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Thread: steel rollcages on aluminum chassis

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    Senior Member fatbillybob's Avatar
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    Default steel rollcages on aluminum chassis

    What is the prevailing wisdom of cage building Steel cages on aluminum Chassis? The way I see it there may be at least 2 primary theories.

    1st is to weld aluminum plates with captured steel nuts onto the Aluminum Chassis. Then the cage feet are bolted to the captured nuts. For a more permenant install what is the current epoxy for bonding the plates during bolting? I have some concerns welding aluminum backing plates to an aluminum chassis. Corvette for example uses at least 3 different alloys of aluminum in its multi component aluminum sections of the C7 chassis. They do this to be less compromising in desired structural engineering. The heat from Welding can change the local properties of the aluminum chassis in unintended ways that are not good. So that is a concern.


    A second way is to build the cage so that the seat frame is part of the cage. So if the car disintegrates around the cage the driver is protected. With that design the cage footings don't need to be as robust. With this design one would use grade 8 rivnuts into the aluminum chassis and epozy bond and bolt the cage.

    In both cases is there an epoxy that not only bonds but insulates the aluminum from the steel to reduce galvanic corrosion for the dissimilar metals?


    Brazing is strong but not as strong as welding. Is anyone brazing aluminum to steel combined with bolting?

    Has anyone used or use at work explosion welded "bimetallic transition inserts?" IMO this is the way to go. Using a BMTI in simple plate form means you can conventionally TIG weld your cage as if you had a steel chassis. I can't google anywhere to buy say 3/16" plates of this magic stuff. Any help from the engineers??

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    http://www.trackhq.com/Banners/yellowsitesponsor.gif Blackbird's Avatar
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    Working currently on an Audi TT-RS, front 2/3 of the chassis is Aluminum and the rear 1/3 is Steel. Pain in the butt
    Are you planning on caging some Alum car?

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    Senior Member fatbillybob's Avatar
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    Quote Originally Posted by Blackbird View Post
    Are you planning on caging some Alum car?
    Well mostly want to be prepared. Aluminum is finding its way into more and more chassis as the tech for aluminum is getting cheaper and better and the OEM's quest after every bit of fuel economy. The side effect is better performance and lighter for us. I have experienced a bolted Ferrari challenge cage on the early steel chassis 348's. Those cars were flexible like wet noodles. Then I experienced the same challenge cage welded to meet SCCA rules of that era. There is a huge difference in the chassis feel bolted Vs. welded. It would take a much more robust bolted design to achieve the stiffness of a simpler welded design. Perhaps even negating some aluminum chassis advantages due to added weight. Maybe a structurally adhesive bonded and bolted structure would give (at least temporarily) that welded feel. The bonding of vette plastic to chassis sure seems stiff and if you left one corner of the car with a jack the chassis does not yield like a flexible Ferrari chassis of similar vintage. Then it takes little effort to bond when bolting. I figure there is probably some research of materials and film thickness to not only bond but insulate against the galvanic reactions. Or maybe there is no consideration given to this since racecars have a relatively short service life. Then in the SCCA GCR's brazing is an accepted method with caveats. I have not found brazing rods for aluminum to steel but aluma-steel claims "welding" of alu to steel with their rods but not structural application. The little I have looked into this the more it peaks the curiosity.

    Doing that audi may be a pita but success proves a builder of a higher level... so kudos to you. There are builders out there on steel that really should choose another profession or got drummed out of other commercial welding and ended up in raceshops that have no regulatory or licensing "check and balances."
    Last edited by fatbillybob; 08-12-2017 at 01:17 PM.
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