Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Thoughts On My Crossmember Design For My Flatbed ? ( Long And Pic Filled )

Discussion in 'Center Of Gravity' started by Resurrection_Joe, Jan 22, 2004.

  1. Resurrection_Joe

    Resurrection_Joe 1 ton status

    Joined:
    Jan 9, 2002
    Posts:
    17,372
    Likes Received:
    0
    Location:
    Gettysburg, SD
    Hmm thought I'd be a bit specific with the subject there

    Anyway

    I have my 60 in, front is pretty much done

    I had previously (before an axle swap) built a flatbed on the stock frame which I had bobbed to the rear spring hangers. The bed was 66" x 84". The mounts for the front of the bed, the fi van gas tank, the rear bumper, and the tailights were all pretty mediocre from lack of experience and tools. Well, it worked anyway and I got to have one very mild mud trip and one mild rock trip before I broke a D44 stub shaft. Wheeee

    [​IMG]

    Anyway, I drug it into the shop around a year ago and hacked on it a bit, but shopped around and got some one ton equiptment from some indesicive prat named Brent /forums/images/graemlins/laugh.gif

    Well I have the rear stripped to nothing but frame and gas tank

    I know I need to have more crossmembers in, and a better tank support. I think I have the tank support worked out, as it rasies the tank (gets it away from the driveshaft and mufflers) and ties into the front mounts for the new narrowed flatbed (at 48"x84"), but as there are no stock crossmembers behind the one onder the back of the cab, I'm a bit worried about frame structure.

    It used to be open all the way to the end but for a few things bolted to the top of the frame, but I welded and boxed (in a gapped not *quite* professional way) the rear of the the frame with an old reciever hitch and some 1/4" plates

    [​IMG]

    Anywho, its a vast expanse of thin junky junk for 6 feet of open frame. As you can see, I need to add a crossmember, preferably between the foreward rear spring mounts.

    Now I was wondering how I would make a thick arse bar with square plates on the end and still be able to shove it between two fixed C channels and be able to weld or bolt it in.

    I had the idea of boxing small sections of frame and welding or bolting in the afformentioned big arse bar, but I had gleaned from various tech type hob nob discussions that partially boxing frames can put more stress on the unboxed parts.

    So I happened upon Frisbee's post about steering box bracing, and that was what i was talking about, but I THINK he sleeved the bolts so they went through the whole frame, which I can't do right at the spring hangers.

    So whats the deal, I've gotten a few suggestions, but they sound hard and involve upside down welding with the assitance from a certified kosher rabbi, and I'm not into that.

    Any thoughts?

    Also (OH NO!)

    If I build a crossmeber about where the flat plate is bolted onto the frame, can I run a steel tube from this to the reciever hitch for added strength (It's a winch point). If I can and do, should it be two bars running parralell with the fram rails, or some fun triangulated junglegym of physics?

    *cough*

    Thanks for your long enduring patience

    So uh, can we have your liver then?

    Yeah....... /forums/images/graemlins/tongue.gif
     
  2. 84_Chevy_K10

    84_Chevy_K10 Banned

    Joined:
    May 30, 2001
    Posts:
    17,669
    Likes Received:
    0
    Location:
    IL, USA
    Re: Crossmembers For The Rear Half Of A Bobbed K20 Frame

    This might sound crazy, but have you considered cutting stock crossmembers from frames and bolting/welding them in? Some frames have additional crossmembers where others do not. I think it'd definitely be worth it.
     
  3. Resurrection_Joe

    Resurrection_Joe 1 ton status

    Joined:
    Jan 9, 2002
    Posts:
    17,372
    Likes Received:
    0
    Location:
    Gettysburg, SD
    Re: Crossmembers For The Rear Half Of A Bobbed K20 Frame

    That' a great idea, unfortunatly. I dont have a ready source of that exact fram. I suppose I could see if 72 or 66 crossmembers fit, or try to get one frome a wrecked one, but getteing those damn things out was a pain in the as with a drill and punch and angle grinder with the bed off, let alone on.

    Also, for the rearward one I want to weld it to the hitch, and for the forward one, I want to have it on a curved odd part of the frame..

    I could eventually put one in th emidde of the raised part of the frame, that would be overkill but who's counting bodies?
     
  4. K1Orion

    K1Orion 1/2 ton status

    Joined:
    Jan 8, 2003
    Posts:
    812
    Likes Received:
    1
    Location:
    st.louis,MO
    Re: Crossmembers For The Rear Half Of A Bobbed K20 Frame

    [ QUOTE ]
    but they sound hard and involve upside down welding with the assitance from a certified kosher rabbi

    [/ QUOTE ] /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/rotfl.gif /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif
     
  5. Resurrection_Joe

    Resurrection_Joe 1 ton status

    Joined:
    Jan 9, 2002
    Posts:
    17,372
    Likes Received:
    0
    Location:
    Gettysburg, SD
    Re: Crossmembers For The Rear Half Of A Bobbed K20 Frame

    Well, you bastards, left to my own devices I came up with this...

    [​IMG]

    [​IMG]

    [​IMG]

    Here's Some Reference For The Frame

    [​IMG]

    [​IMG]


    More Pictures Of Current Buildup Here
     
  6. Resurrection_Joe

    Resurrection_Joe 1 ton status

    Joined:
    Jan 9, 2002
    Posts:
    17,372
    Likes Received:
    0
    Location:
    Gettysburg, SD
    Re: Custom Crossmembers For My Chopped Flatbed Frame - Long And Pic Filled

    Maybe if I change the post subject line you'll have an opinion? I just want an opinion on my design now.
     
