Macca
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| posted on 12/9/02 at 09:07 PM |
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Round tube?
Is there any good reason that would stop me from producing a chassis in round tube. I except that it will take longer, but would it be as strong.
Would I be able to use the same size of steel, ie 1" round instead of box etc.
Cheers Col.
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bob
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| posted on 12/9/02 at 09:30 PM |
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i'm sure it would make panels harder to fit not having a flat edge to rivet/fix too.
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Jasper
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| posted on 12/9/02 at 09:37 PM |
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Sure it would be harder to fit them all together too, trying to cut all the angles...
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Rob Allison
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 posted on 12/9/02 at 09:44 PM |
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I can say from my experience of building a robin hood 2b that riveting to round tube is not easy. check out lolocost.co.uk there chassis is round
tube.
Rob..
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Wadders
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 posted on 12/9/02 at 10:18 PM |
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whats the reason for wanting to use round tube macca?
To produce accurate joints you will need to
be very acomplished with the angle grinder, as theoretically each joint needs to be templated to achieve a snug fit,in practice on tube as small as
1" dia most engineers would use the trial and error method,which unless youv'e had a lot of experience,error would be the norm. If you then end up
with big gaps to fill,welding will be much harder, my advice to you is,unless the round tube is free, stick to square.
Sorry
Al
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Macca
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| posted on 12/9/02 at 10:43 PM |
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Point taken, bloody stupid idea anyway if you ask me!!!!!!!!!!!!!!
Cheers Col.
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MrFluffy
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| posted on 13/9/02 at 09:16 AM |
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Why not use square for all the chassis, and then use round for the bits you can see like the cage etc? That way you only have the pain in the bum
stuff to work with for the pretty bits.
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Dunc
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| posted on 13/9/02 at 09:16 AM |
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1" round tube wouldn't be as strong as square but would be lighter for same wall thickness. A larger OD would've been beneficial to thicker wall
thickness.
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jcduroc
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| posted on 13/9/02 at 04:49 PM |
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Dunc is absolutely right.
However has anyone calculated the necessary modulus of all the tubes of a chassis? I mean, wouldn't many of the bay triangulation tubes be
sufficiently strong if round 1" (or even 3/4" in some cases)?
Questionable issue, I guess.
Joćo
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cymtriks
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| posted on 13/9/02 at 07:43 PM |
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In theory a properly designed spaceframe relies on its triangulation and not on the beam properties of its tubes for its overall torsional and bending
properties. At a more local level the need to resist bending forces caused by supporting masses such as the engine and gearbox and to provide
resistance against buckling under normal loads requires minimum beam section properties. Other factors such as weight saving, ease of welding and
resistance to minor damage also play a part. A 1 inch square or round tube in 16 gauge provides a good compromise. Using 1 inch round tube gives a
weight saving of about 22% over 1 inch square but cutting all the joints properly will be very tricky. You will also lose 22% of the torsional
stiffness which takes you down from about 1200 to 1400 ftlbs per degree for the book car to about 900 to 1100. This isn't enough as the book chassis
is only adequate as standard. In my earlier postings I outline how to double the torsional stiffness, reduce the weight and use less tubes than in the
book chassis. These mods could be used for a 3/4 inch square 16 gauge tube and 20 gauge (1mm) sheet steel chassis which would still beat the book
chassis with around 1800 ftlbs per degree of twist and give about a 30% weight saving. I wouldn't recommend such a light car structure for an engine
much heavier than a bike engine though.
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