Hi,
I know this has been asked before but going back through the forum posts there are a variety of opinions as to whether to weld or rivet and whether to use steel or ally and whether to have a single piece floor or a two piece with a "hatch" in the middle under the propshaft etc etc.

Until I read these posts I was just going to weld my floor using 16swg mild steel and using a three piece design. One large single piece bounded by tubes A1, B1,A2,B2 and then two smaller pieces for the footwell's on either side of where the gearbox sits in the tunnel. I intended to weld in the large squre section first and then overlap the two smaller sections so that the seam will be with the direction of travel and thus shouln't catch on anything or encourage water ingress. The idea of using three sections instead of one large one is due to the fact that I couldn't easily get a sheet of 16swg big enough to do it in one piece (46" wide chassis) and there would be a lot of wastage even if I did.

So....is my plan in line with current thinking or should I consider riveting? I need strength to cope with my RV8 engine so I'm not bothered about a little extra weight. I want to seam weld the outside of the floor at least to prevent water ingress although I may just stitch weld on the inside of the floor. I will of course take precautions to avoid distortion.

I'd appreciate your comments as I am keen to get the floor installed so I can make "vroom vroom" noises...

Cheers,
Craig.

I plug welded (50mm apart) the floor in two sections, leaving room for an inspection/maintenance cover for the propshaft/brake pipes/loom.

I then reinforced this with 13mm ERW in such a way that at no revs would the floor be harmonic - it would be really annoying and probably induce stress cracks. I used 18g steel.

If you weld, you will definately get distortion which you will avoid if you rivet. I have no confidence in rivets in any structural application as if there is any movement, the rivets will loosten and possibly fail. Also alu rivets in steel with road salt and rain is a sure way to end up with you bum on the road.

Oops, forgot the pickie!
Rescued attachment Floor.jpg

On a locost chassis the floor is intended to be a stressed member. Much of the torsional stiffens depends on how well forces are transferred from the frame to the floor (this may not be obvious but is the way things work, OK?). If you weld the floor you don't have to worry about this, it is very hard to mess it up. That's probably why the book say you should use a welded steel floor.
You can rivet a aluminium floor, save allot of weight and still have good torsional stiffens BUT you have to know how to do it properly. What rivets to use, what distant between them, who surfaces should be prepared and so on. If you get this wrong you will have failure and ware because of movement between frame and floor plus a week chassises.

I don't know how to rivet a aluminium floor properly so I'm going to weld a steel floor.

Happy building
leto

people are under the impression that alloy doesent rot away but it does.it doesent rust.alloy up against steel reacts and breaks down even quicker.to get good results with alloy against steel there are certain precautions to take,from my experiance in useing these two together the steel has to be painted and when dry mask off the frame work with duck tape to stop them rubbing together.or use a special type of chromate primer used in the coach building industry and the two parts can be assembled wet or dry,but this is not your everyday primer and trying to find someone who will supply you is another matter.as for the rivets there are some out there that are really good called mono bolts i think they come in 5mm and 6mm but you need a special tool to fire the later ones.the 5mm you can fire with a good set of lazy tongs,as for spaceing them out i would say every few inches ,very time consumeing and expensive

"Solid" Monel structural rivets wont rust, won't react with FE, wont let water etc past, aren't as expensive as stainless, and are v good at the job.
Set them every 50mm/2".

I'd suggest welding in the floor in 18 gauge steel. Some stiffening may be required either longitudinal, as shown above, or lateral by adding a tube across the floor at the front edge of the seats.

16 gauge is a bit heavy for a lowcost floor and though the floor does aid stiffness the actual thickness used seems to make very little difference.

I have heard of riveted floors working loose due to chassis flex on other kits so I'd suggest my high stiffness chassis mods which I've described before and which I've posted a picture of in the photo section.

I suppose all this boils down to either weld in 18 gauge steel or do a decent rivet job on a stiff chassis.

Thanks everyone, I appreciate the advice and most of it agreed with my own feelings to a large extent.

