Ball joint extenders (split from Motorsport Kit Porn thread)

Discussion in 'Chassis' started by NickBishBashBosch, Apr 8, 2012.

  1. Dave

    Dave Pedantic Old Fart Paid Member

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    Mech.

    Now't wrong with your sketch, as it gets the message over and that it what matters!

    Two points:

    I looked at similar designs using precision shoulder capscrews and, without machining most of head away, or, machining the top of the sloted part away, the head would foul the CV joint. My idea was also to use a spacer tube, like billb's design, but he beat me to it!

    You can buy rod end seals from SealsIt. I am using them on the designs for NWR's new Ibiza rally car.

    http://www.sealsit.com/rodend.asp

    Dave.
     
  2. Dave

    Dave Pedantic Old Fart Paid Member

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    Tom.

    I am saying that even a small part pen. weld would see small stresses.

    You know of the SCCH design I am sure. They weld and and use a bolt. This because the weld or bolt alone do not work. Or so I am told on another thread. I belive that is may be due to the slot in the upright 'breathing' slightly and causing a small mechanism which prises open the weld a little. Hence the need to use a bolt as well?

    For the weld to work properly, the slot should be closed to give a size for size, press fit for the shaft, and fully welded up. I would also weld at the top of the shaft as well.

    If it was not welded, and retained only by a bolt, then the effect would be just as the scenario in the first design I looked at. ie. Fatigue would be the governing factor due to D/d and r/d. Large diameter change and small fillet radius!

    Please remember these stress calcs are purely for comparrison. And, as I said in the first calcs, I have not brought shear stress into the equation. Including shear will increase stress. The Von Mieses (I believe that's how his name is speeled) formula can be used to show the overall stress due to shear and axial combinations.

    Dave.
     
  3. Dave

    Dave Pedantic Old Fart Paid Member

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    Tom.

    I am saying that even a small part pen. weld would see small stresses.

    You know of the SCCH design I am sure. They weld and and use a bolt. This because the weld or bolt alone do not work. Or so I am told on another thread. I belive that is may be due to the slot in the upright 'breathing' slightly and causing a small mechanism which prises open the weld a little. Hence the need to use a bolt as well?

    For the weld to work properly, the slot should be closed to give a size for size, press fit for the shaft, and fully welded up. I would also weld at the top of the shaft as well.

    If it was not welded, and retained only by a bolt, then the effect would be just as the scenario in the first design I looked at. ie. Fatigue would be the governing factor due to D/d and r/d. Large diameter change and small fillet radius!

    Please remember these stress calcs are purely for comparrison. And, as I said in the first calcs, I have not brought shear stress into the equation. Including shear will increase stress. The Von Mieses (I believe that's how his name is speeled) formula can be used to show the overall stress due to shear and axial combinations.

    Dave.
     
  4. Dave

    Dave Pedantic Old Fart Paid Member

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    As mech82 says we are straying off topic and it is all my fault. I did it on purpose cos. I worry that nice people might fit items to their cars without thinking of the ramifications!

    Tell you what folks. I have achieved what I set out to do.

    Which was:

    To get people looking at such things as ball joint extenders, or any other item which is critical to safety, and asking about the engineering which should go into them.

    I wonder which of these is TUV tested and approved?
     
    Last edited: Apr 14, 2012
  5. Dave

    Dave Pedantic Old Fart Paid Member

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    As mech82 says we are straying off topic and it is all my fault. I did it on purpose cos. I worry that nice people might fit items to their cars without thinking of the ramifications!

    Tell you what folks. I have achieved what I set out to do.

    Which was:

    To get people looking at such things as ball joint extenders, or any other item which is critical to safety, and asking about the engineering which should go into them.

    I wonder which of these is TUV tested and approved?
     
  6. Dave

    Dave Pedantic Old Fart Paid Member

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    mech.

    You would need to be a very skilled certified welder, before I'd permit you to weld up my ball joint extenders.;)

    The weld would need to be nigh-on perfect. Correct consumables with proper pre-heat and post-heat. Then I'd want it x-rayed.:lol:
     
    Last edited: Apr 14, 2012
  7. Admin Guest

    Thanks Daved, I appreciate the time you put in to these things and greatly value your wisdom on the subject. I am familiar with the scch design and have thought about bolt too, I imagined that the extender was inserted then the bolt tightened to correct torque, flex the slot. Then welded, the bolt would be left in otherwise the slot would try and open putting a constant force against the weld.

