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How thin is TOO thin?
Jesus-Ninja - 18/8/08 at 09:12 AM

I'm ready to order a stack of steel and start some building. YAY!

Before I do though, a question: The book chassis uses 1" 16 gauge square tube. So a wall thickness of about 1.6mm.

If one were to use a thinner wall, say 1mm (19 gauge), what would be the pit-falls, dangers, precausions, changes to design, if any?

JAG - 18/8/08 at 09:17 AM

quote:

what would be the pit-falls, dangers, precausions, changes to design, if any?


Many and varied - is the best answer. Any high stress areas would be even more highly stressed. Perhaps to the point of catastrophic failure or maybe fatigue failure.

The only way to locate these areas and check the stress levels is with an experienced FEA operator and good FEA software combined with some on-road experience with the chassis design.

Would be a lot easier to just build it like the book and trust to the experience of all those cars already built

BenB - 18/8/08 at 09:33 AM

You can get FEA software online but unless you've got an engineering degree trying to work out what the resulting figures mean might be tricky!!!

smart51 - 18/8/08 at 09:40 AM

Whilst I agree with JAG, there is scope on a seven chassis to reduce wall thickness in some areas. The clever bit is knowing where. Some parts of a locost chassis would benefit from more steel rather than less. Look for posts on the Australian mods which increase chassis stiffness.

There have been posts on here that suggest thinner tubes would be OK. I wouldn't like to advise where though.

JAG - 18/8/08 at 10:57 AM

I may have been misunderstood here

I didn't mean that the chassis design couldn't be lightened and improved upon.

Just that it would take specialist tools and a good FEA operator to do it.

If you have those tools and are/have access to a good FEA operator then go for it and let us all have a look at your results.

In the meantime, and assuming you don't have skills and software, it's easier to build as per the book.

Fred W B - 18/8/08 at 11:08 AM

quote:

Just that it would take specialist tools and a good FEA operator to do it.


Not just that, the most difficult bit is deciding what load case to design to.

Cheers

Fred W B

Minicooper - 18/8/08 at 11:26 AM

I would suggest that you use 1.5~1.6, I used to bend this stuff by hand any thinner would be just to weak in my opinion

Cheers
David

Jesus-Ninja - 18/8/08 at 11:38 AM

quote:
Originally posted by Minicooper
I would suggest that you use 1.5~1.6, I used to bend this stuff by hand any thinner would be just to weak in my opinion

Cheers
David


Going for 1.5mm

smart51 - 18/8/08 at 11:44 AM

quote:
Originally posted by JAG
I may have been misunderstood here

I didn't mean that the chassis design couldn't be lightened and improved upon.

Just that it would take specialist tools and a good FEA operator to do it.


That's what I thought you meant. I mean that whilst there is room to remove weight, you have to know what you're doing to take it out of the right places.

My 3 wheeler chassis is made from 18swg round tube and has no transmission tunnel. It is quite a bit lighter than a locost chassis, but with only 3 wheels there is less torsion to worry about.

I seem to recall that 16 guage steel is used in the locost chassis primarily for ease of welding rather than for its strength. A mechanical engineer may be able to help here but seamless tube of a higher grade than bog standard with a thinner wall may be a lightweight replacement for 16g square ERW without too many calculations.

I guess what the original author wants is a set of recommendations of which tubes can be made thinner, based on previous builder's work.

flak monkey - 18/8/08 at 11:50 AM

You can quite safely make the whole locost chassis from 18swg (1.25mm) tube.

Suspension arms etc should all be 16swg (1.6mm).

David

procomp - 18/8/08 at 02:45 PM

Hi as above ^^. 18g Westfields have been racing for 20 years. Admittedly the race chassis do have a few extra bracing in them though.

Cheers Matt

Minicooper - 18/8/08 at 03:54 PM

quote:
Originally posted by procomp
Hi as above ^^. 18g Westfields have been racing for 20 years. Admittedly the race chassis do have a few extra bracing in them though.

Cheers Matt


And a massive rollcage, most road cars won't have that advantage

Cheers
David

watsonpj - 18/8/08 at 06:26 PM

my fury has the lightweight chassis which iirc is 18swg and nothings broke yet on the chassis.

Minicooper - 18/8/08 at 06:38 PM

The only thing that concerns me is a possible accident, you may get away with less wall thickness here and there but is it worth it?

procomp - 19/8/08 at 01:46 PM

Hi the introduction of full rolcages was recent ( 5 years or so ) All the original ones just had what is regarded as STD equitment these days ie hoop with rear stays.

In some instances a good 18g chassis can have its advantages in allowing damage not to transmit past baulkheads. Proven many times in racing incidents. Obviously road situations can be different with bigger heavier objects to entangle with.

I wont mention the 20g specials that have been done.

Cheers Matt

Jesus-Ninja - 19/8/08 at 02:08 PM

quote:
Originally posted by procompIn some instances a good 18g chassis can have its advantages in allowing damage not to transmit past baulkheads.


Very interesting though. Of course with the new IVA coming in, specifically designed crumple zones and weaknesses are to be incorporated into the design. They suggest untriagulated areas, deliberate weaknesses or sock absorber / sliding piston.

Using lighter gauge for my nose section (mid engineed with central driver) with my 17g (1.5mm) providing the triangulated strong box around the driver's legs, might be something to consider.