I am looking at spot welding steel panels to the chassis (including the side panels) as the whole car will be painted and I would like the extra rigidity.

Firstly, would the spot welds me strong enough compared to rivets (looks neater too as I can fill/file to get the surface level prior to painting)

Secondly what sort of weight difference wiull there be? Is it really going to be a problem for a car than isn't going to be raced?

One question Why? Why do you need to add 'extra rigidity'? Are you using a Merlin engine?

Cheers

Steel weighs 2.9 times as much as aluminium.

From my calculations a 1.6mm ali side panel weighs about 2.8kg. So the same in steel would be about 8kg. But you could get away with using a thinner panel, say 0.8mm steel so it only weighs 4kg. The difference in strength of a 1.6mm ali panel and a 0.8mm steel panel wont be much. But the steel will weigh half as much again.

I can do the same thing for the other panels if you want. But you are probably looking at 10kg extra panelling the sides and rear in (thinner) steel rather than ali.

Cheers,
David

quote:

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Originally posted by chunkielad
I would like the extra rigidity.

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The reason for adding rigidity is I don't know the person who welded the chassis. Although I am sure he is very competent, I thought that if I made boxes with steel, it'd be stronger generally.

The main reason for steel however is that I can spot weld it and get rid of the rivets totally. This will allow clean lines when painted.

I am not so much bothered about the strength really just the extra weight and if it'll cause any problems.

I was thinking of putting 18guage on but 20 guage may be better now I've seen thouse weights!!

I would think you could get away with 22 gauge if going steel.
not certain though.
Dale

I think you can get away with the 22ga. In fact, that is what I would suggest using. I'm no metalsmith, but it seems like it would be difficult to weld without warping.

We are talking spot welds here (seen an attachment on Frost's website that goes onto an ARC welder).

I don't see heat warpage being a problem.

When riveting, first the chassis is painted, then the panels riveted on. Now when spot welding, it gets painted afterwards. Depending where you live I think there could be a problem with corrosion, between the spot welded panels. There's no way there'll be good paint coverage between the panels, a place already inviting and holding water.


[Edited on 1/26/05 by kb58]

If its a cost issue of steel over alloy, then the steel could still be riveted/screwed / bonded as the alloy is. I think myself I may try and make fiberglass sides-- any idea on the weight difference there.
I would prefer to try and keep the weight down as much as possible as my build is quite abit bigger than most as its a thirties replica with 108 inch wheelbase- aka 1938 tipo lemons racer- and have used a rather heavy 4 cyl turbo.
With no bodywork/seats/fueltank or windshield, rad and intercooler I am already at 1250lbs and would like to keep it to a max of 1500. Power to weight should still be good with 2-300 hp
Dale

Fibreglass is 1.5 times lighter than aluminium. But obviously you will want to make the panels thicker than the ali ones. Anything up to 2.4mm in fibreglass will be the same weight or less than that of ali. Though i have a feeling that you would make the panels a bit thicker than that.

Some densities for reference:

Ali - 2700kg/m^3
Steel - 7900kg/m^3
Fibreglass - 1800kg/m^3

These are all affected by composition, but are close enough for our calculations.

Cheers,
David

quote:

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Originally posted by kb58
When riveting, first the chassis is painted, then the panels riveted on. Now when spot welding, it gets painted afterwards. Depending where you live I think there could be a problem with corrosion, between the spot welded panels. There's no way there'll be good paint coverage between the panels, a place already inviting and holding water.

[Edited on 1/26/05 by kb58]

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You can spray the chassis with weld through primer before spotting it.

I still think that there is a danger of distortion though, and if it did distort it would a) be a bugger to remove it or b) look awfull when painted.

Single sided spot welders are never that brilliant, certainly not from a stuctural point of view. The focus of the heat is not good, and you cannot generate enough pressure to form a decent nugget.

Try out a bit of scrap first before you commit - sorry for being a bit negative, but better that than you being disappointed with the results after a load of effort

I am glad for the 'negativity' as it's what I call reality!!!

I know what you are saying about the moisture and I hadn't thought of that!! BUGGER!!!

As far as strength is concerned I'm more bothered about the look of it all afterwards the strength would be a boon or bugger accordingly.

Why not just rivet on 3mm alloy --- that will increase the strength.
The problem with welding sheet steel on is it will distort just look at the plating on the hull of destroyer -- its caused by the heat expansion of the steel together with phase changes in the crystaline structure it can't be avoided the best you can't hope by careful planning of the welds is minimal disortion but that won't get rid of the lock in stresses just distribute them more equally.



[Edited on 26/1/05 by britishtrident]

I am far from convinced that ANY of the panelling contributed to the strength or stiffness, apart from impact resistance

If you use steeel, why use a spot welder.

Drill holes in the panel and plug weld, then grind down to suit.

THE MAIN REASON IS TO NOT HAVE RIVETS!!!

The strength issue is pretty much irrelevant. I just don't want a ton of rivets all over the car. I may try the plug welding.

See your local bodyshop supplier for some structural adhesive, stronger than plugs or spots

As some have found, be aware some structural adhesives dissolve in certain fluids, like brake fluid! Once that starts, especially at a corner, the strength all goes away. If you do the adhesive, at least rivet the corners.

Was is PBura who used some special tape by 3M to attach the floor? Think that was quite effective. He used some rivets aswell in areas where he thought forces might be greater but that's all.

Chunkielad,
send PBura a u2u about it.

HTH,
James

If your aversion to rivets is purely aesthetic in that you don't want to see them after painting why not fold the panels over the chassis members and rivet them on the inside?

