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Let's talk frame thickness, spring mounts and 'bones

Discussion in 'The Hokey Ass Message Board' started by Brad54, Sep 17, 2010.

  1. Brad54
    Joined: Apr 15, 2004
    Posts: 6,008

    Brad54
    Member
    from Atl Ga

    It seems like the cool new trend is to use split bones as the spring mount, with some perches welded to or thru the side of the bones, well back from the I-beam axle mount.

    I've got a couple questions:
    Not having a set of bones handy to measure, what is the wall thickness of the tubing, when you cut them apart?

    What's the minimum wall thickness of frame rails when you guys build a chassis? I'm gonna go out on a limb and say the wall thickness on those bones is a lot thinner than the thickness of frame rails.

    How are they compared to the thickness of the crossmembers where the springs mount?
    Spring mounts/cross members are fairly heavy, as they should be--they're supporting the entire weight of the vehicle.
    Just like the bones are when they're modified to become spring mounts.

    'bones are there simply to stabilize the axle fore/aft, while the spring and it's mounts support the weight of the vehicle. It doesn't take a lot of strength/wall thickness to stabilize the axle. Which, by the way, is that stout for a reason--as are the spring leaves. In fact, it seems like everything associated with SUSPENDING the vehicle is pretty beefy, while everything associated with steering and stabilizing is pretty spindly.

    Additionally, I've noticed that when someone mounts the spring to the bones, the axle rides way out ahead--sort of like a cheater bar on a ratchet. Leverage is a bitch. Those bones were never spec'd to hold the weight of an engine.

    Well, that's my opinion... I'd like to hear from some others on the matter. To me, it just seems like it's an easy way to stress crack/fatigue the metal, and it's only a matter of time before someone is honking down the highway and their front suspension folds like muffler tubing.

    Or am I being an old woman?

    -Brad
     
  2. Pitbullgoingpostal
    Joined: Jan 2, 2009
    Posts: 408

    Pitbullgoingpostal
    Member

    That's why it's called a suicide front end. I don't personally care for the look of the wheels way out front myself. I'm sure there are plenty of people that have engineered a strong version of this configuration, but most are just as you described. Also, the thickness of lets say Model A wishbones is only about 1/8" at best. I don't think they are 3/16". Been a while since I have cut any.
     
  3. i cut my front bones a while back, dont know the exact thickness but they were not to thin. i didnt do this setup, sice i also do not like the wheels way out front.
     
  4. <!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:punctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w:DontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--> I am building a split bones set up using 39 axle and bones.
    I would say the wall of the bones is thicker than the chassis.
    5mm for the bones and 3 mm for the 27 chev chassis.
    I like the look of the “I” beam just in front of the grill, the spring on my set up will be as close to the forged part of the bones and will use a 10mm “bracelet” that will slide on and surround the bones.
     
    Last edited: Sep 17, 2010
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  5. tiredford
    Joined: Apr 6, 2009
    Posts: 467

    tiredford
    Member
    from Mo.

    I've seen bones break in the front, you know the C part. And that was mounted in the normal way, with little weight on them.
     
  6. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,428

    Von Rigg Fink
    Member
    from Garage

    you could weld a cylinder in the hole you drilled thru the bones ,and if done right it should add conciterable strength to the attachment point. maybe even a few hard washers on each side to help spread out the load too..

    I dont care for the set up much , but im sure there's always a better way to skin this cat
    even building your own bones that are up to the task could be a better idea
     
  7. Anderhart Speed
    Joined: Nov 8, 2009
    Posts: 356

    Anderhart Speed
    Member

    I've seen this done right and wrong. Personally if you're going to do this I'd go with a new set of 'bones that are being produced right now. They are thicker and stronger. As far as chassis thickness, thats something else too. My main rails are 1/8" box tubing, but the car is fully caged with .095 4130-which is overkill. Technically I could probably thin everything out down one size (thickness, not diameter) and still be okay. Like you were saying about leverage-you have to think that way and follow where the forces are going to travel through the chassis, and size accordingly. Personally I've seen this setup done wrong more times than I've seen it done right. Although I do think it looks kind of cool.
     
  8. carcrazyjohn
    Joined: Apr 16, 2008
    Posts: 4,844

    carcrazyjohn
    Member
    from trevose pa

    35 -36 bones are the thickest out of model a or 32 or 34 fords
     
  9. langy
    Joined: Apr 27, 2006
    Posts: 5,735

    langy
    Member Emeritus

    My A bones were certainly thicker than 1/8", I didn't think to measure the wall thickness when i cut mine, chassis material is usually 1/8"
     
  10. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,284

    Kerrynzl
    Member


    One saving grace with suicide front ends [ with shackles hanging off the bones ] is they're usually on lighter weight vehicles, and moving the spring back further also softens the suspension by altering the motion ratio.

    The practice of welding the spring perches to the bones is bad engineering [ unless the bones are heat treated after welding! "which I haven't heard of anybody doing so far" ]

    Nobody would consider "cut and welding" Tie-rods or steering arms [ unless they are "strong backed" with a plate ] but the process is relatively safe if crack tested and "Heat Treated" afterwards.