  7. 75-K5

    75-K5 3/4 ton status

    Joined:
    Apr 28, 2002
    Posts:
    5,353
    Likes Received:
    0
    Location:
    Anderson, Indiana
    Re: Custom Crossmembers For My Chopped Flatbed Frame - Long And Pic Filled

    Here's an opinion:

    I have no idea about any of this stuff, but silver is pretty and I like all the fancy drawings! /forums/images/graemlins/peace.gif /forums/images/graemlins/waytogo.gif /forums/images/graemlins/woot.gif
     
  8. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

    Joined:
    Mar 5, 2001
    Posts:
    15,683
    Likes Received:
    1,392
    Location:
    642 Days to BB2018
    You realize of course that the only reason you even NEED that last 3 feet of frame is to hold up one end of the leafsprings???

    Maybe you should just link up the rear, and then you can just cut all that "extra" frame right outta there!!! /forums/images/graemlins/whistling.gif



    .
     
  9. Resurrection_Joe

    Resurrection_Joe 1 ton status

    Joined:
    Jan 9, 2002
    Posts:
    17,372
    Likes Received:
    0
    Location:
    Gettysburg, SD
    [ QUOTE ]
    Maybe you should just link up the rear, and then you can just cut all that "extra" frame right outta there!!!

    [/ QUOTE ]

    No, it's already built to a point where I'm going to have to learn how to drive it after it's done. I'm just working on getting it too tough to break while I flog it.

    As I've said, it's already built it far enough beyond my experience (Acknowledgement to Shaggy) and I don't need to go even farther into debt to build something someone else tells me I need.

    There's something vaugely unsetttling about being compelled to explain myself to someone based on an ever so slightly derisive offhand comment.

    Anyway, sorry if I sound impertinent

    Any thoughts on the actual design of my crossmembers (which come before the axle centerline 4 link boy) /forums/images/graemlins/whistling.gif
     
  10. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

    Joined:
    Mar 5, 2001
    Posts:
    15,683
    Likes Received:
    1,392
    Location:
    642 Days to BB2018
    [ QUOTE ]
    Any thoughts on the actual design of my crossmembers (which come before the axle centerline 4 link boy) /forums/images/graemlins/whistling.gif

    [/ QUOTE ]


    [shuffles feet and disappears back into the shadows...]

    Uh, no I guess that's all I had.





    /forums/images/graemlins/ignore.gif
     
  11. Resurrection_Joe

    Resurrection_Joe 1 ton status

    Joined:
    Jan 9, 2002
    Posts:
    17,372
    Likes Received:
    0
    Location:
    Gettysburg, SD
    [ QUOTE ]
    [shuffles feet and disappears back into the shadows...]

    Uh, no I guess that's all I had.


    [/ QUOTE ]

    Really?

    I'd think you'd be one of the people who could tell me if they were structurally sound. Specifically if they would stiffen and support the frame to the point where they would not cause the boxed parts of the crossmember (parts of themselves) to destroy themselves an pretzel my frame
     
  12. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

    Joined:
    Mar 5, 2001
    Posts:
    15,683
    Likes Received:
    1,392
    Location:
    642 Days to BB2018
    Well OK.....

    This has been covered before by Russ and others but I suppose it's worth repeating:


    Stock frame = designed to flex. Engineers expected that twisting would be a part of it's normal life, so the framerails and crossmembers were designed in a way that would allow torsional forces to be spread across LONG expanses of metal. That way, the metal isn't fatigued but it still offers the flex needed.

    When you start "boxing" a frame, or stiffening up only certain parts of a frame you are inviting problems at the junctions where the frame transitions from "flexy" to "stiff". All of the forces tend to be focused into those areas and that's where the cracks will start showing up over time.

    If you aren't really looking to go ALL THE WAY and stiffen every inch of the existing frame, it's probably better to design your add-ons so that they can be deflected and twisted slightly as well. Rubber bushings or poly would probably be a good way to keep the flex in the frame but still give you the required strength.

    Failing that, you could do the whole sub-structure design (ie. BadDog's rig, or my own prototype frame mockup) and do everything possible to triangulate the frame, but from points SUBSTANTIALLY wider than the stock framerails are....(like basically the width of the cab) Once you do that, you can run all sorts of criss-crossing braces from the rear frame corners up to the main halo, and probably get things pretty "locked down" out back. But you will still need to address the fact that everything from the cab forward is still just as flexy as "stock".....
     
  13. Resurrection_Joe

    Resurrection_Joe 1 ton status

    Joined:
    Jan 9, 2002
    Posts:
    17,372
    Likes Received:
    0
    Location:
    Gettysburg, SD
    [ QUOTE ]
    Failing that, you could do the whole sub-structure design

    [/ QUOTE ]

    Poink!

    [​IMG]

    I imagine I have the rear covered with a axle centerline shock crossmember triangulated to the rear hitch, and maybe with the downtubes from the cage if I decide to leave the top off

    For the front I dont know, the skidplate, T case crossmember, slider, and cage support substructure should do the cab area, but I dont know about the front.

    I planned on boxing the front frame rails for a hitch so that's a bit of help, but what else? Shock hoops with a cross engine bar?

    Hmm with no frame flex I may have to do those 57s and 52s I keep reading about.

    Anyway, thanks for the insight
     
  14. Resurrection_Joe

    Resurrection_Joe 1 ton status

    Joined:
    Jan 9, 2002
    Posts:
    17,372
    Likes Received:
    0
    Location:
    Gettysburg, SD
    Sorry if I sounded like I wanted info that has already been discussed. In part i did, unknowingly, but moreso I wanted to know if my design was valid.

    Thanks again
     

Share This Page