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 Post subject: Stainless frame
PostPosted: Sat Aug 07, 2010 9:56 pm 
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Location: Columbia SC
I did a bunch of calculations and 304 stainless would make a very good frame. Stronger than 1018 by
about %40, NEEDS NO PAINT, doesn't rust, easy to weld(relatively). It's about 3 times the cost of
mild steel, but would save time and the hassle of painting the frame and keeping it rust free.
stronger to boot.

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 Post subject: Re: Stainless frame
PostPosted: Sat Aug 07, 2010 10:35 pm 
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Dr Hess has an SS frame on his locost. He frequents this forum sometimes but is on the Yahoo site a lot. Great guy and very helpful if you have questions. Russ

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 Post subject: Re: Stainless frame
PostPosted: Sun Aug 08, 2010 12:52 am 
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Location: Charlotte, NC
I'm sold. In fact last Fri. I picked up a 90 cf bottle of trimix and 2# of .030" 308l wire. Having worked with 304 & 316 for 30 years, I'm comfortable with it's few peculiarities. It does crawl around more due to greater expansion when welding.

I was quoted $2.43/ft for 1" sq, and $6.19/ft for 2". Sixeen ga. x 4' x 8' was $188.00.

Cheaper than powdercoat. No teardown/paint/reassemble. Can be modified/repaired easily.


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 Post subject: Re: Stainless frame
PostPosted: Sun Aug 08, 2010 1:48 am 
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Yes, stainless moves around a lot more than mild steel. Also, depending what type of stainless it is, it doesindeed rust, as the heat from the welding drives the chromium ouf of the weld area. Just be sure you've done your metalurgical research correctly, as some stainless steels are quite weak in comparison.

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 Post subject: Re: Stainless frame
PostPosted: Sun Aug 08, 2010 5:07 am 
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Posts: 179
bremms,

If I was a wealthy guy with frame building experience I would go with Stainless steel. It's easy to weld with stick rod but you have to do it in steps to keep heat distortion down. Then you can tig weld it if you have the equipment handy and know how to weld with tig. Then wire feed weld it. The way I see it a reagular ole mild steel frame is going to last three lifetimes if not driven in salty conditions anyway. I'm building my first frame in mild steel but if a second frame is gonna be built, I plan to do it in stainless. Right now I'm saving and liquidating assets to build a house and a shop. I plan for this home and shop to be my retirement place so small projects are on the low end of my list. When I get my what seems like fifty or so onging projects sold off or disbanded I can and will concenrtrate on the one locost project. In the future with luck I'll have a shop with enough space and equipment to do anything with a Lotus Seven inspired car. We are all at different points in our lives and abilities. If you have the know-how, funds and the tools to do a stainless frame I would say YES! Definately build a stainless frame but be a true craftsman, get help form or hire a true craftsman to weld it together. Stainless is definately one of the better longer lasting materials to work with and build with. "Do it once, Do it right." Is what Paw Paw used to tell me.



Mark.


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 Post subject: Re: Stainless frame
PostPosted: Sun Aug 08, 2010 2:07 pm 
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Location: The Humid State of North Carolina
KB58 wrote:
depending what type of stainless it is, it does indeed rust, as the heat from the welding drives the chromium out of the weld area. Just be sure you've done your metallurgical research correctly, as some stainless steels are quite weak in comparison.
I have to agree here, but include that no matter what grade of stainless, it can rust, even without being welded on. I would worry about the possible "false" sense of security that the use of stainless might give someone not knowledgeable with it's unique properties. Now instead of inspecting religiously, or being able to see flaking paint or rust streaks as an indicator, the initial notification of failure might be catastrophic!

I work in the Food Service Repair industry and have seen even the best stainless (i.e. 400 series) rust when exposed to the right environment. I have seen stainless rot away just like steel when exposed to salts and damp environments. Same that you might find on roads. Even driving on roads that have been salted in the past, and then storing it away, environmental changes can produce moisture, combined with lack of air movement and you have the perfect environment for damage to stainless metals.

Stainless would give you a strong frame, if like KB58 stated, you use the right ones (I've shattered tons of 304 knife blades!!). It would give you a basically maintenance free frame, but you would still have to disassemble it and inspect it more closely as you wouldn't get the indicators you might see with a mild steel frame.

