I'm a bit worried about rust. My BMX bit the dust because of rust when I was six and I spent a lot of time underneath a 15 year old citroen at 17 getting rid of the stuff too, so having decided to build this thing i'm keen on it lasting forever (or until i break it). My main concern surrounds the amount of holes in the chassis due to riveting and the amount of water these are going to let in once the flexing of the car causes the rivets to loosen and settle. Anyone share this concern? My original plan was be generous with the silicone, make sure everythings airtight and chuck some desicant inside the tubes wherever possible.
THere is of course the stainless alternative, which I know has been done before, and it does seem attractive to me but I'm concerned there may be pitfalls I haven't thought of.
I've never welded stainless (or worked it as far as i can remember) though i have reasonable skills with mild. I gather that welding stainless is trickier and you need the slightly more expensive argon gas for mig, but it's not too tricky a learning curve (like welding Al/Ti would be)- any thoughts on this?
Strength-wise I'm told the more common stainless alloys are slightly stiffer and stronger than mild, but I'm not sure about fatigue, general durability or weld strength. What are your thoughts folks?

You could make the chassis in mild and have it galvanised all the holes for rivets etc would be ideal for getting good coverage.

I had thought about that breifly, but I had dismissed it as I had assumed it would be pretty expensive and i didn't know if you could find someone who could do something that size. Have you had it done, or know someone who has? Would be a good solution.

Oh dear traumatized from the age of six because of a rusty BMX, how tragic.

If I was going to make a new chassis, you never know…I have some plans. I would also do it out of stainless. I think cutting the tube with a hacksaw might be out of the question and jig saw blades get really hot and don’t last long trying to cut the stuff. Then again there’s little sheet metal on the chassis now that their making the floor out of ally. I’ve just never noticed any difference welding stainless. Things like the seatbelt anchorages with their special thread might prove difficult to obtain in stainless. Would be a shame to panel over it, what about clear side body work?

[Edited on 3/1/07 by macnab]

Cost isn't the issue with galvanizing as it not really very expensive. The real problem is having to drill loads of holes all over the place to let the air escape from all the tubes due to the risk of explosion from pressurized air. Just imagine that happening in a pool of molten metal

It is also quite heavy as it coats both the outside and inside. …

[Edited on 3/1/07 by macnab]

I loved that BMX. The pain dulls with time, but it will always be there.

Interesting about the welding, i was kind of hoping that would be the case. Will be months until i can get the steel anyway so I'm going to get some practise in.

the state my bikes were in from throwing them over fences and jumps not to mention the odd crash, rust was the least of my worrys...

Have a word with Paul - 907 - he is the Stainless welding guru!

I may be wrong but I think Paul G (907) built his using stainless, he would be the man to ask for welding info.
Cheers
Alex

Bugger, Dave beat me to it

[Edited on 3/1/07 by ecosse]

Although with an avatar like that I am not going to complain

[Edited on 3/1/07 by ecosse]

Cheers folks, all very useful stuff! Think that's probably my mind made up, looks a good route. Will get practising welding with the cutlery.

I would be careful about stainless because it can become brittle I think - but then I'm not a materials engineer.

Make sure you get the right grade of stainless for the chassis as each grade has very different mechanical properties.

And no I don't know what grade to go for.

Another alternative would be to make the chassis in mild steel and then have it zinc plated and silver or yellow passivated. This process gives a much thinner coating than hot dip galvanising. The plating could then be left as the final finish, or painted in the normal way to provide extra protection. What I am not sure of is whether plating tanks come in sizes large enough for a chassis.


Mal

Talk to Paul, (907) not only is he a Stainless Steel Welding Wizard, he know his onions as well. (Its his job)

If you make it from ordinary steel... then a hole in each end of the tube and spray in Finnegans Waxoyl with an Air line driven Wax gun (Not a Schultz Gun) with long nozzles / pipes.

OK Its messy, and it will seep out on very hot days... but it wont rust. I use this on my Land Rovers, and they see far more water (Imersed in the stuff in Rivers etc)and mud.
We cut Waxoyl with about 10-15% White spirit, and warm it up as well. (NO Naked flames for heating!!)

Cutting it with a thinning agent, allows it to run into all the nooks and crannies.
This is a successful method, albeit a bit messy.

Put a BIG dust sheet on your concrete and sit the car on the sheet. Allow it to drip for a few days, put plastic plugs / bungs in the holes. Dispose of sheet when finished.

Just my 2d worth.

I started my chassis a year or so ago (before starting to rebuild my house). I am now back on track having just finished the house, anyway the point is I am using stainless for my chassis. The cost when I bought the material was about £130, but the price has gone up considerably since then.

I use a TIG welder rather than MIG, It is pretty easy to master and it is just like hot soldering really. The main thing to watch out for is that stainless expands (and contracts) much more than mild/carbon steel with heat so keep checking angles etc when tacking up as things can deflect incredibly.

