chunkielad
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| posted on 26/1/05 at 12:21 PM |
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Panels
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?
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SeaBass
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| posted on 26/1/05 at 12:43 PM |
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One question Why? Why do you need to add 'extra rigidity'? Are you using a Merlin engine?
Cheers
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flak monkey
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| posted on 26/1/05 at 12:44 PM |
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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
Sera
http://www.motosera.com
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James
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| posted on 26/1/05 at 01:04 PM |
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quote:
Originally posted by chunkielad
I would like the extra rigidity.
If you want the rigidity then apply Cymtrics' chassis mods- double the chassis rigidity for minimal weight penalty.
Although for that matter I don't know of anyone who's built a standard chassis Locost who's said "Damn this chassis is bad- if
only it'd had more rigidity"!
Cheers,
James
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chunkielad
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| posted on 26/1/05 at 01:06 PM |
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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!!
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Dale
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| posted on 26/1/05 at 01:36 PM |
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I would think you could get away with 22 gauge if going steel.
not certain though.
Dale
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chrisf
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| posted on 26/1/05 at 02:10 PM |
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Yep
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.
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chunkielad
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| posted on 26/1/05 at 02:13 PM |
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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.
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kb58
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| posted on 26/1/05 at 03:25 PM |
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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]
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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Dale
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| posted on 26/1/05 at 03:34 PM |
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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
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flak monkey
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| posted on 26/1/05 at 04:43 PM |
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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
Sera
http://www.motosera.com
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James
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| posted on 26/1/05 at 05:00 PM |
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quote:
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]
I was thinking the same myself actually- there's no way you'd get paint into the microthin gap between the two- but moisture certainly
would get in IMHO.
Sorry to be negative!
Cheers,
James
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MikeRJ
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| posted on 26/1/05 at 05:06 PM |
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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.
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Mark Allanson
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| posted on 26/1/05 at 07:02 PM |
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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
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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chunkielad
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| posted on 26/1/05 at 08:33 PM |
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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.
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britishtrident
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| posted on 26/1/05 at 08:40 PM |
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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]
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Mark Allanson
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| posted on 26/1/05 at 08:44 PM |
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I am far from convinced that ANY of the panelling contributed to the strength or stiffness, apart from impact resistance
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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wilkingj
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| posted on 26/1/05 at 08:59 PM |
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If you use steeel, why use a spot welder.
Drill holes in the panel and plug weld, then grind down to suit.
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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chunkielad
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| posted on 26/1/05 at 10:34 PM |
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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.
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Mark Allanson
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| posted on 26/1/05 at 10:39 PM |
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See your local bodyshop supplier for some structural adhesive, stronger than plugs or spots
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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kb58
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| posted on 27/1/05 at 01:34 AM |
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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.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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James
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| posted on 27/1/05 at 08:22 AM |
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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
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Mix
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| posted on 27/1/05 at 08:56 AM |
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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
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Volvorsport
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| posted on 27/1/05 at 02:44 PM |
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a fully bonded kevlar floor would tho
www.dbsmotorsport.co.uk
getting dirty under a bus
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smart51
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| posted on 27/1/05 at 03:04 PM |
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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.
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