How do you intend to mount panels to the frame? Stainless is only so because of the collection of a passive film of chromium molecules (yes, only a few atoms thick) on the surface, so when you punch a hole into it to mount panels, you'll disrupt this layer and cause what you intended to avoid. Yes, the chromium does resurface when scratched or damaged, but with two surfaces constantly rubbing together, especially if a dissimilar metal (rivet/hole, panel/frame...), you'll loose the "stainless" property and be in the same mess as everyone else, but with a really pretty frame.

Also as Gyrofli stated.. a normal mild steel frame would last several Locost lifetimes, so does the added expense, necessary inspection and other requirements make it a better way to go? I would love to make a SS frame, but only if I was doing it for a reason (i.e. theme of the car). It welds like butter and would be pretty, but after having see some of the shiny all alum cars, I'd probably pass, as being blinded by random sun flares isn't my cup of tea.

Interested in seeing the pics when you get it going though. Gonna be pretty!

KS

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 Post subject: Re: Stainless frame
PostPosted: Sun Aug 08, 2010 2:56 pm 
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Location: The Humid State of North Carolina
bremms wrote:
I did a bunch of calculations and 304 stainless would make a very good frame. Stronger than 1018 by
about %40, NEEDS NO PAINT, doesn't rust, easy to weld(relatively). It's about 3 times the cost of
mild steel, but would save time and the hassle of painting the frame and keeping it rust free.
stronger to boot.
The other thought that I have to use and always keeps me grounded is that: If it's such a good idea, why don't others do it?

Not that a SS frame is a bad idea, but if it was a better alternative to other materials, why doesn't everyone do it?

Why aren't all race cars built from it, because typically theirs is a cost-not-an-obstacle mentality, right? One racer did many years ago.. here, but he was the lone exception I found rather than the rule. Another example with it as a monocoque chassis is found here.

Why don't home-built experimental aircraft use it? Weight is within oz of each other, with SS actually being lighter. They have to have inspections for corrosion and cracks, so why don't they use it when it would eliminate half of their issues?

We're not the first horses to join the rodeo, nor are we the most critical need environment out there. If in those positions, they are not doing it for other than desire, you have to stop and think about the reasons.

If it were really only a matter of being 40% stronger with no weight penalty, you think you would see it in aircraft and race cars all day long, right? There have got to be reasons that race teams, including everything from 300mph dragsters, Bonneville racers to Ferrari's and Lambo's haven't done it.

You may have plans for your car that we are not privy to that require the use of SS as a core component. Don't let us dissuade you from those plans if they are what you really want to do. Others have made frames from SS and they work fine, but make sure your doing it with the correct information in hand and understand the results of those findings before starting the journey.

KS

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Never become a pessimist. A pessimist is correct oftener than an optimist, but an optimist has more fun, and neither can stop the march of events.-Robert A. Heinlein


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 Post subject: Re: Stainless frame
PostPosted: Sun Aug 08, 2010 4:55 pm 
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Joined: Thu Jul 15, 2010 3:16 pm
Posts: 62
Location: ontario
It sounds like an attractive alternative. My thoughts on this: Stainless can indeed rust, as someone else pointed here. It rusts when deprived of oxygen. This is a known factor in the boat building fraternity and a simple internet search using stainless, rust, boats should provide you with a sampling of horror stories such as rudder posts rusted through and colapsing at the worse time etc. I think that with our little cars there is no substitute for periodic maintenance and if you have to inspect your chassis annually why bother with stainless. My own personal rant about the Seven is that chassis would be a lot more durable if instead of using rivets to join aluminum sheet to mild steel tubes builders were considering other options such as substituting thin sheet steel to aluminum and weld the whole thing. Or alternatively building a frame in aluminum tubes and weld aluminum panels to it. Or even as some have suggested many times here glue aluminum panels to steel tubes using 2 part bonding products. I also believe that a good strategy would be a conventional steel tube chassis sheeted with carbon fiber if you can afford it or glass fiber.

I hope this is of some use to you. Good luck.
Philippe


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 Post subject: Re: Stainless frame
PostPosted: Mon Aug 09, 2010 6:21 pm 
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Posts: 25
Location: Barrie, Ont, Canada
There are a few really long posts that I haven't read so if what I said has been said. disregard.