Hope this helps

G

Personally I dont think rust is really worth worrying about. My mate recently restored an old pre-lit westfield - about '88 i think so getting on for 20 years old. It had been dumped in a barn for god knows how long, red GRP gone brown, ally panels horrible etc etc. But the powder coated chassis was in perfect condition - no rust anywhere.

These cars dont see much use, and that's normally in good weather. It's much harder for water to get in a 7 chassis (close to impossible, especially if you use sealant and/or closed rivets) than to, say, get inside parts of production cars.

I've never known of a seven owner complaining about a rusty chassis. Even in a classic restoration the chassis wont normally be suffering from rust. There's also the current price of stainless that may be worth considering! And finally there's the fact that once you start in this hobby you'll be thinking about the next car before the first is finished . I doubt anybody owns these cars for very long - even a scratch built pride and joy.

Just my 2p.

Liam

quote:

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Originally posted by Liam
Personally I dont think rust is really worth worrying about.

There's also the current price of stainless that may be worth considering! .

Just my 2p.

Liam

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Thanks fellas. Lot of information one way and the other... About the brittleness, that did worry me a little as I've heard similar. I will check up on exactly the alloy i need before buying anything.
On the other hand, I do buy into the galvanising arument, and I've used waxoyl myself to good effect, although it is bloody foul stuff and your car smells like formaldehyde forever.
Looks like both routes are good choices. I think i'm still leaning toward stainless though, partly because of the longevity and partly because of the lack of paint requirement, but boulstered by the comments people have made about welding the stuff. I do know what you mean also about planning the next project before the paint's dry on this one, but i already have projects planned to retirement anyway (i'm 28) and this may be the only car. It's with that in mind, and the possibility of picking my grandkids up from school in it some day that I want to do this to last.
Of course, if i do you can garantee we'll be out of oil in ten years anyway. but if worst comes to worst, at least we've all had something to talk about today!

Hi.

Wow. I haven't seen my name in print so many times since...... Mmm, best not go into that. TMI


Loads of good stuff on this thread already so I'll try to keep this short.

Firstly rust. I have a mate with an original 7 that's had a few bits of his chassis replaced due to corrosion.
He has owned the car from nearly new, 1971, so that's 35 years.

Build a stainless car because you want one, not because of rust.

Stainless is prone to cracking, some grades more than others. Avoid 409 like the plague. I've used 304L and 316L.

It's sensible to avoid solid mounted engines and anything with excessive vibes. (vee twins ???)

I have panelled and trimmed mine so that much of the welding is visible so I can keep an eye on it in years to come....

Which leads on nicely to my other advice;

Get a TIG set... Sooooo much nicer.


Expensive? Err, yes. But think of all that money that you'll save on paint.


U2U if you need any info ( or phone or call in if your localish )

All of this is IMHO you understand.

Below is a pic of Test Pilot Ted. Top bear, but a bit on the slow side.


Good Luck

Paul G
Rescued attachment chassis-102-s.jpg

I don't know if I missed it any posts above, but the answer to all the rivet holes is to use closed end rivets. And as few as possible.

There's also talk of silicon sealer. Better to use a top notch polyurethane sealer. Sticks like the proverbial 'shite to a blanket.'

Galvanising. Don't even think about it, anyone!!!! Now I know someone will come back and say 'I've galvanised 1000's of 7 chassis and never had one warp'. But, I've seen two after a dip in the zinc tank. Only good for 'installation art' . I stood beside the tank when a similar fabrication was lowered in. The noises it made as the heat 'stress relieved' the welds were incredible. Creaked and groaned like an arthritic old goat!

Cheers,
Syd.

[Edited on 4/1/07 by Syd Bridge]

Thanks Paul G, your advice is well received. I shall research alloy types and hopefully test a few. I know a chap who's a steel stockholder so hopefully I can get my hands on a few bits and peices to weld then bash about in a pseudo-scientific way.

Couple of queries:
Have you had any issues with galvanic corrosion? Fixings rusting away in no time when in contact with the stainless steel? My gut tells me this wouldn't be an issue in a car but worth asking.
Tig - I'd love to try it, but from what i've seen it seems that to buy one with the flexibility to match mig costs at least a grand (new). Is there a significant difference in the weld strength between welds made with tig and mig in stainless? I've heard opinions either way.
Also, it occured to me that a bit of gussetting on the joins most likely to flex and crack might help. Any thoughts?

just to second Syd on the galv idea, not at all good!!!

it will warp like you would not believe, we did a double deck twin til bed car transporter trailer some years ago and that twisted enough to need "re-tweaking" with a big press when we got it back from the galvanisers.

with regards to stainless chasis...

there is a new material available, called CRW-1000N, which is a Stainless steel but with 980 N/mm2 tensile strength, which is quite a bit greater than 4130, and as much as 15CDV6, which is a current wonder metal for motorsport...

price is, of course, not locost teritory, but might be interesting for all of us thinking about building naked Atom type cars..