    The castle nut on e bottom is old school reliable mechanical locking fastener, some thing secure, would you do it differently? And use a none mechanical way to secure? Would a bolt be a better design?
     
  8. fthaimike Forum Addict

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    I thought quite a few people on here had used these without anything happening on their track/road cars:
    [​IMG]
     
  9. fredybender Forum Member

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    Track only car...
    extenders done out of 4340 TIG welded, pre-heated & slow cool down

    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
     
  10. VWralley Forum Member

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    I have ran these on my mk1 for roughly 5 years, and it is street driven to the track. I put probably 5000mi on them with no issues to speak of. I periodically nut and bolt check the whole car to be sure they never come loose. We also run them on our road race car, and have several seasons of racing and zero problems as well.

    One of the guys we race with smacked the wall at over 100mph and the wheel took the direct hit. The spacers absorbed the impact and bent, but did not break! :thumbup: VERY sturdy pieces and well worth the price.

     
  11. Dave

    Dave Pedantic Old Fart Paid Member

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    That's good to hear.

    I guess it is working like the first scenario I calculated. ie. The shoulder is close to the bottom of the upright. This calculation gave reasonably low stresses for high grade steel!

    In this design, I was more concerned with fatigue stress life than impact strength. If it bent during impact, then the stress generated must have been somewhere between Yield and UTS. If these are from a fully heat treated steel, similar to EN24 grade, then this would probably be in the order of 1000 N/mm^2!

    I note that the fillet radius appears larger than the 1mm I used in my rough calcs!? This, of course, improves fatigue resistance greatly.

    I would be interested to know how tight a fit the ball joint shaft is in the extender hole? And. Have you ever taken the ball joint out and looked for wear at the edge of the hole? Could be that with a tight fit, and the large bolt on this design, that any movement in this area is almost zero!
     
    Last edited: Apr 18, 2012
  12. fthaimike Forum Addict

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    And some original info when they were made:

     
  13. lewp91 Forum Member

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    talk about covering your own back :p

    something that is definitively required in this day and age however.
     
  14. A.N. Other Banned after significant club disruption Dec 5th 2

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    Same with all these - "off road use only" etc.
     
  15. mec82 Forum Member

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  16. fthaimike Forum Addict

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    Those are not heat treated & used a weaked steel by the sounds of it.....
     
  17. mec82 Forum Member

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    Material is roughly equivalent to EN24 so I'd say its about right, seems like the step in diameter without a decent rad is the origin of the failure. sounds lucky to get away with it :o
     
  18. Dave

    Dave Pedantic Old Fart Paid Member

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    MODS. We realy need this whole section on ball joint extenders moving to chassis under a sticky. I would hate to think of someone on CGTI having a catastrophic failure such as the one found by Mec82!

    Having read the article and checked out 4140 steel and compared it with EN24 I make the following comments.

    The steels are very similar, almost identical, but EN24 contains Nickel which adds to toughness.

    This is definirely a fatigue failure. If the 4140 was definitely not heat treated, then it should be less prone to fatigue failure. So. The failure is design related due to small radii.

    Their design, shown at the bottom of the page, with tapered sides, is better, as they appear to realise. But. As can be seen from the final page of my calcs, the stress in the shaft at the point of entry to the upright could be very large with this design if loads approaching 5kN are generated.

    I would say this is a good example of someone trying to copy what they have seen and not understanding one iota of what they are doing.

    This is why I posted the calcs!

    Note: Alloy steels require heat treatment to attain full properties. The cross section of any particular steel determines what strength can be obtained from it's particular compostion.
    High grade alloy steels, such as EN24, are usually supplied in a heat treted condition. For these items EN24T would be readily available. This could easily be treated to V contion in this size section.
     
    Last edited: Apr 23, 2012
  19. HPR

    HPR Administrator Admin

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    Attention with Welding them , at Nurnburgring being sent home at scruteneering ...because the scruteneer kept saying
    `` Guss darf man nicht schweissen ! ``
    or something as `` Cast Iron should never be welded `` ....
    No argueing allowed after a fatal crash the day before.
     
    Last edited: Apr 23, 2012
  20. vw_singh Events Team Paid Member

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    Very interesting topic. I run the black bolt on types as pictured with the radius edges and they have been fine for the years o have used them for so far. Always keep an eye on them though.

    Gurds
     

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