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Technical FRAME, Chassis guys - give me some feedback!

Discussion in 'The Hokey Ass Message Board' started by Ryan, Jun 23, 2003.

  1. Ryan
    Joined: Jan 2, 1995
    Posts: 21,633

    Ryan
    ADMINISTRATOR
    Staff Member

    Okay fellas, I am getting some thinking done on my rear frame 'z'. Since I am going with a spring-behind rear axle I also need to extend the chassis 7" while I am at it (to keep stock wheelbase). So, attached to this post you will find what I came up with... Total drop will be about 7 inches...

    My question to you is:

    1. Is this a structurally sound idea?
    2. Anything I should look out for?
    3. Am I dumb shit that is missing something major?

    Thanks in advance.
     

    Attached Files:

  2. Winfab
    Joined: Dec 10, 2002
    Posts: 260

    Winfab
    Member

    Make your frame cut at 22.5 degrees or you will end up with a kickup with less than the 3" frame thickness (height) on the diagonal kick section. Draw it out...I think you'll see what I mean.
     
  3. Ryan
    Joined: Jan 2, 1995
    Posts: 21,633

    Ryan
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    That totally makes sense... I knew I was a dumb ass...
     
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  4. dondanno
    Joined: Mar 20, 2003
    Posts: 679

    dondanno
    Member

    Ryan when you cut your frame cut at an angle no vertical lines the frame will be stronger. I am also going to do the spring behind but no z and will fish plate and box the area. If you have room to fish plate do it, the plate should be diamond shaped with round corners. I messured my spring location and its 7 3/4" so be extra sure. Messure 50 times cut once....Danny
     
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  5. Winfab
    Joined: Dec 10, 2002
    Posts: 260

    Winfab
    Member

    You're welcome. Only IF you had already made the cut would you be a DA! Ha!
     
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  6. Where is the axle in relation to the added piece?
    Presferrably it would be under the rear horizintal piece to give you the most clearence... I would also make sure to make a boxing plate that goes on the inside that is the shape of the entire kick up... in other words, there should not be any joints in the boxing plate... also, this may require an odd size piece of square tubing for the kick up... or you might try cutting one of the 3" sides off of a piece of 2"x3" tubing so it ends up a "C" channel... and then box it all in with a piece of 3/16" or 1/8" plate... and... what you have drawn up is going to give you 4" of additional kick up over what it was stock, FWIW.
    Sam.
     
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  7. Kevin Lee
    Joined: Nov 12, 2001
    Posts: 7,582

    Kevin Lee
    Super Moderator
    Staff Member

    Alright. Then I AM a dumbass. Here's how I did my vertical cuts and of course there is the picture I show every time someone talks about kicking a frame lately. Only difference is I swapped my bells and REMOVED 7.5 inches.

    I don't have the chi-chi labeled diagram you have but all of the basic shapes are there and you can kind of tell how I fit it together. Welded the sides first and then took a hammer and wrapped (beat) the tabs around the outsides (top and bottom) until they met up with the rails. It will have boxing plates that tie into the tubing I used to make the kicks too. Hell, you've seen it - I'll shut up now.

    Anybody care to tell me how weak my frame is? [​IMG]
     

    Attached Files:

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  8. Go here: http://www.airbum.com/NeatShtpix/RoadsterFrameSaga.html

    Look at the gusset he did.
    Simple, clean and sufficiently strong.
    Aircraft methods as noted.

    This strikes me as an excellent way to gusset over a "C" notch.
    As thin as some of them are and considering the entire weight of the car's rear half is riding on it, sure looks like there ought to be some reinforcement.

    Even if the "C" notch is boxed in and closed, that style gusset would be easy to add.
     
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  9. DrJ
    Joined: Mar 3, 2001
    Posts: 9,419

    DrJ
    Member

    I'm with what Sam said. the horizontal part "B" that has no dimensions indicated but appears short, needs to be long enough to span from the rear mounted spring to in front of the axle tubes so the axle will clear the upright parts of the "Z".
    If the frame's going to be so low that the side rails are lower than the axle, why not run the frame under the axle without a "Z", underslung?

