mr henderson
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| posted on 15/5/09 at 03:54 PM |
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If square tube is stronger, why are most fancy chassis made from round?
From time to time I have a look around at what is out there, picking up tips and ideas, and from time to time I look at what sorts and types of
chassis people are making.
So, just as the title says, why is it that so many chassis are built of round tube?
John
[Edited on 15/5/09 by mr henderson]
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sucksqueezebangblow
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| posted on 15/5/09 at 03:57 PM |
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'Caus round tube is stronger for a given weight. Thus round tube chassis are stronger and lighter. The downside is that you need a notching
machine for round tube joints while square tube joints are just mitred.
Better to Burnout than to Fade Away JET METAL ~ AndySparrow © 
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mr henderson
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| posted on 15/5/09 at 03:59 PM |
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quote:
Originally posted by sucksqueezebangblow
'Caus round tube is stronger for a given weight. Thus round tube chassis are stronger and lighter.
If it is stronger for a given weight then surely that's either stonger or lighter?
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smart51
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| posted on 15/5/09 at 04:01 PM |
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Round tube can be run through a bending machine too, so less cutting and welding.
I used round tube because its lighter than square of the same size. It is also more torsionally rigid I believe but not quite as strong in tension.
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Liam
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| posted on 15/5/09 at 04:10 PM |
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quote:
Originally posted by mr henderson
quote:
Originally posted by sucksqueezebangblow
'Caus round tube is stronger for a given weight. Thus round tube chassis are stronger and lighter.
If it is stronger for a given weight then surely that's either stonger or lighter?
Why? Take a chassis design made from square tube. You decide to make the same design out of round tube. Depending on your choice of round tube, you
might make it just lighter with the same strength, you might make it just stronger with the same weight, or any combination between - i.e. both a
little bit stronger and a little bit lighter.
Liam
[Edited on 15/5/09 by Liam]
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nasty-bob
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| posted on 15/5/09 at 04:22 PM |
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Round tube is stronger in torsion and square tube is stronger in bending.
In theory, the centreline of the chassis is in torsion, so here it is better to use round tube, the further you move from the centreline the more the
tubes become subject to bending. So there is a point at which it is best to switch.
Of course a proper spaceframe only has tubes in tension or compression, so none of that is relevant.
So what it really comes done down to: round looks better but square is easier to build with.
Cheers
Rob
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dinosaurjuice
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| posted on 15/5/09 at 04:24 PM |
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'stronger'
tensile strength for same grade steel is CSA - therefore stronger = heavier.
strength in bending is 2nd moments of area - square profile uses CSA more efficiently
compression in slender members is also 2nd moments of area - square wins (if the diamater of round was same as square)
torsion is based around r^3, cirular section provides more efficient distribution of stress.
CSA = cross sectional area
IMO it depends entirely on how well used they are - a chassis using round should be desinged differently to a chassis using square.
Will
[Edited on 15/5/09 by dinosaurjuice]
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coozer
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| posted on 15/5/09 at 04:39 PM |
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Round tube is lighter, for any given strength so you can put more tubes in the chassis for less or the same weight.
1972 V8 Jago
1980 Z750
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kb58
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| posted on 15/5/09 at 04:52 PM |
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The issue really answers itself. Where panels attach, square is used, while round can be used elsewhere. One may be theoretically better but it
doesn't matter if it makes fabrication impossible.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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austin man
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| posted on 15/5/09 at 04:59 PM |
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Notching machine to cut joints what about using a hole saw(metal cutting type as use by sparkies) in the pillar drill way cheaper
Life is like a bowl of fruit, funny how all the weird looking ones are left alone
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mr henderson
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| posted on 15/5/09 at 05:02 PM |
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quote:
Originally posted by austin man
Notching machine to cut joints what about using a hole saw(metal cutting type as use by sparkies) in the pillar drill way cheaper
Not so good if you need a 45degree angle though.
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clairetoo
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| posted on 15/5/09 at 05:24 PM |
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quote:
Originally posted by mr henderson
quote:
Originally posted by austin man
Notching machine to cut joints what about using a hole saw(metal cutting type as use by sparkies) in the pillar drill way cheaper
Not so good if you need a 45degree angle though.
Easy enough if you have one of these 
Another point is - where do you get square CDS or chrome moly if you want a higher spec than ordinary mild steel ?
Its cuz I is blond , innit
Claire xx
Will weld for food......
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Volvorsport
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| posted on 15/5/09 at 05:27 PM |
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if you want T45 , you need to ring malcolm wilson up !
www.dbsmotorsport.co.uk
getting dirty under a bus
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Steve Hignett
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| posted on 15/5/09 at 05:29 PM |
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I have one of those!
Bought it from ebay US though and had it shipped over as a gift...
quote:
Originally posted by clairetoo
Easy enough if you have one of these
There is one on ebay ATM though!
EBAY TUBE NOTCHER
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Steve Hignett
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| posted on 15/5/09 at 05:31 PM |
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I think this is the one that I bought - he happily labelled it as a birthday gift for me...
TUBE NOTCHER FROM THE STATES
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designer
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| posted on 15/5/09 at 05:55 PM |
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All the above.
Plus, round tube chassis look better!!
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mr henderson
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| posted on 15/5/09 at 05:56 PM |
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quote:
Originally posted by clairetoo
quote:
Originally posted by mr henderson
quote:
Originally posted by austin man
Notching machine to cut joints what about using a hole saw(metal cutting type as use by sparkies) in the pillar drill way cheaper
Not so good if you need a 45degree angle though.
Easy enough if you have one of these
Indeed, that is a tube notcher. I understood Austinman to mean that you could do it without one.
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wozsher
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| posted on 15/5/09 at 07:00 PM |
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I build round tube chassis for a living,the reason square is used is simply that it is less labour intensive,it is much easier and cheaper to
manufacture.
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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fesycresy
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| posted on 15/5/09 at 07:21 PM |
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I could answer this question with all my mechanical design knowledge, all the time sitting through those boring dynamics lectures absorbing all that
information, but it can be summed up simply....
....because it looks prettier 
-----------------------------------------------------------------------------------------------------
The sooner you fall behind, the more time you'll have to catch up.
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mr henderson
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| posted on 15/5/09 at 07:36 PM |
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quote:
Originally posted by fesycresy
I could answer this question with all my mechanical design knowledge, all the time sitting through those boring dynamics lectures absorbing all that
information, but it can be summed up simply....
....because it looks prettier
I've suspected that for some time, glad to have it confirmed
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wozsher
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| posted on 15/5/09 at 07:53 PM |
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Your missing the point
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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mr henderson
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| posted on 15/5/09 at 08:05 PM |
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quote:
Originally posted by wozsher
Your missing the point
Who is missing the point, and what is the point?
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clairetoo
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| posted on 16/5/09 at 05:21 AM |
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quote:
Originally posted by mr henderson
quote:
Originally posted by wozsher
Your missing the point
Who is missing the point, and what is the point?
Theres a point ?
Its cuz I is blond , innit
Claire xx
Will weld for food......
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procomp
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| posted on 16/5/09 at 09:14 AM |
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Hi
Remember of course that the square tube dose allow the chassis to panelled correctly and act as a stressed member. IF done correctly. And that dose
add significant strength.
Cheers Matt
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Mark Allanson
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| posted on 16/5/09 at 09:29 AM |
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I have heard that the paneling adds strength - I would like to see some evidence that unstressed, flat 1.2mm ally adds anything to the dynamics of the
chassis. If it was in a 3 dimensional shape, I could see their point.
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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