Just thinking out loud again. I read somewhere that a rule of thumb limit for tubes in a space frame was a wall thickness a 50th of the overall
diameter. 24 gauge steel is 0.511 mm thick so would be suitable for 25mm OD tubes. These have an area of 39.3 mm2 so with a tensile strength of mild
steel would yield at 1600kg. plenty for a kit car chassis. Now assuming you could successfully weld steel that thin and assuming your space frame
was fully triangulated in 3 dimensions, would such light weight material be OK for use in a chassis (in areas where a direct load was not applied,
such as suspension pick up points)?
[Edited on 18-12-2009 by smart51]
quote:
Originally posted by smart51
24 gauge steel is 0.511 mm thick so would be suitable for 25mm OD tubes.
The additional amount of triangulation to obtain strength would probably weigh in at just as much as usingnormal stuff....
The problem is that a pure tensile load doesn`t exist except for a really good design.
This good design will have no passenger space.
So it will take bending loads as well, hence be very weak in this aspect.
Darren
I've got a broom handle made of 24 gauge steel the we use round the work shop and it's bent from use, does that tell you any thing?
you've got fat hands?????
(my wooden ones are bowed from over enthusiastic use)
[Edited on 18/12/09 by MikeR]
Mike R - You have wooden hands!!!!????
Even 20 guage tube has a habit of cracking & breaking away fron welded points, for road use I wouldn't be inclined to go much thinner than
the 16g we all normally use. Thinner might be ok for racing where it's going to be regularly inspected & not used daily & where you
expect to carry out maintenance & repairs fairly regularly.
Something which you can leave alone & forget as with a daily driver needs to be more durable.
quote:
Originally posted by Talon Motorsport
I've got a broom handle made of 24 gauge steel the we use round the work shop and it's bent from use, does that tell you any thing?
Lower then 1.2mm is not a good idea.
If you want to go to the limit, you must think of other welding methodes.
And laser-fit cutting.
Around the wishbone brackets, engine mounts and safety belts 1.2 mm will be hard to use.
So, I will stick with the 2.0mm for mine.
Hi
5 or so years ago it was perfectly good to do a 20G race chassis with the usual extra triangulations Etc.
But in this day and age the quality of metal is bad is getting beyond a joke. You would not entertain trying a 20G chassis with today's quality.
and dont forget that all Well un certificated tubing anyhow is all down on Min tolerance. So even a 16G chassis is actualy 17.2G
Cheers Matt
1) the right size tube is the right size tube
2) Some tubes are in tension, and some are not
3) there is more than one way to fail a tube
4) Even if a tube is OK for static strength, it might not be for durability (fatigue).
5) sometimes even if you make a model, or do a fancy calculation, the size is still wrong; time will tell.
Uncle Kenny, the Engineer
quote:
Originally posted by smart51
... Being an engineer but not a mechanical engineer, I don't know how thin you could go and it still stand up to road use but from what I've read, 24 gauge tube with plenty of triangulation fits within what seem to be usual guidelines.
quote:
Originally posted by kennyrayandersen
1) the right size tube is the right size tube
2) Some tubes are in tension, and some are not
3) there is more than one way to fail a tube
4) Even if a tube is OK for static strength, it might not be for durability (fatigue).
5) sometimes even if you make a model, or do a fancy calculation, the size is still wrong; time will tell.
Uncle Kenny, the Engineer
Iv'e always wondered how much strength you loose with all the rivet holes for panels in a 16G chassis. I bet the same holes in a 24G chassis would be a problem.
it's a bit of nonsense as KB58 pointed out. There ont enough data in the question to even estimate a reasonable solution. Now, if you were to say book chassis tube XXX with this engine and that whatnot and you could proabably use 3g's for over-the-road vehicles (this is what the big rigs use anyway (I read a book once...). Off road vehicles use a g-factor of 5. Then you could start summing the forces and moments, or build an FE model. Use that to get the loads. Then using those loads you could do a buckling and crippling check as well as a net section check (section less all of the rivet holes) and this would be for ultimate loading. If you sized it for these factors, and used steel for the material dejour, you could take a stab at what gages you could use. I rarely see all that done though...
OK, I think I need to point out that I'm not planning to make a car from 24 gauge tube let a lone a locost, I'm just trying to start a bit
of informed debate. Clearly, dent resistance would be a problem, particularly for tubes under compression load. Drilling holes for rivets would be a
bad idea too. Cymtrics recommends welding in sheet steel panels in places, rather than diagonal tubes and as a 0.7mm steel floor is the same weight
as 2.0mm aluminium and adds more stiffness, welding would be the way to go.
I reckon 18 gauge is plenty strong enough for a locost with 20 gauge in places. The car I had in mind would weigh about 350kg and have 20 BHP and I
suspect that 20 gauge all round (in certified material) would be plenty.
quote:
Originally posted by turbodisplay
The problem is that a pure tensile load doesn`t exist except for a really good design.
This good design will have no passenger space.
So it will take bending loads as well, hence be very weak in this aspect.
Darren
Donkervoort used to use 1.5mm tubing. Laser cut and brazed together though. Don't know what they are up to now, it's been a good 5 years since i've been to the factory...