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Old 05-25-2005, 07:24 AM
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Frame wall thickness

I need a general wall thickness for a car frame.

in this situation it will be under a 1970 mustang, without the front unibody. 351C engine.

The whole back of the current custom frame is rusted to hell so i either want to replace that section, or redo the whole thing. Haven't done any measurements to see what it is now, but it is pretty poorly done. Id rather spend a bit of cash and build one properly, then have this POS job that i shouldn't have purchased fall apart on me hehehe

So what thickness/size of rectangular tubing should i use.

Thanks
Mike

(the one good thing about buying a car that is in WAY worse condition then you suspected, is the ability to learn SOO much from others piss poor engineering

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Old 05-25-2005, 07:39 AM
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2"x3" 0r 2"x4" and either 1/8" or 3/16" thickness. If going with the smaller tubing you could use the 3/16 for more strength.

Gary
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Old 05-25-2005, 08:23 AM
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tubing wall

Most of us use 0.120 wall tube...2x3,2x4,2x5 square main rails....0.095 or 0.120 wall for cages and hoops..Just Make it be STIFF..Safety and performance issues ya see...

OMT
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Old 05-25-2005, 09:00 AM
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I agree w/ OneMore - 0.120 wall rectangular tubing is more than adequate for car frames. It is the shape of the tubing, not wall thickness that gives you the strength. If you were to use a "C" channel, you would need to go to the thicker section but a closed tube is much stronger with less wall. You can eve drill large holes in one side of the tube for internal access and not lose any strength.
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Old 05-25-2005, 10:22 AM
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Sounding good.

The local metal shop has 2X3 and 2X4 -- 0.125 listed, so it will do just fine.

Another question.. I want to keep the original floor pans (they drop down about 6 inches below the rear seat floor, under the front seats). I would really rather not have the rails running through the inside, so what do you think bout shaping it down and under the floor pans, it will have a bunch of bends and wont be as nice as a straight rail for the middle section.

see any problems with this?

And finally, any ideas on here i can find info to draw out a frame, based on a mustang II front end? Looking at the heidts one. Where can i find info on the width of the front frame rails and such?

Thanks!
Mike
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Old 05-25-2005, 10:28 AM
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I have a buddy who is just finishing a '67 Falcon with a tubing 'space frame' built just as you describe. That is going to be one SUPER car - custom built front suspension, custom turned aluminum wheels, TOTALLY anal body work, racing/plush interior, monster 289. He is anal to the max about details and the car is a literal jewel. Been in progress for at least 4 years but he did have to take off quite a while to beat colon cancer but still, he is taking a really long time to do it perfectly.
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Old 05-25-2005, 11:20 AM
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Quote:
Originally Posted by pigman
Another question.. I want to keep the original floor pans (they drop down about 6 inches below the rear seat floor, under the front seats). I would really rather not have the rails running through the inside, so what do you think bout shaping it down and under the floor pans, it will have a bunch of bends and wont be as nice as a straight rail for the middle section.

see any problems with this?
I can think of a few...
A bunch of bends will only add flex to the rails. Every bend you make will also induce extra fatigue points into the chassis. And keep in mind these "bends" will end up being cut and welded "Z" bends. Keeping the rails straight is the best practice for stiffnes and fatigue. That's why they run through the floor. The other issue is ground clearance. If you plan on setting this car close to the ground you need to keep the frame high enough so it doesn't drag...

And finally, any ideas on here i can find info to draw out a frame, based on a mustang II front end? Looking at the heidts one. Where can i find info on the width of the front frame rails and such?
Your best bet is to measure up the car you are putting the stuff under. Use what you've got as a baseline and go from there. I don't know what the track width differences are between your '70 and a Fox Body buuuut, it may be enough to make that suspension look funny under your car... Measure the track width of the '70 and compare it to the Heidts kit.
This is a huge undertaking if you haven't done this kind of work before. I would suggest picking up some chassis design books and doing some homework before you buy anything...
Mark
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Old 05-25-2005, 11:54 AM
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Quote:
Originally Posted by astroracer
Measure the track width of the '70 and compare it to the Heidts kit.

Mark
Well lucky for me, the car as of now already has a stock mustang II welded onto the custom frame. My reason for replacing it is:

1: The jacka$$es that built this car cut the x member to take a stock oil pan DUH, so now it is soooo weak.

2: i don't trust their welds onto the frame, look pretty sketchy, Id be alot happier with my own welds.

Quote:
Originally Posted by astroracer
Keeping the rails straight is the best practice for stiffnes and fatigue.
On that note, where is the best place to put a jog to line up the track of the front IFS and the mounts for the rear end, im guessing as of now, it wont all be completely in-line (im thinking 4 link for the back, ford 9").


And finally, about books, any references, i've looked around but have yet to find anything that sounds like a bible of chassis design?

Thanks, you are all a wealth of info, couldn't do any of this without you!
Mike
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Old 05-25-2005, 02:23 PM
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Just do a google under chassis design. You'll find tons of info.
Here is a site that has a bunch of stuff and a lot of it is usable...
http://www.gmecca.com/byorc/designpu...ionsbooks.html
You really need to have a good understanding of the terms, hows and whys when reading many of these books. Don't expect to pick one up and run with it... you'll be a while just getting a grasp of the basics.
Mark
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Old 05-25-2005, 09:57 PM
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Take a good long look at drag car designs. You want to adapt and stiffen from there for your purposes. Floors will become secondary when you design and build your own framerails. Form must follow function. Plan on at least some sort of roll bar or cage as you will no longer have the designed-in stiffness of the unibody to build from. Look into getting some mandrel bent rails or even some individual bends of 2x3 and use them like building headers. The difference being to use some inner supports and rosette welds to hold it all together. You'll be so happy you did when you step back and look at it.
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Old 05-26-2005, 08:29 AM
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Quote:
Originally Posted by theHIGHLANDER
Look into getting some mandrel bent rails or even some individual bends of 2x3 and use them like building headers.

I've been wondering about this actually.. I can get this done, i know where to get it done, and can probably afford to. But is it actually worth it? Wouldnt bending just stretch the metal on one side and in turn weaken it? uin theory if i weld Z's for the frame properly,l it should be as strong as the original metal.. If i hold it in place well and make sure it doesnt warp, it should be just as good?
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Old 05-26-2005, 08:39 AM
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Speedway has mandrel bent chassis kits here and here and here
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Old 05-26-2005, 09:03 AM
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Reproduction 32-34 Ford fames are built up from 3/16" flat sheet. The sides are cut from the flat sheet and placed in a jig that forms them to the shape of the original frame. Then flat sheet steel sides are full welded on. After all the crossmembers and X frame is welded in the frame is flipped upside down and the bottom sheet steel is welded on forming a completely boxed frame which is super strong. My frame from The Roadster Shop is a work of art, it has some of the most perfect TIG welding I have ever seen. If it would not rust I would like to have left it in original metal rather than painting it.

Vince
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Old 05-26-2005, 09:30 AM
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My plan was to do something like this

Cboy's Frame

I like the way it came out.. and seems fairly straightforward?? A frame designed like this should be plenty strong shouldnt it?

Mike
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Old 05-26-2005, 10:08 AM
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Has been done probably 1,000,000 times and yes, is very strong.
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