    Grimlock,
    The angle they were talking about as Ryan drew it would have made tha added in upright piece way less than the height of the frame member. Your's accomodates that situation with the "step" cut you have in your upright. If your weld is as strong as adjacent metal and you fishplate it t should be fine on a light car. Hell, Every Fad T on the road has butt welded "Z"s in the rear.
    Do they break?
    Most of them are only carrying a 200 pound T body and interior and a 300 pound driver... [​IMG]
     
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  10. Kevin Lee
    Joined: Nov 12, 2001
    Posts: 7,582

    Kevin Lee
    Super Moderator
    Staff Member

    I'm pretty confident everything I've built so far will be fine. I'm of the "looks right, is right" school. Form and function happen simultaniously as far as I'm concerned. The airplane gusset C9 posted is rad.
     
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  11. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,254

    Hackerbilt
    Member

    I havn't checked it out completely but Budd Davissons AIRBUM site seems to have a load of good information tucked away!
    I hope he joins the HAMB...he would be a definite asset.
    That little roadster he has couldn't be in better hands!IMHO

    The guys nailed all the important aspects of the kickup...
    I just wonder if it wouldn't be cleaner to fab it with curved joints, just for extra neatness. Semi 32 style...
    Wouldn't be too hard.
    I like the fish plating idea. Done Davisson style, it would be totally cool!

    Bill
     
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  12. Ryan,

    Thanks not only for the HAMB, but for asking all these questions. I brought the sawzall home from work tonight!

    Props to all you folks that have been down this road before and are willing to share.
     
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  13. Killer
    Joined: Jul 5, 2001
    Posts: 1,569

    Killer
    Member

    In plain English:

    if you cut a piece of 2x3 on a 45 degree angle, the opening will actually be 2x4. If you cut the same 2x3 piece at 22.5 and the new piece also at 22.5, both openings will stay 2x3...

    Ryan, better idea on the kickup that attaches to the original frame (bottom piece). Notch the top of the original rail so you can slide the new piece of tubing to the bottom of the old chassis.

    A picture is worth a thousand words here cause I suck at explaining shit but my digital is broken....
     
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  14. injectedA
    Joined: Apr 27, 2002
    Posts: 590

    injectedA
    Member

    Like this?
     

    Attached Files:

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  15. Ryan
    Joined: Jan 2, 1995
    Posts: 21,633

    Ryan
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    My head hurts... Why can't any of you technical people draw worth a shit?
     
  16. sawzall
    Joined: Jul 15, 2002
    Posts: 4,721

    sawzall
    Member

    ryan..

    with somethin more like what grim is showing.. you will have more weld area..and hopefully a better chance at penetration [​IMG] [​IMG] [​IMG] [​IMG]
     
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  17. maybe you should stick to sewing?
     
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  18. injectedA
    Joined: Apr 27, 2002
    Posts: 590

    injectedA
    Member

    In that pic I posted in reference to Killer's reply, I should have removed the red and blue, as that would no longer apply. That pic was someone elses from here, I changed it. Pretty sure he means to extend thru on the lower as shown.

    A lot of you have looked at this thread. Post your ideas. I'm dealing with the same thing.

    This is the pic from C9's post. I can't do this as I'm going coilover. But it looks damn nice and strong. I am going to use the single plate idea at my front Z. There's no character up there. Looks cheap. But I think by raising the hgt. of the fin and drilling it. Maybe.
     

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  19. stevenjerk
    Joined: Nov 6, 2001
    Posts: 22

    stevenjerk

    hey saw this on 345window s website check it out
     

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  20. [ QUOTE ]
    Why can't any of you technical people draw worth a shit?

    [/ QUOTE ] Make all cuts at 22.5 degrees,this will give you a kick up at 45 degrees.AND maintain the same cross section.
     