Therefore my car now has a welded 16swg floor. It's only tacked in place on the outside (every 2 inches or so) and I will now stitch weld the inside (1 inch for every 6) before seam welding the outside fully. I know that seam welding is OTT for strength but I am doing it to avoid anything getting into the seam and starting to rust. I will use seam sealer on the inside once all the welding is done. I decided to go for a single floor right across the tunnel as well as I can always cut it back out later if I change my mind. I agree with someone who said that it will be a potential water trap but I'll maybe work around that with some drainage holes. Basically I like the idea of a fully flat underside and the fact that the propshaft and diff and all the pipes which will be in the tunnel are protected. I could have used a removable panel and may still do that but hopefully it's not necessary.

Cymtriks, I agree that 16swg is probably not much better than 18swg but it is what I had already bought for the job some time ago when I got the rest of my steel. I have started to add triangulation tubes (TR5 and 6 so far) and will take account of much of what you have said already on the subject of chassis stiffening.

Thanks again to all who have contributed here.
Craig.

By the way, Mark, I like your skids on the floor and may well copy the idea if you don't mind.

You say your plug welded your floor. How have you sealed the seam? Have you just used seam sealer on the inside or have you used something on the outside too? That's the only reason I have decided to seam weld mine.

Cheers,
Craig.

Syd Bridge:

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I don't know if I'm missing something,

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Hope you're getting well Rorty ol' fella..

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..I'll be seeing you soon!

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..I like your skids on the floor and may well copy the idea..

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I am wondering if anyone on the forum has used the VHB 3M epoxy tape in lieu of welding or rivets. IMO the 1" wide tape should be a very efficient method of bonding the panels to the frame. The bond is supposedly extremely strong and can be used in structural applications.... It also provides a watertight seal if used in continuous perimeter and to top it off creates a boundary layer between dissimilar metals.

I am this >|< close to using the VHB with 14ga ali panels... or should I do 18ga steel with stitch welds... Opinions on that?

I like those skids too. Very cool.

Graber

quote:

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Originally posted by cymtriks
...............
I suppose all this boils down to either weld in 18 gauge steel or do a decent rivet job on a stiff chassis.

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The essential when using rivets in this situation is to coat them with a good jointing compound before reactioning them. his compound should also be spread on mating surfaces of the sheet and chassis, this all aids to prevet dissimilair metal corrosion.

as a general rule in the aircraft industry, for a structurally loaded component, we would be looking for a spacing of about 5d where d=the diameter of the rivet head. Also you should look to have a minimum of 1.5d 'land' which is the distance from the rivet head to the edge of the sheet metal.
I know this isn't always going to be possible on a lowcost chassis though.

The rivets mentioned are called 'Mono Bolt Concept' or MBC rivets and are a far superior rivet to monel 'pop' type. they do require a special head for the rivet gun however. They are available in a huge range of sizes and grip ranges and can even be obtained in stainless steel (although these are incredibly hard to work)

All rivets will fret, the key to a good rivet is to ensure that the hole is clean
,deburred thoroughly, tight, and perfectly aligned. it is a very good idea to get hold of some shett metal grips which are small thumbscrew like devices that can be placed through the rivet holes to locate the material in plce whilst you continue drilling. also use the grips to hold the sheet metal down tight to the frame either side of the rivet you are reactioning.

I know this is makes the job very long winded but it is the only way to achieve a really good joint.


HTH

[Edited on 21/7/03 by protofj]

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Originally posted by Syd Bridge
...See you soon----not metaphoric, got a cousin in the local constabulary claims he lives not a mile from you. I'll be 'round with a six pack(or 2) of genuine xxxx.!

[Edited on 21/7/03 by Syd Bridge]

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Craig,

"By the way, Mark, I like your skids on the floor and may well copy the idea if you don't mind. "

Honoured! The skids add a little strength, hold solid any distortion and will protect the floor if I hit the top odd traffic humps (main reason), they are alternatly stitched evey 3" and can be easily ground off if required and replaced if I crush one or all of them.

