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DaveNotSoSideways

Crush bending cold drawn steel / tubing

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Good points Nick.

 

I think also that there maybe a few rubber mounting pads still on my car, I should really get those ditched.

 

Given the option would have been good to work on this while there was a bare chassis and a big hole in the bulkhead.

 

I put alot effort into that gearbox tunnel but I could be presuaded to slice the entire middle out of the cockpit for the right design? :) Be easy to sort out the bodywork with something like what V8 nick has, you simply box up the railwork with thin alloy plating and weld the floorpan to the chassis.

 

As such this needs careful thought about every detail.

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Well you could guess the bend radii and it wouldn't be far out - as long as the basic dimensions are correct. I could have a go at it sometime - I've got a CAD license with basic FEA on my home PC...

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I dont know how long these things take, if it's too much hassle I can probably handle it but I have no CAD experience so it's a long process.

 

Could use some fixed design parameters too. As there are things in the way etc.

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I dont know how long these things take, if it's too much hassle I can probably handle it

Only do things when they are too much hassle?

That's the spirit DS. ;D

 

Well it took me about a week to learn Solidworks using the tutorials.

But that was just the basics, not stress analysis.

I guess you could draw the chassis in 2-3 weeks, if you don't have much experience.

 

F.

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I have access to CAD some quick workstations and CAD and FEA trained. Could have a go but if you can cad the chassis up using surfaces as you will need to use shell elements with something of this size and detail I could whack it onto a computer at work. Andy

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I think the best way would be if you gave me CAD line 3D sketch and I can use beam elements if the section is constant for various parts of the chassis/cage

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hi folks,

 

http://www.lisa-fet.com/

 

might be interesing for the folks who would like to get a little bit into FEA stress analysis. Even the unrestricted license is cheap, I assume they have to give it away as FEA is nowadays included in full blown CAD/CAM packages, so there is no marked for stand alone products anymore.

 

but be warned -- it seems the modeller is rather poor, so modelling anything in detail might be painful. And it seems to require some basic undersdtanding what FEA is and how it works, to get useful models and results.

 

cheers,

Reinald

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That last Vitesse, with an extra space frame welded to the chassis, would also be wasted weight, IMHO, for the above reasons, unles the owner wished not to have a roll cage.

Except, extending the roll cage forwards to the suspension turrets has always seemed a good idea to me, if that is what is shown above.

 

Joh Thomason published an article in the Courier a while ago, on the torsional stiffness of the Spitfire chassis.   He proposed two ways of making it stiffer; one, a extra cross member between the chassis rails, where they seperate under the rear footwell;  second, a pyramid of tubing inside the car, that bridged the rails, and might be incorporated into a roll cage.  I've never seen either of these mods used, but John was quoting figures taken from a real chassis in a real torsion rig.   If anyone wants a copy of the article, PM me with your email address.

 

JOhn

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I think also that there maybe a few rubber mounting pads still on my car, I should really get those ditched.

 

I've done all solid spacers and felt that made a difference.  Just welding you current cage will make a difference as would be putting a diagonal in the roof and perhaps putting in straighter door bars.

 

Tubework around the tunnel would obviously add stiffness but this would be a fraction of the stiffness that would be added if the same tubes were out in the roof, floors and sills.  In my daily business of ship structure it is the keel, turns of bilge and upper deck edges that contribute the most to longitudinal strength and transvesrse frames the torsional resistance, all metalwork on the periferies. The bits in the middle just stop the cargo from flying around. You'll get more bang for your buck the further away from the centre you get.

 

Andy

 

 

 

 

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The photo of my chassis that Dave posted was an attempt to imitate a Lotus or TVR-style backbone, partly because the chassis main rails were slimmed down to fit the gearbox and partly because the larger engine will create significant longitudinal twist on the chassis (when the wheels gain traction). The tunnel is welded to the main rails and runs from the front turrets to the rear coil-over mount points. Andy and John are right, the same amount of steel would be far better used as a roll-cage, but the New Zealand authorities restrict roll cages to competition cars - without Motorsport Association approval (and a racing licence) it couldn't be used on the road. Stupid I know - in theory you can't even put a roll-over hoop in a convertible!

 

The tunnel's not finished yet. The body restorer decided to move the engine back further - good idea, but he chopped some of the backbone out. Maybe this is what happens when you use different experts for various stages of a job, but I was pretty pissed off when I saw the photo (below). You pay one guy to build something, and the next to rip it apart again :-( When I fix it, we'll add some thinner diagonal bracing to triangulate against extension, compression and twist.

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Is that the same article as the one I posted, or does it have new insights?

 

What article?

In this thread?

Was it titled "Twisted!"?

 

I'd post it, but it has lots of pics and I OCR'd it into a 700K Word doc, that won't come through onto the MsB, I think.