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  21. 40Tudor
    Joined: Jan 1, 2002
    Posts: 635

    40Tudor
    Member

    Unkl Ian beat me to it, but here it is anyway - matched vs. mis-matched cut angles.

    Hmm...too late AND crappy quality... [​IMG]
     
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  22. 40Tudor
    Joined: Jan 1, 2002
    Posts: 635

    40Tudor
    Member

    Another try:

    Mismatched angles
    [​IMG]

    What I think Grimlok is up to
    [​IMG]

    While it's not all that visually appealing, I think the center gusset thru everything is structurally best with the full size boxing plate covering all the joints second best.

    As usual in structural problems, it's really a question of what you really need? They'd probably all work effectively for a light car assuming good quality welds. I could throw some FEA at it if anyone is able to estimate peak dynamic load.

    Chris
     
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  23. injectedA
    Joined: Apr 27, 2002
    Posts: 590

    injectedA
    Member

  24. Oh ya!

    That 3-d one looks to be the ticket, spreads the load out better. What would be the angles on those cuts?
     
  25. Kevin Lee
    Joined: Nov 12, 2001
    Posts: 7,582

    Kevin Lee
    Super Moderator
    Staff Member

    Yup, that's what I did. It's actually done and welded in. What I did do was leave the inside surface of the tube intact (you can see it in the photo) and am going to lap it over the boxing plate - sort of like a combination between a fitch plate and that airplane gusset. Sounds incredibly sloppy and overbuilt but in reality it's just overbuilt and not very sloppy at all. In fact it should look pretty smooth once it's done. No photos yet. I'll get some film tonight though - no digicam.
     
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  26. 40Tudor
    Joined: Jan 1, 2002
    Posts: 635

    40Tudor
    Member

    So, if I understand it right, you have a notch on the outside and just a straight angle on the inside? And the frame rails are cut square? Is the tube that you cut the notches in wider/thicker than the frame rail?
     
  27. Ryan
    Joined: Jan 2, 1995
    Posts: 21,633

    Ryan
    ADMINISTRATOR
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    shit 40tudor, what did you do the 3d drawing in? Would be sweet if the software had measurement capabilities to scale... That would make this whole mess easy...
     
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  28. 40Tudor
    Joined: Jan 1, 2002
    Posts: 635

    40Tudor
    Member

    If I assume the answers to all the above questions, here's what I come up with [​IMG]
    [​IMG]

    As far as the angles of the cuts - it really depends on what you want to end up with, but the notches are square cuts with one side cut to match the height of the tube plus a little for the radius. Hopefully the pics help explain it.

    The cuts in my pictures were carefully fudged to look kind of like Grimlok's photos and drawing [​IMG] The approach could work for any angle between 0° and 90°.

    As for strength - I think it's an improvement over straight angle cuts, but it's hard to argue with airplane guys when it comes to strength vs. weight.

    Might be a little better to overlap both sides like injecteda suggested (front and back would look like the 2nd pic above), but, again, there's really 3 things to consider

    1. How much strength do you need? ...and I'm not qualified to say.
    2. How much does it weigh? ...and do you really care?
    3. Does it look good? ...I'm probably not qualified to answer that one either!

    Ryan - All my pictures are from SolidWorks. Gimme some dimensions and I'll make you a drawing. I forgot - are you working on an A frame? If so, I'll need the height of the kick, distance from the back of the frame and an angle. If not, I'll need tube sizes and taper info, too.

    Chris
     
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  29. Ryan
    Joined: Jan 2, 1995
    Posts: 21,633

    Ryan
    ADMINISTRATOR
    Staff Member

    Rad, I will take some measurements tomorrow and get them to you. Off hand, It's an a-frame, I want between 5 and 7 inches of step and I want to extend the chassis 7.5" in the process... Because of a x-member I am using, the step has to begin about 14" from the front edge of rear crossmember where the rail is exactly 3" in height - it does taper there...

    More on that software, what is the native file format that thing exports? I've never heard of it...
     
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