The floor. I put a small bead of 3M Structural adhesive on both the inner and outer edge of the chassis and clamped the steel to the chassis. I then cut 8mm holes in the steel with a spot drill and when the adhesive had cured, I plug welded the holes. Some of the adhesive burned where it was close to the plug weld, but most is in place and squidged out to form a watertight seal both inside and out. I sprayed weld thru primer on both surfaces before bonding to minimise corrosion.

Mark,
Sounds like you have covered all the bases then eh?

I wish I had discovered weld through primer before I fitted my floor but I did thoroughly clean all of the steel before assembly so hopefully as long as I get a good continuous seam weld on the outside and a nice seal with the seam sealer on the inside it should be okay. I now have weld through primer which I got from Halfords so I can use it for the remaining panels. At the end of the day it's not going to be all that much hassle to replace a flat floor on a Locost even if I do have it long enough to rust.

Do you intend to drill some drainage holes in the floor? I though it might be a good idea to have two or three large holes with grommets installed for those days when the weather is very unkind. There were a few very nasty showers of rain today which made me wonder what would have happened if I'd been in the Locost with no cover!

Cheers,
Craig.

I think I will leave drainage holes until I feel the need for them. I will have a tonneau cover and when in motion I intend driving that fast that the rain will eventualy come to earth in another county

Syd Bridge:

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Rorty...See you soon----not metaphoric, got a cousin in the local constabulary claims he lives not a mile or two from you.

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Just to clarify the "solid" blind rivets issue, I believe that some are guaranteed to retain part of the breakstem within the rivet body. Without this, the rivet is a hollow tube and doesn't perform too well when there is a shear loading between the joined components. With the breakstem retained, the rivet essentially becomes solid and its shear performance increases massively. This is particularly true of aluminium rivets which are fairly soft; the steel breakstem adds a great deal of shear strength.

FWIW, I used 4mm sealed-end aluminium rivets which retained a portion of their breakstem (or mandrel if you prefer) to retain my 2mm aluminium floor, spaced at 25mm intervals. Clecos were used while the holes were being drilled to stop panel creep, then the floor was removed and all the holes deburred, then a bonding & sealing compound was applied before rivetting. Pic here.

Cheers,

Eddy

Sounds just about perfect.
did you consider riveting to cross members as well as around the edge ?

The weight benefit of a aluminium floor is big and I would like to be able to consider it an alternative. The only way to get there is to understand how a riveted bond is supposed to work in this application. So please excuse a very theoretical question.

Is the rivet supposed to transfer any sheer loads at all, in theory?

Leif

Structural rivets are designed to carry sheer loads. Generally this is the kind of load they handle best. Using them in tension for highly stressed joints is not a good idea.

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Originally posted by leto
The weight benefit of a aluminium floor is big

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A 4' by 12' sheet of 0.063" ali weights about 42.5 lbs (19kg)

The same size and gauge steel about 125 lbs (57kg)

0.050" steel same size weighs about 102lbs (46.5kg)

[Edited on 23/7/03 by ProjectLMP]

eddymcclements, your description is more eloquent than mine, and is what I was getting at.
I've just been looking at my 2003 Gesipa catalogue (Gesipa Blind Riveting Systems Ltd, Keighley, W. Yorks. Tel: 01535 212200), and they make "Bulb-tite" rivets with "superior clamping power", which are "perfect for securing difficult or dissimilar materials."
They also do all the regular stuff, including the rivets I was alluding to; the "high clamp up, high strength, weather tight, flush break mandrel, hole filling, dual lock design, structural G-Lock and MegaGrip rivets"
Don't believe me? Give them a call!

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Originally posted by craig1410

Leif, The weight benefit is not that big IMO............