Glad to email it.

Just hope JT doesn't mind.

John

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Page 3 right at the top.

And yes it is titled twisted.

 

I didn't upload it though, only posted a link to where I found it.

 

Frederick

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If I am going to weld in my current cage I might as well just remake the front to atleast have something better welded in. It's not a great design it's just easy to fit and works as a cage but no thought has gone into making it multifunctional, its just a rollcage it's a not smart solution.

 

To be honest I could ditch the front hoop over the windscreen frame..

 

I had a look it'll be hard to fit a rear cross member between the chassis rails under the box section than is just behind the heelboard cause it will be impossible to remove the prop, especially with a sliding nose as on the type 9.

 

You'd need to have the diff out and I am not expecting super life span from my prop joints till I get better joints in one. It could be made to bolt in I am sure if the mountings were carefully thought out, such as a U section of 3mm welded to the chassis on each side then a box section bolts in that has reinforced captive threaded plates inside. You'd not get anymore twist in that you would in a simple butted weld joint. Infact if you used thicker grade like 3mm for the U sections and double butted the bolt in beam would probably be stiffer. So thats an option.

 

The bare chassis test needs to be taken with a pinch of salt, they should have tested it with the body on, cause noone runs a bare chassis do they.

 

Another option is to cut out the short outriggers that are running just infront of the seats and remove them, also removing the box section from the cockpit floor and cutting a section out then welding in a proper outrigger to the chassis that is welded to the floorpan and the inner sill. Shame you cant really add another crossmember between the rails at this point... This could be linked to a new doorbar also?

 

Yes I think those doorbars have to go, to be fair they make getting out HARDER than a straight one  they are a really awful idea plus you need to cut the door to pieces :) my seat has a really high side,, it would be higher than a normal straight door bar so they are totally useless. I have to clamber over the bar cause it sticks out so far.

 

So yes they are going. I will fit a straight bar at an angle down from the rear hoop to the front outrigger, a lowish angle diagonal that links to the front hoop and also to the bars that will run to shock tower.

 

That seems like the obviously thing to start with. I can box up the front outrigger at the end thats just a U section.

 

Ta.

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Thanks, Frederick!   That version is rather better than mine as it is a full colour, pdf scan, whereas mine is an OCR version, B&W.

 

Barry,

"The bare chassis test needs to be taken with a pinch of salt, they should have tested it with the body on, cause noone runs a bare chassis do they."

You have to start somewhere, and I know that even bolting a Vitesse body to the chassis doesn't make it very stiff.

I know, because my first roll cage was frotn & rear hoops, with bars bolted on between them.

Negotiating a bumpy paddock, I could hear the bolted jopints squeaking as they moved.

After I welded them up, the noises stopped and the car just felt so much more stiff.

 

Steve,

 

Can you post that article somehow?

My scanner came with an OCR program (see above), or use a PDF maker program.

What's the advantage of autobody foam over builder's?

If, IF, the foam adheres to the inside of the sills, then extra stiff ness is assured.

In the UK I'd be worried about the foam retaining water inside the sills, causing rampant rot and the foam detaching, making the situation worse.

 

John

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Its been educational anyway, I've been thinking about this alot the last few days.  I am sure a bit more thinking can arrive at a decent set of improvements.

 

As with anything I think the main improvements are the small details...Like relocating where the cage is picking up/bolting down to.

 

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Mark, how are you knotching the tubes? I've done them before by hand but thats just painful after the first two cuts with the angle grinder.

 

I'd like to get a DC TIG with MMA/Plasma Cutter soon but till then, could use a new MIG too....

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DS - yeah a bit tedious do it that way

 

I used a pillar drill - polit hole then hole saw + flap disc

 

TIG - make sure its a HF start one though (foot pedal is nice)

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HF start is very nice. Foot pedal depends on technique I think, every TIG welder I have spoken to (quite a few) has a different view on the best way to control current.  Seems to be more necessary for ally welding (for which you need AC/DC which ups the cost stakes somewhat).  Nice to have the facility I guess.

 

Nick

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Hi Frederic,

 

I've got a collection of Chassis here, most of the usable, you could just grab one for a few bucks...

 

Cheers,

Reinald

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Body and chassis apart ATM - what measurements would you like??

 

Thanks for the offer, Mark.

I'm going to give it a try; putting the chassis in Solid Works, but I need more measurements than the drawing BS posted has.

Mainly the area under the body, I can take the measurements of the front chassis on my Spitfire.

 

I'll make a list of the dimensions I need.

 

Cheers,

 

Frederick

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Frederick,

I don't know what was posted before, but my reproduction Spitfire WSM has a very detailed chassic diagram, with 50 dimensions listed.

It's page 76.10.02.sheet 2

See below.

If you want a larger version of the pic, please remind me of your email address.

John

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