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  #1  
Old 16th November 2010, 08:52 PM
Longerr Longerr is offline
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Default 1.5mm frame thickness

Hi,

I wanted to ask if it is safe to use frame with thickness of 1.5mm, I think you use 1.63mm or so, so I just wanted to ask if it's fine to use 1.5mm thickness because in our country they make only 1.5 or 2mm

thanks
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  #2  
Old 16th November 2010, 09:04 PM
Longerr Longerr is offline
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on our first build we have used 2mm but I'd like to lower the weight of it because it has 700kg what is really too much, so on the second build we want to get as low as possible but we dont want to risk safety
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Old 16th November 2010, 10:35 PM
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According to Wikipedia, standard wire gauge is a little different from sheet metal gauge: http://en.wikipedia.org/wiki/Sheet_metal#Gauge
So 16 gauge steel sheet is actually 1.52 mm nominal, and 1.39..1.64 is the tolerance range. The next thinner gauge (17) is 1.422 mm for wire and 1.37 for sheet, so I would say that 1.5 mm is the metric equivalent of 16 gauge.

I made my chassis out of Czech made 25x25x1.5 box, black, S235 grade, but its actual thickness is 1.6-1.75 mm.
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Last edited by alga : 16th November 2010 at 10:55 PM. Reason: typo
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Old 17th November 2010, 05:08 AM
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my 130 amp mini mig struggled a bit to get a good weld on the thicker wall tube but the cheap 195 p1ssed it
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  #5  
Old 17th November 2010, 10:52 AM
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We prefer to supply chassis packs and chassis in 2mm wall thickness box section, as Adrian says it only adds about 10kg to the chassis weight but gives a stronger weld for builders and results in a stronger and rigid chassis. Especially good if you are going for the top end of the power scale, you can still make weight savings elsewhere - 700kg does seem an awful lot for a complete roadster, most seem to be coming out between 500kg and 580kg.

Regards...AndyH
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Old 17th November 2010, 06:12 PM
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If we examine a 25x25 RHS beam, 2.0 vs 1.5 wall thickness gives a 23% increase in stiffness in return for a 30% increase in weight. In other words, it adds only about as much stiffness as it adds weight.

Work it out for yourself. A beam deflection calculator is available here: http://www.calculatoredge.com/civil%...lator/beam.htm, and the weight is proportional to the cross section area, which is d^2 - (d - 2*t)^2, where d is the tube width and t is the wall thickness, if we ignore the rounded corners.

Speaking of the added weight, theoretically it sums up at 15.9 kg for 36 m of 25x25 and 14 m of 20x20.
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  #7  
Old 17th November 2010, 06:42 PM
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I know that 700kg is too much, but we did everything according to the book, but we used quite heavy 16" wheels and bmw 1.8L engine, but I dont know the weight of it, that's why we want our second build to be as light as possible, we will be using duratec 2.0 with type9, light 15" wheels and 1.5mm steel, lets see what will happen, but still 500-580kg is great with 2mm steel, I really don't know were is the problem with our car
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Old 17th November 2010, 07:29 PM
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Quote:
Originally Posted by Longerr View Post
I know that 700kg is too much, but we did everything according to the book, but we used quite heavy 16" wheels and bmw 1.8L engine, but I dont know the weight of it, that's why we want our second build to be as light as possible, we will be using duratec 2.0 with type9, light 15" wheels and 1.5mm steel, lets see what will happen, but still 500-580kg is great with 2mm steel, I really don't know were is the problem with our car
BMW parts will be where some of the extra weight is!
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Old 17th November 2010, 07:37 PM
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I really can't imagine how you ended up at 700KGs with a book built chassis, my beast has a very heavy chassis made from a mixture of 25X25X3.25 box and 60X40X2.5 box plus 16" Granada wheels and a monstrously heavy Cosworth V6 and I should be on target for around 700KGs finished (I hope ).

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  #10  
Old 17th November 2010, 08:04 PM
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It is possible that the bmw was so heavy, but the chassis must have been as well, otherwise I really don't know where can the problem be, but let's see with new chassis with 1.5mm and Duratec with t9, I hope soon (in 4 months maybe) )
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