    With engineering, "Shape" is more important than how much "meat" there is in the steel.
    A large diameter thin wall driveshaft is stronger than a small diameter thick wall driveshaft. Gun drilling axles dont lose any strength etc
    The problem with pushing the limits of engineering integrity is when the shape is unintentionally altered [ eg: a dent in driveshaft tubing, or it's bent and whips like a skipping rope ]
    A smart way to suicide a front axle would be to weld a couple of correctly machined "shackle pins" directly to the axle [ behind the axle, between the bones ]
    This method is normally found when somebody mounts "coil-overs" but would be successful with crossleafs
     
  11. Antny
    Joined: Aug 19, 2009
    Posts: 1,071

    Antny
    BANNED
    from Noo Yawk

    I've seen some done with gusset plates added. I like those. I don't care for the wheels-forward look either, but I think this setup can be fabricated with plenty of safety. There are lots of these setups on the road, have we heard of any that have failed? Would like to hear.
     
  12. Truckedup
    Joined: Jul 25, 2006
    Posts: 3,865

    Truckedup
    Member

    I believe the frame side rails are 11 gauge or about .125.
     
  13. fab32
    Joined: May 14, 2002
    Posts: 13,988

    fab32
    Member Emeritus

    Take a look at how Shadow Rods makes thier Bones. The front forging/casting is expended further rearward and the spring mount is through solid stock to eliminate this very issue. Check them out.

    Frank
     
  14. revkev6
    Joined: Jun 13, 2006
    Posts: 3,340

    revkev6
    Member
    from ma


    really?? you think a casting is stronger than a forging?? no way would I ever put a spring hanger on one of those new wishbones with the cast ends. I wouldn't even run those split. I would run a tube through and add couple gussets to the stock 36 and up wishbones myself.
     
  15. <!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:punctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w:DontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--> How are the bones made? Forged to shape and welded at the seam?
    The bone is but welded to forged I beam end and the same at the ball end.

    I had not considered how I would go about a bend for tyre clearance.
    I had an idea that I could fill the bones with sand, plug the end and heat to bend in the area that would make contact (tire – to – bone), then cover the bone in sand to let it cool slowly.

    ..
    .
    .
     
  16. Thats how I built mine, thickwall DOM bushing welded to the forging AND the tubing, split the difference. Also allows some movement of the perch to eliminate binding.

    Brad, I dont have a set of cut bones at the moment but they are thick.
     
  17. Why worry about tire clearance? It is a moot point on most cars. If they touch it is only at full lock. If you are at that point on the road you are probably have bigger worries, like the ditch, getting the car out of the spin etc:D
     
  18. R Frederick
    Joined: Mar 30, 2009
    Posts: 2,660

    R Frederick
    Member
    from illinois

    I didn't want to weaken mine by drilling or cutting, but rather structurally enhance if anything. I made a hanger for my spring perch on my bucket.
    [​IMG]
     
  19. Brad54
    Joined: Apr 15, 2004
    Posts: 6,008

    Brad54
    Member
    from Atl Ga

    I understand what guys are saying about reinforcing the mounting area... but what about the rest of the bone? It's not like the forces are any less along its length. The reinforcement is going to strengthen the area area where the spring mount is, which will keep it from tearing out, but will it keep the rest of the bone from cracking if it takes a shot from hard pot-hole?


    -Brad
     
  20. squirrel
    Joined: Sep 23, 2004
    Posts: 44,285

    squirrel
    Member

    Actually the bending load is quite a bit less along it's length, decreasing to zero at the back end of the bone.

    On something like this, stress due to bending load is usually higher than stress due to shear load.
     
  21. Bib Overalls
    Joined: Aug 3, 2001
    Posts: 4,068

    Bib Overalls
    ALLIANCE MEMBER

    Front bones are incredibly strong. They are designed to take the torque generated by the brakes. Imagine the forces at work hen a 3,000 pound vehicle is panic braked.

    Rear bones were designed to hold the rear axle square to the torque tube. The forces on them are pull and push. They don't have to be as strong as the fronts and Henry did not waste any material on them.
     
  22. rancid737
    Joined: Feb 22, 2011
    Posts: 219

    rancid737
    Member

    So I've got a pair of 47-48 Ford dogleg split wishbones that I was thinking of adding two 1/4 inch plates (see red area in pic) with a chunk of DOM tube for the spring perches for a spring-behind setup. Anyone see any issues with this?
     

    Attached Files:

  23. titus
    Joined: Dec 6, 2003
    Posts: 5,039

    titus
    Member

    I drill the wishbone for a spring perch to go thru, when i drill them i do it right up close to the forging, actually one side of the whole being the forging, then i weld the perch bolt in, to the wishbone and forging, i highly doubt it would ever break, nor need to be reinforced, the pic attached is a bit further from the casting but i put 1000 miles on this car the first weekend i finished it and then another 500 before i sold it, its now out of the country and has been for 3 years and has many many miles more and no problems, the pic here is also just during mock up, i cut the end of the perch bolt off so it sticks out about 1/8 of an inch and weld around it.

    Also regarding the thickness, all the bones are basically all the same thickness, i had some cut up A bones, and 32 bones and 34 bones and 40 bones and we took a mic and measure them all, they were all basically the same measment, not enough of a difference between each other to call different. and if i remember correctly they are the same or thicker than the frame metal thickness, i can really back it by any numbers cause i dont remember and it really never mattered, we just measure the stuff to end an argument.

    jeff
     

    Attached Files:

  24. rat pup
    Joined: Jun 8, 2009
    Posts: 142

    rat pup
    Member
    from houston

    titus has a good idea
     

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