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Leif,
However, using projectLMP's figures, a 12 square foot section(roughly what I needed for my floor) of 16swg Ally is about 4.8 KG and in 18swg steel it is 11.6Kg. This is only a saving of 6.8Kg's and doesn't take account of all the extra structural braces you would need to add to the chassis to replace the strength taken away by using the aluminium and all the rivets which if of the solid type surely must add up to 0.5 to 1Kg on their own. So I reckon that you will only save maybe 4 or 5 KG's not the 10 to 15Kg's that I originally thought might be possible.

In my humble opinion unless you are building a car purely for competition and probably using aluminium for the spaceframe as well, it is just not worth the hassle to use aluminium for the floor. You could easily save 6.8 Kg's elsewhere on the chassis and give greater benefit to the overall design than on an Ally floor.

Using alloy uprights for example or using magnesium wheels. This would cut unsprung weight and give a potentially greater weight saving. You could reduce the fuel tank size or use lightweight seats or throw out the carpets or lose the radio cassette etc etc.

I appreciate and respect everyone's opinion's completely but for me there is no need for an aluminium floor in a Locost. There....said it, it's official !

Cheers guys,
Craig.

Of course, ignoring the Locost idiom totally, a honeycomb (aluminum, nomex or somesuch (balsa! )) would give superb stiffness and have a lighter strength to weight ratio.

It'd have to be bonded though, but that would remove any worry about rivets!

Anyone got any stiffness/weight figures to hand?

ATB

Neil.

Personally, if I were to use aluminium instead of steel, I would feel obliged to go for a thicker section to protect against penetration by rocks, etc.

I'd probably use 3mm ali instead of 1.6mm steel.

This means that the weight difference would not be so great.

Just my 2p!

David

[Edited on 24/7/03 by David Jenkins]

Noodle : I think you might be suprised how little difference expensive honeycomb composites make in this application. Cymtriks fairly recently posted a site of someone who had modified an ultima chassis to make it stiffer and measured the effect of each one, and while some modifications where extremely effective, putting in an expensive floor, while looking very good made no noticeable difference to the stiffness of the chassis!

This isn't exactly comparing like with like, but it does give some indication.

Kingr

Craig,
thanks for the calculations. With good numbers it's lots easier to make good decisions.
I think you are right there. There is no point to put down that much work and money to save that little. I'm not very keen on stressed alloy skins anyway, as they generally fatigue more easily than steel.
Alloy uprights and magnesium wheels is somewhat to the "hicost" side, think I'll stick to saving weight on the driver.


BTW I 'm a little bothered by the lack of "good numbers" in this discussion. Protofj have shared some thumb rules, (thank you protofj, very useful ) but that's about it. Anyone out there how have any calculations on aluminium gauge, rivet size, rivet c/c, number of rivets or something like that, for a locost floor?

Cheers Leif

Thanks Kingr,

I suppose it's the law of diminishing returns. If the chassis's already stiff and suitably fit-for-purpose it won't make much difference, good-looking or not.

Has anyone got a CAD modelled chassis that could show how this could affect the Locost?

ATB,

Neil.

With not so much of a weight penalty for steel, I am considering using 18 ga. steel for the area behind the seats as well.

This would have to help stiffness somewhat, and would get me down to no rivets to speak of (plan to use 3M VHB tape for most ally panels).

Pete B.

We have a CAD-modeled chassis, but just for dimensions and fit, not stress analysis. It's more or less a mcsorley 7+4, but we're fooling around with it a bit.

Has anyone calculated the weight penalty of using all 18gage or using 20gage one the side and back pannels instead of alloy.
Dale

Dale, couldnt give you accurate figures for replacing panels with steel, but for ease of working aluminium is probably more suitable for these panels. Ali bends far easier (quite important especially iwth the back panel), and the temptation with steel is to weld to chassis. This will give ultimate strength, but can mean that the panels are at risk of heat distorting, which will be virtually impossible to remove.

HTH Stu (From the aluminium floor and panel camp)

I agree with Stu16v on this one. I'm all for a steel floor as you will know already but for exterior body panels I think that Aluminium is the way to go for both ease of working and corrosion resistance. However, I will be looking at this magical 3M tape for bonding it rather than messing about with loads of rivet's. The body panels aren't structural as far as I can see and thus are just for aesthetic value. I may look at using fibreglass as an alternative too.