The thing with stainless is that IT HAS TO HAVE the backs of the welds back purged. Meaning that a shielding gas needs to be inside the tube as well.
This would get highly complicated to continuously set up. failing to purge the backside will result in a black/grey sugar like oxide on the back of the weld. This means the weld is not complete. It doesn't penetrate fully. And is susceptible to cracking from the inside out.

The amount of time and effort that would be required (Not to mention the cost of all the extra gas) would most likely overwhelm the costs of mild steel frame and painting it. that is however, the correct way of welding stainless. I've seen numerous attempts at welding stainless that have not been back purged. More often than not is results in weld failure. With the amount of stress the frame would see. Failing to back purge will certainly result in weld failure(s).

Stainless does in fact rust. It's called StainLESS. Not StainPROOF.
I've been doing sanitary fabrication and repairs (food processing plant) for a while now. Everything HAS to be 316l stainless. Everything HAS to be back purged. Trust me. You DO NOT want to take short cuts with stainless steel. Especially considering how much it cost and there is significantly less room for error. (Stainless likes to work harden. And can become brittle if it's over heated)

This is not to say it cannot be done. It most certainly can. It will just require the proper weld technique, attention to detail, a good understanding of sanitary welding (Back purging), and some pockets that extend a little further than the average person, lol

It should also be noted that Stainless does not like welding gases with C02. Argon only. A slight mix of helium to the argon is okay. But that's best suited for heavy/thccik aluminum.


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 Post subject: Re: Stainless frame
PostPosted: Mon Aug 09, 2010 8:01 pm 
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Location: Michigan
With all the complications, and the higher material cost, has anyone found a price to get a frame hot-dip gavanized?


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 Post subject: Re: Stainless frame
PostPosted: Mon Aug 09, 2010 10:46 pm 
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Quote:
This means the weld is not complete. It doesn't penetrate fully. And is susceptible to cracking from the inside out.


I am continually confused by terminology here. For one thing the difference between penetrating %100 of the material being welded as opposed to %100 of the weld having some penetration. So, I think you are saying if the weld is not all the way thru the base metal, that will cause a stress where the seam is? The bead (MIG) is often a good amount thicker then the base metal though. When a frame is brazed, the bead is allowed to carry the load and it is considered high quality, but not if it's a weld?

I think you have additional requirements because sanitary welding must not allow cracks for bacteria etc. to resist cleaning.

Always happy to get welding advice....

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 Post subject: Re: Stainless frame
PostPosted: Mon Aug 09, 2010 11:00 pm 
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Disclaimer: I AM NOT an expert stainless welder.
I too have heard the the same things about the back-purge when welding stainless tube, I have seen many failures of welds on exhaust and turbo manifolds/headers. most of the time if I am the one fixing it I look at it closely to see if I can find the cause and I have seen the funky looking growth inside when it was not back-purged. I actually went and traded an old cylinder I had for an Argon to use just for back-purge and as a back-up for the TIG. I am a firm believer of back-purging even though I do not know the exact metulurgical reasons for it but I know it seems to work :cheers:
I also second the hot-dip Galvanizing option I have seen it done on Land Rover Defenders so why not a LOCOST chassis......

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 Post subject: Re: Stainless frame
PostPosted: Mon Aug 09, 2010 11:33 pm 
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Location: Phoenix arizona
Im sort of confused really..why do people try to fix something that isnt broken? For 50 years race car builders,bicycle builders,motorcycle builders ..the list goes on..have been building frames out of mild steel..why? um well because it works well and because you dont have to do any tricky welding to make it stick together.Im sure that if collin chapman was reading this hed be asking why people are trying to complicate an easy thing,and yes i totally agree with other comments about why other people havent gone down the stainless road,look 50 years after the first 7 was dreamed of caterham are still making them out of mild steel and until recently were still brazing them together..why..because it never broke..one thing that no one has really touched on is flexing,these things do flex,in fact every race car or bike does and i know from limited experience that stainless does not like to flex..it cracks.


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 Post subject: Re: Stainless frame
PostPosted: Mon Aug 09, 2010 11:53 pm 
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BluEyes wrote:
With all the complications, and the higher material cost, has anyone found a price to get a frame hot-dip gavanized?