With the exception of the floor I can't think of any area where you need to see rivets, (externally).

I'm not that convinced that thin steel panels welded will contribute any significant degree of rigidity over alloy ones rivetted. But that's just a gut feeling

Mick

a fully bonded kevlar floor would tho

kevlar has a density of 1.4, aluminum 2.7, steel 8 (all figures aprox). GRP - it depends.

two layers of 600g woven roving plus one of 300g CSM should weigh 2.6 kg/ms + gelcoat if rolled properly, and is quite strong enough. for a body pannel.

3 layers of 185g kevlar should do nicely (though I have never tried it) and will weigh maybe 2 ish kg/m

Kevlar is lighter than carbon fibre and is cheaper and represents the best kind of panneling if you can work it.

watch this space .

I have experience of kevlar used in both structural and cosmetic applications. I would agree that it is a viable, (though probably rather expensive) option for panels. I would not consider it suitable for flooring in its basic laid up form with no other form of protection.

Mick

quote:

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Originally posted by Volvorsport
a fully bonded kevlar floor would tho

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quote:

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Kevlar is lighter than carbon fibre and is cheaper and represents the best kind of panneling if you can work it.

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a GRP bonded marine ply floor would be like having a garage roof underneath ya - sry - i used to GRP roofing .

It would in essence lead us to marcos chassis .

i think using coremat and some good decking paint(polyurethane) would leave a strong and durable enough finish for most of us .

I think I'll just use Ally and rivet it!!!!

Sorry to start this guys

I'll double fold into the chassis and fix internally.

Interior panels (OMG did I just say that) will cover them!

Then plan ahead that you have enough room for the rivet tool. It's all too easy to drill holes in a corner where it's impossible to get the head of the riveter into...

Good point mate

Has anyone ever considered using polycarbonate (lexan) as panelling on their car? I was planning on building my bonnet out of it, but then thought about panelling the rest of the car in it. It's damn near unbreakable and certainly won't show up any dents like the ali would. And it's lighter (particularly the 1.5mm stuff)
One drawback is you need a brake press to fold the stuff, but once you rivet it on it won't go anywhere.
So you can have a totally clear side panelling if you don't feel like painting it.

1. It's rather soft. 1.5mm would be like a piece of cardboard in rigidity. It won't stiffen the chassis any.

2. It is very temperature sensitive. I have a Lexan interior bulkhead window between me and the engine. Assuming worst case, from freezing to 150deg F or so, the 48" window widtd will change length by 1/4", or about 6mm!!! How will your rivets deal with that.

3. It'll get scratched up easily.

4. It's expensive.

Sorry to rain on your parade, but it's an expensive way to go that you'll probably not be happy with.


[Edited on 1/28/05 by kb58]

Maybe welding thin panels is now possible without warpage

Metal Cooler

You don't get that much spread with mig anyway. If you button weld through 8mm holes you should be able to avoid distortion if your sheet is well clamped.

I have a low powered Arc welder (the mig I got died and had to go back)

It'll work to 80 amps and 5mm steel (more than enough for any part of the car) and will go down to 1.5mm (or so it says)

You don't need hi power to weld sheet, just the opposite in fact. You want to put the minimum amount of heat into the sheet to avoid warpage.

How about brazing the panels on? The appeal is that it's less heat, plus the brazing would flow between the panels making them extremely strong, far stronger then welding because of the larger surface area. It also solves the corrosion issue, since the space between the sheets is brazed, it won't rust.

I saw a Lotus 340R (the totally stripped back Elise) which had a polycarbonate body. It was quite thick but teh weight saving it had over the usual fibreglass body was amazing. See more about it here

Braising - now there's an idea!!

I will have to get the gear for it though unless I can find someone local.

Watch this space it may just be the way to go!!!

I hope someone who's done it can chime in. My only concern is that brazing an entire sheet onto the car is going to make that portion of the car expand quite a bit. When it all cools down I'm not sure what will happen. Worst case it might end up with ripples. Has anyone tried this?

[Edited on 1/28/05 by kb58]

I would not be too worried about warping the sheet but I think it would cause some warping of the chassis.
Dale

To braze effectively, you need to get both pieces to an equal temperature. You would need to throw a great deal of heat into the chassis, and very little into the sheet. Brazing heat is cooler, but is spread over a much learger area so the distortion in the sheet would be epic, but you could use you sexy ahotalene to shrink it back. Distortion in the chassis would be a different matter, but it may bring the front end down (most home built chassis's have an upward distortion at the front end).

I think I'm gonna start my doing the floor pan with holes and plug welds.

Then, if it works well, I'll do the sides, if not, it won't be too much of a worry for distortion as you won't see it!!!

A tip on the plug welding of your floor pan.
I drilled my floor pan for the plugs and then used an adhesive on the edges of the tubes and clamped in on-- aparently not quite tight enough and to top it off----some of the adhesive ouzed into the holes to make welding a pain in the ass. to put it as politely as possible.
I ended up stitch welding the inside edges of the tubes from inside the car as well just for my piece of mind for safety.
I would not use the adhesive if i did it again-- I would use a sealer on the edges after all welding was done.
Dale

Yes mate thanks for that - I was planning on doing a plug weld and sealer anyway if I go that route as it'll make sure that the space between the panel and the frame has less chance of rusting.

Then on the outside, considered a long weld where the body panel and floorpan meet then a tidy up with a grinder and file should make a nice neat job. If the heat doesn't cause any warpage, it'll look great and would maybe even turn the space frame into a semi monocoque.