering if my idea of notching the frame would work. I have some 4”x4”x 3/16 tube and am trying to figure out how to weld it to the weird x frame portion where it measures to 4 inches wide and 4 inches tall. Will cutting the red part of the frame and notching the new tube to match be strong enough after adding fish plates? I plan on towing my camping trailer and using the truck for dump runs and such and want to make sure it’s strong enough. Any tips would be appreciated. Thanks!
My old man used to extend the frame on road tractors, or semi's or whatever you call them in your part of the country. I even helped weld them after I got enough skill that he trusted me. He always cut the frame and the extension in a "z" so that there was more surface area that was welded. These were a "c" Channel and not square tubing.. Ive seen him do the same thing shortening a '56 Ford frame for a Falcon body. When I built race car frames, I would cut the angles for the kickups on the angle I needed and then fishplate them. These were square tube and would have more surface area than a straight cut to start with. I like your idea for offsetting the inside and outside of the cut/weld. Good Luck
Are you adding in a section and bringing the old section back in or building it from there back new ? The surgery part you’re thinking of doesn’t look out of line. I generally look at how the factory engineers do things, those with m***ive R&D budgets and requirements to meet. When they are working with multiple wheel base vehicles they have a front portion ***embly and rear portion ***embly and an adjustable mid section. The location of the connections is is certainly not in the mid section of the loads, more towards the ends. they also use a lap configuration that’s as deep as it is tall at a minimum. BIG commercial vehicles as side, the frame connection areas also incorporate some other types of larger crossmember systems to bolster the joint. Where your looking at the splice on the frame is in the middle, not ideal but your most important fish plate will be the one on the bottom, that’s the one that should be heaviest and longest over the joint because it will be doing most of the work. Where the diagonal comes in isn’t by chance. That section of main rail needed the most bolstering so the diagonal connection provided the extra umph to the main rail right there, it’s boxed and double lapped. That being said your connection is exactly where the factory engineers thought the frame needed the most bolstering. By careful planning and clever methods you can get internal plates welded in connecting the new to old and work your way out finally closing up your access window. The window would be 1/2 of the old diagonal and 1/2 in the new tube. That would be a nice bent fish plate. Doing that means you’d have to flip the red and go ahead of the diagonal with the main rail cuts and splices.
If you had some tubing that would be a fairly snug fit in the box, I’d put a sleeve in every connection so the cut would become a double frame in that area. You could drill holes in the original frame for some rosette welds to keep the sleeves from moving. Then weld up the joints and put a fish plate over the outside. It would be heavy, but strong.
I would find a LWB frame and graft that section on. Quickest way to do it Use a section of frame as a fish plate. Cut it down the center to narrow it to fit inside the rails. thsts how it’s done when you shorten a LWB frame.
Though I'm not a welder myself, I like that you will have plenty of overlap and not just a simple **** together.
I used to stagger them, leave one rail longer than the other so all the stress was not in the same plane. I also cut them on an angle for more surface area to weld to. Look at some Porterbilt stuff to get some ideas.
I've extended some frames using new metal, and done it several ways. Since your donor box tubing is the same size as the existing rails, I would do the Z cut mentioned above. But I would also add the plates inside the frame to double the thickness at all the weld joints. Simply make your Z cut, then drill 1/2" holes behind the cuts so you can plug weld the plates in place. Then once the plates are secured, drill holes in your new rails to allow them to also be plug welded. Put the rails in place leaving a small even gap so your welds will weld to both the existing frame, and the plates. This could be done with fish plates over the outside also, if you don't mind seeing the extra plates on the surface vs. hidden inside the rails. edit-Looks like from your other thread you're already proceeding with the frame anyway. So forget this reply.
I extended the frame on my '53 Chevy pickup king cab conversion by splicing in pieces of rectangular tubing. The tubing slipped perfectly over the frame rails. I cut the frame in the middle, boxed about 6" on either cut end and welded on the tube with angled welds. Worked great.
Directly from the horse's mouth. See instructions on pages 2 to 5 from GM's body upfitter guide. https://www.gmupfitter.com/wp-content/uploads/2021/06/2018_Ch***is_BstPrac_093017.pdf
I had one of those trucks years ago. I found a 1 ton ch***is of the same vintage to use the frame. 1 tons have a normal C channel frame, and leaf springs in the back, and coils up front, not the torsion bars. Too late for you now I suppose, so I will suggest this...on all the truck frame I have done, several , I weld up a couple pieces of iron at a 45* angle to use as the guide for the torch cut. That way all cuts are exactly the same. As mentioned above, the pro truck builders use a 45* cut on steel frames, and an L shape on aluminum frames. Tack it, check for straight with a string line. I got one with a slight sag in one rail once, and the truck always had a lean to one side.
Something you might think about........the rear extension does not have to be in the samr plane as the original frame. Kinda like doing a "back half" set up on a race car. You could put a cross member in the frame where you cut it off, and then attach your box tubing slightly further inboard......negating the need to try to get two different shapes to fit each other and look nice. I'll attach a couple of pictures of a frame I modified. In this case I had a long bed frame and needed to shorten it. I cut the home fabbed crossmember so the frame rails slid all the way thru and could be welded front and back to the crossmember. Then added some plates to make it strong as well as look nice. You could find another frame to pirate a back half from or use the box tubing if you like. It also gives you more room for tire clearance if you want a wider rear tire or even dually tires. and the much stronger box tube trailer hitch...........
How you do it depends a lot on your welding skills. A professional welder could weld it with a simple **** weld and it would be as strong in the weld as it is anywhere else. But that is a professional welder. My skills at flat welding are great, my skills on welding uphill and down hill are ok, my skills welding upside down …..****! I see this sernio all the time with the skills of “welders” lol I would cut it diagonally weld it together with the same size steel. Weld it the best I could, put a diamond shaped fishplate on both sides and then add a strap on the bottom connecting one or two welds , with the strap protruding out just enough to get a good weld! Bones
On the Chevy truck board I am on we were discussing shortening a long bed frame and one of the guys suggested making the cut as an overlap. Then plating and boxing thearea where the splice was. He put the plate on the inside of the rail, then boxed it in that area.
The last one I helped with was an OT Ford Ranchero on a Ford 4 x 4 ch***is. It had to be shortened, but the mechanics of putting it together are the same. This was done on a driveway, bitter cold winter in a portable shelter. The pieces removed from the donor ch***is were used to plate the cuts. We had plumb-bobs going, everything but a laser level. It was strong and tracked straight when finished. We did rosette welds too.
This was the method Pop used that I called a "Z" cut above. Thanks for posting the pic, it makes it a lot more clear.
Never done a newer truck but did several older frames. I always have added the stretch then fish plated the stretch and finished it off with a boxing plate for added strength and a cleaner appearance. To date no failures.
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