weld plates for cage

[RacerBill]

No, this is not another thread on what's legal, what's not, and what is gray. I would like opinions (sound engineering will get more brownee points) on the best shape for my 100 sq inches. I intend to weld the plate to the floor, then up the side of the rocker box, and then over the top of the rocker (two total bends, in GCRese). Do I leave the plate 10x10, or do I make it 12x8.33 or 14x7.14 or 16x6.25? Cage will be 1.75 tubing.

The rockers and frame rails are being replaced, so they should be plenty strong. My initial thought is to extend the plate as far across the floor as I can.

Thanks for your thoughts.



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Bill Stevens
Mbr 103106
BnS Racing
83 ITA Shelby Dodge Charger

[Speed Raycer]

Tie to the rockers and other structural elements (frame rails, cross memebers) first, then tie into the floor. The floor is the weak link.

12" along one side is your max. Doesn't matter if there's 2 bends in that 12" side, its still 12" when flattened

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Scott Rhea
It's not what you build...
it's how you build it

Izzy's Custom Cages

[joeg]

Follow Scott's advice and emphasize the rocker structure rather than the floor.

[lateapex911]

And I would weld my tube to the vertical section if possible.

Caveat: I am speaking as a Holiday Inn expert, not a degreed engineer...

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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[Knestis]

Like Jake says, you want to maximize the weld area of the joint between tube and plate.

Putting the tube into a plate at 90* to a flat surface gives you a welded circle: Cutting a step into the tube allows you to weld it to the floor plate around half its circumference, to the top of the sill around its other half, and up the (essentially) vertical side of the sill - making for a WAY longer bead length.

More weld area for the same joint = stronger structure.

K

[RacerBill]

Guys: Thanks for the input! You have confirmed my thinking on the subject. I didn't think about notching the vertical sections of the tubes and weld the top of the cut to the top of the rocker, bottom of the tube to the plate on the floor, and then weld the vertical section of the tube to the vertical section of the plate! But I still have one question. I am limited in dimensions by the width and height of the rocker, let's say for example 3" x 3". If I were using a 10" x 10" plate, that would leave me with approx 6" of plate going out from the base of the rocker across the car. Would I be better to lengthen the front to back dimension and shorten the lateral or lengthen the lateral and reduce the front to back? If I lengthen the front to back to 12", then I could position the down tube to the extreme end of the plate and put in a short brace from the tube to the far end of the plate (seen that somewhere before!!!). If I lengthen the lateral dimension, that would add strength across the car.

Side question here. I know that with a bolt in cage, you need plates on the opposite side of the area you are bolting to. Can you use backing plates when you weld in?

Thanks for the advice. It is really helpful.



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Bill Stevens
Mbr 103106
BnS Racing
83 ITA Shelby Dodge Charger

[joeg]

Lengthening the plate on the floor will not add much strength for you.

As for "sandwiching" or doubling your plates ala a bolt-in, that is sort of a useless addition of weight. Your move into the vertical structure will do far more for you than worrying about the floor.

Cheers.

[lateapex911]

Agreed, place the emphasis in material on the vertical section and at the bends of the rocker box, as it is my thinking that you will be attaching to the area that is most rigid, and can transfer loads to the chassis in the most efficient manner.

Secondly, and again, remember I stayed in a Holiday Inn last night (!), I try to build the tubes for an "interferance fit" when possible. That is, you might need tools like jacks or large levers or hammers to push the downtubes up against the A pillar, or the roll bar against the roof. I feel it results in the most roomy configuration, and to a small degree, there may be a little safety and stiffness gain.

Finally, be very careful when welding those plates to floors and rockers, as the thicknesses of the two surfaces are very different, and it is possible to burn thru the thinner material, which of course, results in zero strength!

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Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]

[Speed Raycer]

Just don't weld it like this:



More pics:
Super Production Miata

[This message has been edited by Speed Raycer (edited March 03, 2005).]

[RacerBill]

Look's more like Clyde's cage - you remember Clyde, Clint Eastwood's friend?

Seriously, I have never welded and do not intend for my first venture being a cage! And I do thank all who responded. I respect your knowledge (even if I did decide to build and not buy! Sorry, but although it has been tough, I am getting real satisfaction that I know how to take just about everything off the car and put it back on! I remember Tom Cruise on time on a talk show was asked about his race car - he replied that it had four tires, three pedals, and a steering wheel, and that's all he knew about it!)

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Bill Stevens
Mbr 103106
BnS Racing
83 ITA Shelby Dodge Charger