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Okay, so it's four in the morning and I can't sleep, Partly because my wife snoors and partly because I am laying in bed thinking about the frame rails on the locost I want to build. I was watching a build thread earlier (cant remember who) and they used 1-1/2 x 1 tube for the bottom rails. That is a idea that I find interesting, It seems to make sense to use something a bit stronger for the bottom because of the beating it will take from road debris and jacking points. But then again maybe just use one inch tube of a heavier wall thickness for the bottom and suspension points and the 16 gauge for the angled bits??? I do like the idea of starting at the back and working your way forward measuring and making the frame fit the donor parts.
I will be using a 8.8 from a mustang for the rear end and a chevy 350 motor with a t5 trans. So I am thinking a heavier frame at least in the engine bay and suspension points might be good.
There is a LOT of good information on this site and I thank everyone for being so diligent in posting.
The sleeping pills are starting to kick in so I'm off to try it again.

Working late on the ECU project... There is always someone awake on this board...

Resist the urge to go very heavy. 1.25" square tube for the rails can make sense. I think .125" wall is too much. If you used round tube you have a lot more choices in sizes and thicknesses. I used 1 3/8" round tube, with .083" on the upper rail. The bottom tubes will have a little extra protection from the floor. You can add hardpoints for jacking or use a wood block to protect it.

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I know that using a round tube will result in a stronger member than using square of the same size.

I second not going for a thicker wall, you'll add weight that isn't needed, when you're really looking for cross section.

Do I ever sleep?

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Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

Walt,

Draw a circle then overlay a square of the same od. You'll see that square is stronger in four directions due to greater cross section and more material but also heavier than the same size, gauge, and material round tube.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

I guess I don't really see these as significant advantages. How big of road debris will be beating on just the lower frame rails to need the extra impact strength? Personally, I'd be much more concerned about that same debris of concern hitting the large expanses of significantly weaker unsupported sheet metal floor, than the extremely small percentage of inherently reinforced bottom area that the structural tubes account for. Similarly, jacking points can simply be selectively reinforced hard points. The lower tube intersection nodes of a spaceframe chassis probably don't even need much in the way of reinforcement to make for a good jacking interface point. Regarding reinforcing suspension points, all of the suspension failures that I'm aware of have been the result of the bracket design more than anything else.

But yes, larger tubes can also be used to increase the strength and stiffness of the chassis. More so than increasing tube wall thickness will. Personally though, I'm building my passenger compartment like a tank compared to the engine bay...As I'd rather the engine get crushed in an accident, than me.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

On the other hand, if you expect to have a proper roll cage, that will dictate the lower frame tubes. If the roll cage is the common 1.5" x 0.125" tubing size, it doesn't make much sense (practically and safety-wise) to attempt to weld it to 1" lower frame tubes.

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Awesome response, Just what I was looking for, So would 1-1/2 x 1 tube of 16 ga be better than 1 inch tube of say 14 ga?
The one inch tube of 14 ga would simplify the build and not add much weight. Although with a 350 pushing it I don't really think the small amount of weight added would matter. JMHO

Yes, imho.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Right or wrong I ran two 1x1 16ga square tubes welded together in the engine compartment.
I did this after I had built my frame when I got a momentary inspiration to maybe go with a 5.0 ford.
In the end my current engine is all I really need, but on the other hand I am glad I reinforced the frame for the small amount of weight it added.

Al

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Super Seven 3.4

Valid point, I think I was mixing too many thoughts and got them about-face...

Friends don't let friends do structural engineering while tired.

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Walt
06 RX-8 Shinka
04 RX-8 GT
06 325xi
Some people never have anything except ideas. Go do it.
Emissions & fuel economy haven't exactly been areas of strength for past rotary power plants, but absolutely no one with a soul has ever cared.

I wonder if they have a "Dummies" book for structural engineering. Heaven knows, I could use one!

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Mike - Read my story at http://twinlakesseven.blogspot.com/

They don't, confused parties are referred here for punishment. :^)

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Honey anyone?

I'm not sure that I agree with this simple statement. I think that the roll cage can be properly attached to the 1" sq tube frame. Remember, when working on a stock vehicle, it is attached to sheet metal with proper bracing of course. I think the same can be done on these Locosts. Heck, they have been done.


For more info than you'll ever need on square vs. round of various tube sizes (in torsion anyway) see this series of posts: viewtopic.php?f=39&t=8721&hilit=torsion+constants

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

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