My opinion is to use steel for the floor and behind the seats but to use Aluminium for the cosmetic panels.

HTH,
Craig.

[Edited on 25/7/2003 by craig1410]

has anyone considered attatching a thicker piece of alloy bar on the attatchment points and tapping it so it can be bolted to the steel frame- the alloy bar and sheet could be welded to each other then bolted on????
Dale

Dale,
If I'm understanding you correctly then the only disadvantage I can think of is the need to weld in crush tubes into the steel frame everywhere that a mounting bolt would be going. I'm sure you are aware that you can't just drill a hole through a tubular member and then put a bolt through it so maybe you are meaning something else. For example, having small mounting brackets welded to the inside edge of the lower chassis rails to take little set screws.

You could potentially use rivnut's attached to the lower chassis rails as these don't require crush tubes. You could then use a slightly thicker ally sheet for the floor (or the flat bar you were talking about here) and using countersunk set screws you could mount the floor.

In any event, I stand by my own statement that aluminium isn't justified for a Locost in all except the purest competition purposes where ANY extra weight is to be avoided at all costs.

Cheers,
Craig.

Welding thick alloy to light sheet will be virtualy impossible without a lot of distortion.
IMO its best (and simplest) to rivet the panels straight to the frame, sealed and bonded to boot with a decent sealer/adhesive. If you dont like the rivets showing, wrap the ali round the chassis members.

HTH Stu.

I welded my mild steel floor all the way round the edge, I wanted it water proof!!!!!, There was some distortion but not toooooo bad.

see car at: http://www.groovy42.freeserve.co.uk

[Edited on 30/7/03 by Surrey Dave]

That's my theory too, keep the water out (or is it keep the water in...)
More importantly is to keep the water and salt etc out of the seam between chassis and floor or it will rot big time. I intend to seam weld the outer seam only once I have stitch welded the inner seam (1inch weld, 5inch gap). That should hold everything in place and minimise the amount of heat that I'm putting in to the metal. Even when I seam weld the underside I will do it alternately on each side and only do 3 inches at a time before moving elsewhere. At the end of the day who cares about a little bit of distortion as it's under the car anyway.

Cheers,
Craig.

As long as the floor is diagonally braced, even with the smaller diameter 1" pipes that are used along the engine bay, the need for any structurally supporting floor panel is minimal.
I agree that 18swg be better all around than 16 (one could probably even get away with 20swg with Mark's ribs). The transmission tunnel is a much higher concern for me, and I will most certianly weld 16swg plates along the cabin side of the tunnel to double as structural support and shatter guard for the driveshaft and transmission (i don't want to be sorry that I chose a 300+hp motor). In order to get an idea how the stress transmission behaves, build some balsa wood models of the transmission tunnel and side walls and a floor - I know it's not really fair to transcend materials like that, but the underlying structural ideas carry over from metal to wood - the tunnel and side walls direct much more of the torsional force through the frame than the floor alone. IMO, if you're going to use heavy pieces, use them here where they will protect you!

I plan to diagonally brace my floor and lay a fiberglass "tub" along the exterior of the frame for the floor. This tub will extend up along the sides, as well as over the front and rear bulkheads. Given that I can make this tub continuous and enveloping to some of the key frame members, it will most likely add more structural support than a simple panel of metal. My car will also be closed in from the weather, so I won't have to worry about rain accumulating on the inside. I will have a gap in the fiberglass to span the underside of the transmission tunnel, where I will mount a removable panel that is to be raised from the level of the rest of the floor. This panel is mainly to direct air out from under the car in an effort to generate downforce. Downforce, I imagine, is somewhat of a silly thing to worry about woth Locosts, whereas I'm building a full-bodied car complete with downforce-inducing panels and planes...