I don't know the cost to have a frame galvanized, but where I work they once had mild steel parts hot dipped instead of working form galvanized, and it was quite expensive. you have to send it to a galvanizing shop, and the galvanization is quite thick, rough, and heavy. I would imagine it would be more economical to weld (with adequate protection) a frame from galvanized tube, then cold galvanize the welds (or use zinc stick)

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 Post subject: Re: Stainless frame
PostPosted: Tue Aug 10, 2010 12:05 am 
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Location: Barrie, Ont, Canada
horizenjob wrote:
Quote:
This means the weld is not complete. It doesn't penetrate fully. And is susceptible to cracking from the inside out.


I am continually confused by terminology here. For one thing the difference between penetrating %100 of the material being welded as opposed to %100 of the weld having some penetration. So, I think you are saying if the weld is not all the way thru the base metal, that will cause a stress where the seam is? The bead (MIG) is often a good amount thicker then the base metal though. When a frame is brazed, the bead is allowed to carry the load and it is considered high quality, but not if it's a weld?

I think you have additional requirements because sanitary welding must not allow cracks for bacteria etc. to resist cleaning.

Always happy to get welding advice....


Sorry. You'll have to forgive me. Without noticing. I always refer to welding in TIG welding terms.
Typically. You should be aiming for the weld to penetrate both side of the base material. However, this is usually on butt joints. On T-joints and lap joints penetrating to the other side may not be possible. On thinner materials it will be. But, on thick lap joints and T-joints. You won't be penetrating all the way through to the other side. At that point. You're aiming to have the weld penetration as deep as it is wide.

So, what I mean by "It doesn't penetrate fully", is this. On stainless steel. If the weld does not have a shielding gas on the backside, the oxide the oxygen produces prevents the weld from "burning" into the material.
A crude example.
Lets say you have to 1'' thick stainless plates. With a shielding gas the weld will penetrate the full 1''. Without it. It will only penetrate .5''. Because the oxides (commonly referred to as "sugar" or "sugaring") prevent the weld from going all the way through. And it's the lack of fusion where the sugar is, that weakens the weld. As it is not complete. So it cracks from the inside out.
That's a very crude example.
In reality. The amount of penetration into the material will always vary. Due to material, gas, wire, material thickness, joint type, etc.

In sanitary welding. The backing gas is there to complete the weld. As well as prevent the sugaring. The sugaring will harbor bacteria. So in that case it's a strength thing as well as a cleanliness thing.


BrianG701 wrote:
Disclaimer: I AM NOT an expert stainless welder.
I too have heard the the same things about the back-purge when welding stainless tube, I have seen many failures of welds on exhaust and turbo manifolds/headers. most of the time if I am the one fixing it I look at it closely to see if I can find the cause and I have seen the funky looking growth inside when it was not back-purged. I actually went and traded an old cylinder I had for an Argon to use just for back-purge and as a back-up for the TIG. I am a firm believer of back-purging even though I do not know the exact metulurgical reasons for it but I know it seems to work :cheers:
I also second the hot-dip Galvanizing option I have seen it done on Land Rover Defenders so why not a LOCOST chassis......


Yessir.
It's also just as important to back purge on stainless steel that goes through lots of heat cycles. Like a turbo manifold for instance. If the weld isn't 100% penetrated. When the material heats up and expands, and cools down and contracts. The portion that isn't fused (where the sugar is) will expand. Push up against each other. As well as cool down at a different rate. This puts a lot of stress on the portion of the weld that is complete...

I hope all this makes sense.. I'm kind of groggy and incoherent at the moment. So that may not make sense...

*Edit... I like that it asked me if I was sure I wanted to post in lieu of new posts being added while I was typing.. FANTASTIC FEATURE!!!


wayne-o wrote:
Im sort of confused really..why do people try to fix something that isnt broken? For 50 years race car builders,bicycle builders,motorcycle builders ..the list goes on..have been building frames out of mild steel..why? um well because it works well and because you dont have to do any tricky welding to make it stick together.Im sure that if collin chapman was reading this hed be asking why people are trying to complicate an easy thing,and yes i totally agree with other comments about why other people havent gone down the stainless road,look 50 years after the first 7 was dreamed of caterham are still making them out of mild steel and until recently were still brazing them together..why..because it never broke..one thing that no one has really touched on is flexing,these things do flex,in fact every race car or bike does and i know from limited experience that stainless does not like to flex..it cracks.


This is absolutely correct. Stainless doesn't mix well with two things. Excessive heat (and heat cycles) and flexing.


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