F1technical.net

Hi all,

This might become a very simple & short topic, but haven't really found a conclusive answer elsewhere;

Currently building a custom-spec (gravel) rally car. Full tubular chassis, double wishbone, FWD car.
Uprights are designed out of sheet metal parts. These were intended to be lasercut out of ordinary steel (S235 or S355). Bended & welded together. However, I have been presented with the opportunity to water jet cut anything sheet metal for free, as long as it's made out of 304 (stainless steel).
Since building any racing car sometimes simply comes down to what's easiest or most practical to use instead of going for the all-out perfect solution, I would rather not let this opportunity go unused.

So, simple question, any reasons not to use stainless steel (304) for upright construction? Can't really find any reason not to, but rather ask the experts as to not overlook anything. Anything fatigue or thermal related perhaps??

many thanks.
-Tom

Looking at the yield strength it’s a rather soft material, so you might need to adjust material thickness which adds weight.

also ..... not so easy to weld in this quite thin section fabrication ??
threads would be quite weak and it doesn't tap or machine well

being inherently soft it is far from having a fatigue issue
having a high melting point it's pretty heatproof
should be ok if it's free
the mechanical properties of many steels and ferritic and martensitic stainless steels are much better 'on paper'
but not particularly beneficial in this application

Welding Stainless requires purging of the Welding bed backside in the Same Way as titanium so an innert Gas welding chamber is recommended for high Quality results .otherwise You get
noodges on the backside and reduced weld strength.stainless Trends to galling as well so threads may be a bit tricky.

Lots of good reasons cited here. You're right that sometimes it comes down to easiest and most practical solution - I think cutting your stuff from 4130 is most practical. Not really that expensive either.

Properly done 304 welded uprights with a skilled TIG guy would probably look damn good, though. With a not-so-good welder and without proper setup.. can look like crap.

Also, figure you'll probably have to do some post-weld machining on these parts.. 304 not super fun on that front, especially if you want high tolerance bearing surfaces for say a wheel bearing.

You could helicoil all the bolts to get round the galling issue. Also, 304 is 'stainless' but will actually rust in the right environment, even if not welded, depending on the supplier.

Greg Locock wrote:You could helicoil all the bolts to get round the galling issue.

Further going down the pain in the rear route

This gives rise to an aphorism like the one "Just because you're paranoid doesn't mean they aren't really out to get you." :

"Just because it's free doesn't mean it's the right way to go."

I saw a TV show about German apprentice machinists. Part of their final exam consisted of being given an irregular rough block of steel, a micrometer, a square, a file, and the requirement to present a square block to very close tolerances. Just break out your hacksaw, air grinder, and files and cut those suckers out of 4130 sheet.

Just weight, eventually you will want to go to alloy, i see it so often, here is my Chevron GR8 with a Ferrari 360 Modena engine and transmission that im building with billet alloy uprights, then you can get them anodised as i did.

http://www.f1technical.net/forum/viewto ... 460#unread

I hope you stressed them out carefully, aluminium uprights are certainly possible in production, but we used forged parts, not machined from billet. The difference is that the forging improves the properties of the alloy and possibly aligns the grain structure of the alloy with the structure (supposedly an advantage of forged steel)

Horses for courses here, as always .
If you have no Access to anything Else than 304 -it can be Used .but you Need A Lot of Specialist Equipment and Expertise or it will turn out quite Heavy and bulky as you have to compensate for manufacturing shortcomings.
Maybe a wiser approach would be to Start off with something better suited to your recources...mild Steel for that matter and venture into more involved Materials as You Build up Knowledge and capabilities and See no other possibility to improve Performance!

Chevron GR8 Ferrari wrote:Just weight, eventually you will want to go to alloy, i see it so often, here is my Chevron GR8 with a Ferrari 360 Modena engine and transmission that im building with billet alloy uprights, then you can get them anodised as i did.

http://www.youtube.com/watch?v=Y4J1AwqenTo

I've never understood the hardon people get over "billet" parts. As Greg mentioned, forged parts are much stronger and resistent to fatigue. In my opinion fabricated steel parts also are more efficient in terms of material usage (since steel and ally have a similat specific density).

In production cars, machined parts are an absolute last resort since they are weaker, more expensive and take longer to produce than a forged part.

But, just weight till you anodise them...

Greg Locock wrote:I hope you stressed them out carefully, aluminium uprights are certainly possible in production, but we used forged parts, not machined from billet. The difference is that the forging improves the properties of the alloy and possibly aligns the grain structure of the alloy with the structure (supposedly an advantage of forged steel)

forging meaning hot forging, ie reshaping at a temperature high enough for plasticity (of precursor material inevitably cast once)
forging does not, correctly speaking, improve the metal either in strength or in stiffness
(metal's priceless value is its isotropy of strength and stiffness, ie meaningfully speaking it doesn't have a 'grain')
forging manages the alignment of inhomogenieties in the metal to disperse (and prevent concentration of) their adverse effects
this alignment is unfortunately characterised as 'grain'
inhomogenieties eg from oxidation and other effects are generally unavoidable
casting inherently generates various inhomogenieties
so forging is the best of a bad bunch (of general production techniques)

@ Tim's point
billet used to mean (by implication) forged billet (and the part designed accordingly)
otherwise it means little, or worse
(forging can anyway be used to re-size material, eg to 'bump up' eg 6" bar to 8")

aluminium alloys are only as good as the precursor
a nice big lump will be liable to grain growth from the slow cooling, and so may be relatively weak
often there is some recognised relationship between properties and size

Tim.Wright wrote:I've never understood the hardon people get over "billet" parts. [...] In production cars, machined parts are an absolute last resort since they are weaker, more expensive and take longer to produce than a forged part.

In a production environment, sure.

There are some really nice advantages of billet parts though. For a small batch, I can have a few sets done in a day (including programming and setup time but not including if I need to send them out for surface treatment). Plus, I know exactly what the part geometry is to high precision, and have a good idea of homogeneous, minimum mechanical properties of the material.

Tommy Cookers wrote:forging meaning hot forging

Just going to skip over cold forging then?

So, turned out there was much more to this than I originally thought! Galling wasn't of any importance, the only thing threaded into the upright was ever going to be the speed sensor.

Many thanks for all your input! I will now acquire me some 4130 sheet.

kind regards,
Tom