Mandrel or Rotary Draw bend for MSA cage?

  1. rcx132

    rcx132 Philip

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    Does anyone know the difference and which one is used for safety cages? They both give different bend radius. I think the workshop prefers rotary draw bends.

    I'll be using 2" x 14 swg tube (~50mm x 2mm). They will probably get done on an NC machine as that seems to be the most cost effective way.
     
  2. pedrobedro

    pedrobedro Man at Matalan

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    MK engineering used to do chassis and cages with a mandrel bending machine and the bends were perfect with no flattening of the radius. They did exhausts as well this was when I was doing my Locost. They are still on the web but their site looks like it is under construction.
     
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  3. graffian

    graffian Seer unto the end of his beard

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    Mandrel bending is rotary draw bending with a mandrel.
    They give the same radius if you use the same dies.

    When I made my first chassis the hoops were bent by Specialised Exhausts
    in Mitcham, one of the few places at the time that bent tube for people and had a mandrel
    bender. My cds was bent without a mandrel.
     
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  4. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

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    A mandrel fits inside the tube to ensure it doesn’t collapse when been drawn around the die.
    Used for thin wall tubing, and to stop necking.
    Plenty of videos on ut
     
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  5. rcx132

    rcx132 Philip

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    Ok. I've seen benders which push the tube into shape, and others that run a roller with a mandrel, I thought that was the difference. The shop that's doing my chassis sent me a list of the dies they have and there's two lists with different bend radii, one called Mandrel and one called Rotary Draw.
     
  6. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

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    Location:
    East Yorkshire
    The tighter rad bends will need to be supported by a mandrel, to stop the above
     
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  7. graffian

    graffian Seer unto the end of his beard

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    The bloke bending my tube did give me some figures and for the CDS i was using a mandrel was not needed if the bend rad was greater than 2.25D.
     
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  8. rcx132

    rcx132 Philip

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    1,831
    Location:
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    So of the two bends the fabricator workshop offers, only the one labelled "Rotary Draw" is MSA legal as the other one is too tight (MSA rule K.1.4.3 "bend radius must be at least three times the tube diameter")

    The cage will probably get professionally done, I found an affordable cage guy with a CNC machine.

    I'm not sure what to do to get the suspension done, it's a bit tight around the panhard bar which needs to squeeze between the front axle and tie link. I've got the design drawn in CAD, but the CAD drawings are +/- 5mm so the suspension has to be done by someone who can test and adjust the drawings a bit as they go - basically an affordable fabricator with a brain. Otherwise the suspension is very simple, solid axles on simple straight links. I'd do it myself but looks like I've got a 6-12 month work assignment coming up, so I won't have time.
     
    Last edited: May 17, 2019
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