chrisg
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| posted on 30/9/07 at 09:21 PM |
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Deciphering Marks long, rambling and comprehensive answer, I deduce that he favours the use of 4130 steel tubing or "cromolly" as
it's known.
Bit dear - is it absolutely neccesary?
What about gas pipe?
Cheers
Chris 
Note to all: I really don't know when to leave well alone. I tried to get clever with the mods, then when they gave me a lifeline to see the
error of my ways, I tried to incite more trouble via u2u. So now I'm banned, never to return again. They should have done it years ago!
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DIY Si
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| posted on 30/9/07 at 10:32 PM |
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If you want really light, then 4130 is a good bet, but will lighten your wallet to a much higher degree! If you want to make it for less, would normal
seemed tube be ok, as it is with square, or would CDS or the like be better?
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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nasty-bob
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| posted on 1/10/07 at 07:24 PM |
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T45 is superior to chromoly and does not require heat treating. It has a UTS of about 800MPa compared to about 400 for carbon steel.
But my reasoning tells me this is only an advantage on parts that might see a one time high loading- suspension and roll hoop. Here you can reduce
wall thickness and maintain safety factor.
With the chassis itself, it's loading is not one-off peaks but long term cyclic loading. So here we use the yeild strength of the material in
stress calculations, which is about 200MPa for all steels.
The extra money that would be spent on posh tube would, IMHO, be more wisely spent on lightweight products elsewhere.
I'd make it out of ERW and spend the saved cash on machining some nice uprights
Cheers
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Lippoman
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| posted on 2/10/07 at 02:10 AM |
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A frame/chassis would most likely be designed on stiffness where the Elastic Modulus is the factor. This is around 200 GPa for steels.
The yield strengths for steels vary as much as the tensile strengths. (200-2000 MPa on grades I know)
Another factor to take into account is elongation, I'd like high elongation so the parts bend/stretch instead of "snapping" in part,
easier to spot a frame that is "about to fail"...
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