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shorten a truck frame

Discussion in 'The Hokey Ass Message Board' started by chopshopboss65, Apr 6, 2006.

  1. chopshopboss65
    Joined: Apr 4, 2006
    Posts: 75


    what is the best way to cut a frame to shorten it, straight up and down, at a angle, or notched?


  2. tommy
    Joined: Mar 3, 2001
    Posts: 14,763

    Member Emeritus

    I took 11" out of a suburban frame. I cut it striaght and square.

    Sometimes people confuse glueing (as in wood) with welding. Glueing requires surface area.

    Welding does not. A properly executed weld will be stronger than the parent metal. The important part of that statement is...properly executed. Bevel the joint for 100% penetration. Unlike glueing there will be no crack remaining after its welded correctly. If the weld is a bridge across the old joint, it was not done right.
  3. porknbeaner
    Joined: Sep 12, 2003
    Posts: 38,674


    I always cut 'em at an angle, but that's the way I learned to do it. I've seen 'em done both ways and both have held up just fine.
  4. RacerRick
    Joined: May 16, 2005
    Posts: 2,750


    I am lengthening a frame in a few weeks and have been told that putting a diamond shaped plate over the weld and fully welding that is a good idea.
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  5. chrisntx
    Joined: Jan 20, 2006
    Posts: 1,787

    from Texas .

    Modernbeat sez the diamond is old technology. He sez to apply a square or rectangle with welds running across ONLY. I dunno. Ask him. :)
  6. eberhama
    Joined: Dec 19, 2003
    Posts: 615


    I straight cut mine, and plated the inside with a rectangular plate. I had a certified welder do the welding though. I think it will hold just fine, but haven't had it on the road yet.
  7. tommy
    Joined: Mar 3, 2001
    Posts: 14,763

    Member Emeritus

    I put a diamond gusset over the weld on the inside mainly beacause it doesn't hurt and I think it looks cool.:D (I ground the weld smooth on the outside so it could not be detected) It was a 3/4 ton 4X4 and last I heard it was still pulling the mountains of West by god Virginia.

    You can cut it in a zig zag. That doesn't really matter. I'm just saying that how you cut the frame will have no effect on the strength of the joint with everything else remaining the same. So why make it harder on yourself?
  8. deuce295
    Joined: Dec 9, 2005
    Posts: 211


    A weld is normally strongest when loaded in shear as opposed to tension. Granted the weld is going to be stronger than the parent metal if done right but the stress loads are handled better in a shear joint. Thats the way a splice in an aircraft fuselage is required to be welded (angled rather than straight up and down) and we have been doing it that way forever. Could be wrong I guess but just my 2 cents. I'm sure a straight cut with a welded doubler plate welded length wise will be easily as strong as the rest of the frame.

  9. chopshopboss65
    Joined: Apr 4, 2006
    Posts: 75


    thanks all just needed some input to make myself feel better before i did it. i broke the frame on my work truck and we weld it back and plated it on the inside, they burned a couple holes in it and welded those closed, i tow all sort of cars and trucks with it and still doing good.

    thanks again

  10. bigdog
    Joined: Oct 30, 2002
    Posts: 397


    When the frame on my big truck('68 Chevy C-50) was lengthened for the installation of the tilt bed they cut the frame straight, welded, then plated over it. If you look at the big commercial trucks this is how they do them. If it's sturdy enough for the loads they haul nothing we do is going to break a frame done that way.
  11. The OEM seams are always vertical,
    not at an angle,or with reinforcing plates.
  12. Am I missing something?I've never seen an O.E.M. frame with a joint in it.

  13. You're dead on! And that's the reason for diamond shaped gusset plates straddling a vertical joint. (When working with truck frames a vertical cut line is more precise, easier to control, and quicker.) The diamond shaped plate insures that the welding is in a (nearly) horizontal orientation and thus loaded in shear. Any commercial truck body company that I've dealt with always did it that way.

  14. krooser
    Joined: Jul 25, 2004
    Posts: 4,587


  15. modernbeat
    Joined: Jul 2, 2001
    Posts: 1,233

    from Dallas, TX

    On diamond gussets, just because it was done in the past, and folks still do it today, that does not make it the best method.

    The best gussett would be to flush weld the two parts of the frame together, then use a rectangular gussett and only weld the two sides that parallel the direction of the frame rails. Do not weld the two edges perpendicular to the frame.

    Now, if you've got some goal other than having the strongest, longest lasting gussett, then do something else. If you want to be "pretty" or "old-school" use a diamond. ;)

    BTW, what happened to all the old posts? I was going to link to some circa 2002 stuff, but couldn't find it.
  16. Wild Turkey
    Joined: Oct 17, 2005
    Posts: 900

    Wild Turkey

    I've seen a truck bed break because of two short vertical welds -- it was in a high stress area and the square corner caused the stresses to focus in one area ("stress riser, IIRC) and it cracked.

    Crack grew until member was broken, transfering load to adjacent members, which couldn't handle the load - - - :eek:

    That's why you only weld horizontally on frames.

    The old "diamond" was an attempt to avoid verticle welds and spread the stress.

    Anybody else ever seen a weld end with a "curlyque" -- also a way to avoid stress concentration.:cool:

    just this old welder's too scents:D
  17. RR
    Joined: Nov 30, 2008
    Posts: 67


    I know that this is an old thread but I just found it using a Google search. I have read the comments and must say, there is a lot of bad info here. First off, welds are not stronger in shear- nothing is. All metal is stronger in tension or compression rather than shear. Second, the us of a diamond shaped backing plate is not outdated. It is an effort to minimize a stress concentration. Sharp changes in the cross section of a beam- such as that caused by welding a straight plate onto a frame, will cause the moment of inertia of the beam to be sharply increased in that area. The result is that the frame is less prone to flex in that particular area pushing more stress to the surrounding part of the beam. This will cause failure. The diamond shape causes a slow increase in the moment of inertia and minimizes the stress concentration.

    A truck frame is subject to both bending and shear, with bending being the primary stress- this is why big truck manufacturers rate them with a maximum RBM or rated bending moment that is allowed in their frames. As a result, the upper and lower flanges of the frame are in tension and compression. The Z cut is the better way to splice a frame. Big trucks may cut them vertical- I have never seen that but I bet they jacket them too in that same area with lots of bolts. But the Z cut allows the most parent material at any point in the frame, minimizing the risk of a crack due to an imperfection in the welds that leads to a stress concentration. Backed by diamond shaped plates on the flanges and the web of the beam, the Z cut is by far better than a straight cut frame in a truck that is used under heavy load.
    Hnstray likes this.
  18. RICHARD TONER, president of Toner & Associates and the NTEA's (National Truck Equipment Association) first staff engineer, said "On frame splices, the general rule is that reinforcements should taper a minimum of two times the frame height. Use a straight cut at the splice. The ends of the fish plates should be tapered to reduce stress concentration in this area and Fish plates should be bolted using the match-drilled technique so the fish plate and frame act as one."
    Just some food for thought
  19. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 5,319


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