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 Post subject: stainless steel chassis
PostPosted: Thu Jul 21, 2011 5:59 pm 
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Location: central Arkansas
I was by my favorite steelyard today, and asked about 18 or 20 gauge 1x1 square tubing while I was there. They said those were odd sizes that they'd have to special order... but they could give me a smokin' deal on some 1x1x18ga stainless or some 1-1/4x1-1/4 brushed stainless tube. They have (literally) tons of the stuff on hand.

I was so surprised I forgot to ask whether it was 3xx or 4xx alloy. When I got home I found that stainless MIG wire isn't much more than ordinary MIG wire.

Stainless is a pain in the ass to work with, but the wow factor on a stainless chassis would be high...


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PostPosted: Thu Jul 21, 2011 6:40 pm 
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Dr Hess' chassis is stainless. He is in Fayetteville, Ar

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PostPosted: Thu Jul 21, 2011 11:37 pm 
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Quote:
Stainless is a pain in the ass to work with


Stainless is only a PITA if you're machining it. It is an absolute dream to weld. Take it from someone with many years under his belt as a maintenance mech in the food industry.

On a side note, I visited Dr. Hess at his home just before the Midwest Gathering. His Locost, called "The Papillon", is a very impressive piece of work. One thing struck me as quite odd, though. The car does indeed have a S/S frame. It also has the usual mix of aluminum & fiberglass body panels. What seemed unusual to me was the fact that he painted the car with Rust-Oleum :? Talk about a "belt-&-suspenders" plan to avoid corrosion!

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PostPosted: Fri Jul 22, 2011 3:23 am 
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http://www.locostusa.com/forums/viewtopic.php?f=39&t=9901&start=0

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PostPosted: Fri Jul 22, 2011 9:48 am 
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The voice of reason
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Some folks use 18 gauge for track cars. I think it raises the bar a good step in terms of knowing how to put one of these cars together and also periodic maintenance for crack checking etc.

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PostPosted: Fri Jul 22, 2011 10:11 am 
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horizenjob wrote:
Some folks use 18 gauge for track cars. I think it raises the bar a good step in terms of knowing how to put one of these cars together and also periodic maintenance for crack checking etc.


Would you use the same gauge stainless as you would use of mild steel (16 ga x say 1.250 for a track day / autocross high powered car - (4 - 6 lb/horse))? How do they compare strength wise?

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PostPosted: Fri Jul 22, 2011 10:37 am 
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I may be mistaken but I always thought stainless was somewhat more brittle than carbon steel? Maybe not, or maybe not enough to be an issue.

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PostPosted: Fri Jul 22, 2011 10:59 am 
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I believe that is true, but even Carroll Smith, whom we often look to for inspiration, shows a very strong preference for stainless in a race car chassis over mild steel, which he seems to feel is best suited for shop fixtures. That said, he also strongly emphasizes that proper preparation, welding techniques and full chassis normalization & heat treating are essential when working with stainless. I am neither an engineer or experienced welder, so have no relevant experience or specialized knowledge to draw from.

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PostPosted: Mon Jul 25, 2011 7:11 am 
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I would steer clear from using stainless for your chassis. While it may be a little stronger than MS it is also harder. It does not drill easily and will suffer from embrittlement especially around your welds. It is weldable with the mig but is ugly and is best welded with tig and both need an Argon gas. It is also best purge welded as the undersides of your welds suffer badly with exposure to the air. Not for me thanks.
Bruce


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PostPosted: Mon Jul 25, 2011 9:52 am 
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I've been told you should back purge even for mild steel. Probably more important for 18 gauge too. I'll try to remember to look inside soe of my welding practice pieces, one of these days.

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SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
Car9 Roadster information - models, drawings, resources etc.


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PostPosted: Mon Jul 25, 2011 10:09 am 
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I don't have big objections to different materials for construction of our cars. The important thing to understand is where you are when you step away from our common practice. You quickly become a pioneer with much less history of design and practice.

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Car9 Roadster information - models, drawings, resources etc.


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PostPosted: Mon Jul 25, 2011 10:14 am 
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I had a stainless steel diving knife - it rusted.
We have a stainless steel sink strainer - it's rusted on the welds.
I welded up a stainless steel process tank for our fish pond - it has rusty welds.

When stainless is welded, it drives the chromium (I believe) out of the weld, removing the non-rust quality of the metal. Granted, the above cases are worst-case because of the direct exposure to water, but it'll still happen in moist air, just slower. Stainless can and will rust if it's been welded.

Somewhat related to safety, lets say it doesn't rust at all. Do you really want a super-shiny chassis blinding you with reflections of the sun off every tube?

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PostPosted: Mon Jul 25, 2011 7:30 pm 
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Same misinformation, different day.

I'm neither a metallurgist nor an engineer. However, for 30 years, I designed boilers, heat exchangers, textile and chemical processing equipment, pumps, valves, piping systems and heaven-knows-what else, mostly in 300 series stainless steels. Pretty much all the complaints here are true in a very narrow sense, and wrong in practical use.

If you are interested in using 300 series stainless in your build-and I would not recommend any other alloy- then go to the Sandmeyer website, click on Technical Information, and read, read, read.

http://www.sandmeyersteel.com/


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PostPosted: Thu Aug 04, 2011 1:08 pm 
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I was at the steelyard again this morning and talked to them about the stainless. The 1" mill finish stuff is 304 alloy.


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PostPosted: Thu Aug 04, 2011 1:58 pm 
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Regarding the proper stainless, practicality dictates that we builders use whatever's available in the scrap yard or steel shop. Rarely do we have a wide choice of alloys, so we get what we get. My statements regarding stainless rusting stand, as "304" (most often without any suffix) is what's most typically available to builders, and is what has rusted for me after welding (using 309 rod.) So while there may be alloys that don't rust on the welds, it can be more difficult to find, more expensive, or both. For that and other reasons I went with mild steel.

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