Anyway, I totally agree that the messing around with aluminum is probably not worth the weight savings (except for extreme applications). One thing that is important to me is to have faith in your engineering: piece of mind is always more important in my book. I am not one to quickly dismiss saving 10 or 15kg (20 lbs for me ), but I would rather buy a lightweight Kirkey racing seat in leu of a fully upolstered job and be less one gallon of fuel capacity than wonder if the seal between my floor and frame is going to hold up...

Besides, my girlfriend only weighs 100lbs (45kg)

Hope this helps, and let me know if I'm too much of a loon

-MR

quote:

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Originally posted by ProjectLMP
A 4' by 12' sheet of 0.063" ali weights about 42.5 lbs (19kg)

The same size and gauge steel about 125 lbs (57kg)

0.050" steel same size weighs about 102lbs (46.5kg)

[Edited on 23/7/03 by ProjectLMP]

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By the way, I've posted a thread about Carbon Fiber (due to it's availibility on Ebay) in the LOCOST RELATED section. I've thought about using Carbon cloth for body panels, but could it also be used for frame re-enforcement as well? Maybe a Carbon floor panel?

If anyone knows anything about it (of which I know little) please do comment...

Thanks
-MR

mranlet,
Yes I pointed this out on page 3 of the thread and in fact my estimate put the difference at 6.8 KG's due to only needing about 12 sq ft of steel/ally for the floor. I am gauging this by the fact that I bought a 6ft x 3 ft sheet and still have between 4 and 6 sq ft left. I also pointed out that this doesn't take account of the weight of all the rivet's and extra structural braces which may be required with aluminium which aren't needed with steel. Yes the steel welds will weight a little bit but not much if done correctly.

One advantage of Aluminium which I don't think has been mentioned is that it should be quieter and less likely to "drum" like steel but as Mark pointed out you can achieve this effect with steel by using some 13mm ERW up the underside.

Cheers,
Craig.

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Originally posted by leto
On a locost chassis the floor is intended to be a stressed member. Much of the torsional stiffens depends on how well forces are transferred from the frame to the floor ...
leto

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it has been mentioned in a thread called 'subject: floor rivet requirements' or something along those lines. if you search for honeycomb it comes up in a fairly short list.

it was mentioned that it is prone to puncture and delamination.

all hearsay as i dont even know what it is!

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Originally posted by jcduroc
Has anyone considered using aluminium honeycomb plate to make the floor? (My LHS brain cell just popped this idea!...)
If doing so how would you "connect" it to the frame?

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Originally posted by mrantlet: My car will also be closed in from the weather, so I won't have to worry about rain accumulating on the inside

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Besides, my girlfriend only weighs 100lbs (45kg)

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18g steel,and I plan on using a bead roller
inbetween frame members w/the beads running laterally,for added rigitity.

No, I dont own a bead roller but I did talk my employer into buying one for a job we did...and plan on bead rolling my floors after hours under cover of darkness..

Oh, single piece.

Fletch

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No, I dont own a bead roller but I did talk my employer into buying one for a job we did...and plan on bead rolling my floors after hours under cover of darkness..

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20swg aluminium sheet,1 on bottom of chassis rails 1 on top of chassis rails, VHB taped onto chassis, then injected with polyurethane foam to add rigidity and turn floor into a stressed member. Would also help with noise reduction

Can also be used for side panels.

I used a one piece section of 18ga galvanized steel, glued with urethane adhesive and riveted every 3" or so along every lower tube.

In a test with glue alone, I had to nearly bend the steel sheet to destruction to remove it from the tubing. With the addition of a few rivets, its going nowhere and has the advantage of being sealed at the same time.

quote:

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Originally posted by Dunc
20swg aluminium sheet,1 on bottom of chassis rails 1 on top of chassis rails, VHB taped onto chassis, then injected with polyurethane foam to add rigidity and turn floor into a stressed member. Would also help with noise reduction
Can also be used for side panels.

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Did he veto the English Wheel, guillotine and sheet metal brake, or have you not asked him yet?