Tensile strength isnt important in a chassis, its the stiffness of the material you use and the way you design for the material you use as well taking into account its properties - hence an aluminium chassis will look very different from a steel one and a carbon fibre one etc.. If you design you chassis correctly you never even get close to the yeild point let alone the UTS (which is a made up quantity anyway)

David

Here's a plan - how about using pre galvanised tube and sheet for a build? According to the link below it seems zinc vapourises at a temperature lower than steel's melting point anyway so it need be paid no extra attention whilst welding.
www.sperkoengineering.com/html/articles/WeldingGalvanized.pdf
This is a theory I'd want to test first of course, but worst comes worst you could sand off the zinc layer within 10mil of the weld anyway.
Although this would mean you have exposed parts at the welds, you'd still get cathodic protection so nothing should rust.

Its best to clean off the galvanising first, the fumes arent particularly good for you and it does contaminate the weld.

David

I had a sneaky suspicion that may be the case, thanks for letting me know. Gut feeling was to sand off 10mil near the joint anyway regardless of whatever I'd read, then use spray-on zinc to replace it and paint as usual. Car should then be pretty much imortal! If stainless proves too expensive then this is my route i think.

if I were you, I'd use non zinc plated tube, sand everything after welding and then either powder coat it or use an epoxy etch primer...
if you attach the panels with pop rivets, then just spray some waxoil inside the tubing that you drill and seal the rivets with silicone... that should do it..

Hi JL

quote:

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Originally posted by jlparsons

Tig - I'd love to try it, but from what i've seen it seems that to buy one with the flexibility to match mig costs at least a grand (new).

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quote:

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Originally posted by jlparsons
Thanks Paul G, your advice is well received. I shall research alloy types and hopefully test a few. I know a chap who's a steel stockholder so hopefully I can get my hands on a few bits and peices to weld then bash about in a pseudo-scientific way.

Couple of queries:
Have you had any issues with galvanic corrosion? Fixings rusting away in no time when in contact with the stainless steel? My gut tells me this wouldn't be an issue in a car but worth asking.
Tig - I'd love to try it, but from what i've seen it seems that to buy one with the flexibility to match mig costs at least a grand (new). Is there a significant difference in the weld strength between welds made with tig and mig in stainless? I've heard opinions either way.
Also, it occured to me that a bit of gussetting on the joins most likely to flex and crack might help. Any thoughts?

---

Thanks all, that's given me lots to think on. Your car looks a stunner Paul G, best argument for stainless yet, particularly the cockpit. You do your own nose by the way? What's it made of?
Oh and I'm with you on rivets. Never intended to touch the things myself, even if tapping all them holes is going to be a pain in the rear end. I'm convinced the fit of the panelling will have a big effect on rigidity.

Thanks, but I do only take pics from pleasing angles, and isn't Photoshop wonderful?


Hopefully the body will all ally.

I'm on the last leg, or should that be, I'm on my last legs.

Just the bonnet to finish and the rear arches to make.

It has been a bit of a marathon. O, and did I mention all that polishing.


Paul G

quote:

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Originally posted by 907
Just the bonnet to finish and the rear arches to make.

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Has anyone had welding fume fever or galvyflu as it’s also known.

I have (welding up the buggy), it’s awful, felt like I was dieing.

Do that kind of thing outside, with the wind blowing away from you.

In my old age I don't fancy spending all my spare time polishing the car. My panneling will be light gauge steel fill welded to the chassis with the entire frame/tub painted with Por15 then the tub coated inside and out with a light coat of Linex bed liner which is a fairly light polly and will seal the pannels to the frame.

Hi Gazza,
I know what you mean about the pre-galv tube and having the corners unprotected, but if I used pre-galv I'd still paint it up as if I were using mild. It'd be purely a solution to long term corrosion, so to be honest not all that worthwhile, but if I could get it for very near the price of mild and it made next to no difference in work time then I'd say what the hell and do it. The only bit I'd go out of my way to use galv for would be the floor sheet, which in my experience is the first to go emmental.

It'll peel off in six months unless you treat it first. My mate painted his galvo bike shed with red oxide then paint on top and it all cracked and flaked off. Google it and you'll find solutions to the problem but it's all a bit OTT, you aren't going to drive it in the rain that often and a mild steel chassis with paint will outlast a commercial car body if you keep it under cover. Edit:- Just another point, I've never actually seen pre galvanised RHS for sale anywhere. Trailer chassis and such are all treated after manufacture.

[Edited on 6/1/07 by Peteff]