71 replies to this topic

[BritishV8]

I've been researching the Can-Am and Formula A (Formula 5000) cars built by McKee Engineering in the late sixties, which extensively used stainless steel. McKee's last Can-Am car had a thin-gauge stainless steel monocoque chassis! Two of his Formula A cars had stainless spaceframes, and four others mixed stainless tubes into otherwise mild steel spaceframes (because McKee routed water through the frame Lotus-style, but without corrosion). At least seven cars were built with stainless steel suspension components all around.

So, I'm wondering:
1) Did any other racecar constructors try stainless steel for spaceframes?
2) How about for fabricated suspension components?
3) Besides cost, what other disadvantages would appropriate stainless alloys have?

For your enjoyment: here's a snapshot of a McKee Formula 5000 stainless steel spaceframe during restoration:


Some stainless suspension links...


48 additional photos of this car appear here: McKee Mk12 stainless steel Formula 5000 racecar

[Greg Locock]

Even stainless isn't stainless.

Secondly stainless has worse fatigue properties than nice steel, and often has a much lower UTS.

It's hard to weld and maintain its stainlessness.

In that application that lot may be an acceptable tradeoff, but there are good reasons why it is not a general purpose choice for welded structures.

[Tony Matthews]

My very prosaic experience of stainless- versus normal steel as used in fasteners is that it a damn sight easier to wind the head off a stainless wood-screw than a non-stainless of the same size.

[Ray Bell]

From memory, I was once told that stainless nuts and bolts gall easier...

And I know that the stainless studs that hold on my RB30 engine's exhaust stop holding on all too easily when you're tightening the nuts. Snap like carrots, even though they're 10mm.

[Tenmantaylor]

Its only called stainless because it stains less

[McGuire]

Weird how this forum brings up these things. Just last week I got a call from Jim Browning, formerly of Mr. Gasket, later founded Corsa, maker of premium stainless exhaust systems. Did some original work on exhaust sound. Anyway, around 25 years ago he developed and patented a process for fabricating steel tube space frames with thinwall investment castings serving as the tubing joins. As a demo he built a Corvette with an all stainless-steel space frame. Pretty thing. Anyway he has the car and is currently restoring it, hence the phone call. If anyone is interested in the process I just looked up the patent:

http://www.google.co...o...&dq=4660345

[Canuck]

Certain stainless grades gall more readily than others. We build a lot of 17-4 Double H1150 or PH 925 threaded assemblies and without exception, each joint has either copper-plated (as opposed to copper-coat goop) threads or a mating part made of a non-galling material like Ampco, Toughmet or Beryllium copper. 17-4 galls just looking at it.

[gordmac]

Some stainless grades have a lower Young's Modulus, this would give a lower chassis stiffness. Stainless tends to have a much higher thermal expansion coefficient, harder to keep the fabrication dimensionally accurate. Harder to weld in general. Potential fatigue problems.

[McGuire]

Other than being really great looking, I can think of two reasons to build a chassis in stainless steel:

1. Will also be used for food preparation
2. full-boat major team sponsorship from stainless steel company

That's about it I think.

[zac510]

Very droll, Bernard

[malbear]

[quote name='Ray Bell' date='Jan 26 2010, 01:37' post='4095558']
From memory, I was once told that stainless nuts and bolts gall easier...

Helicoils are stainless . They don't seem to gall. I guess they did a lot of research on the grade of stainless.
Malbeare

[cheapracer]

Other than being really great looking, I can think of two reasons to build a chassis in stainless steel:

1. Will also be used for food preparation
2. full-boat major team sponsorship from stainless steel company

That's about it I think.

+1

I can't think of a single reason why he would do the chassis in SS unless he obviously had access to it for free.

Unless he stored or raced it next to the ocean and was fed up with previous chassis rusting out?

Did anyone mention the welding yet, pain in the ass also and I'm sure harder back then.

[BritishV8]

Are you guys kidding me? 304 is EASY to TIG weld if you're set up for it. McKee Engineering obviously was. (Apparently their competitors were mostly still using oxy-acetylene.)

Bonus: you never have to remove rust from stainless steel before welding it.

Unlike 4130, you don't need to heat treat afterwards.

Typical UTS of mild steel: ~64,000psi
Typical UTS of Grade 304 (18/8) stainless: ~85,000psi
(You do give up a little bit in rigidity... ~193GPa vs. about ~205GPa.)

Last time we built a spaceframe out of mild steel, it took about a day to paint it and then we had to wait for the paint to dry. Then, since we were putting aluminum stressed skins on it, we had to sand half that paint off before applying adhesive. That's a lot of wasted time! (I suppose we could have masked... but that's time too.)

Then, everytime we wanted to repair or modify the frame we had to remove old paint (and sometimes some corrosion), and after the repair we had to fuss with applying new paint. Over time, paint gets all chipped up and looks unprofessional, thus more maintenance costs.

Did you read the article? Like Lotus, McKee was running coolant through frame tubes to a front-mounted radiator. The stainless tubes were obviously better suited to this old trick, whereas old Lotus frames (e.g. Lotus 51 Formula Fords) have lots of internal corrosion issues.

Edited by BritishV8, 26 January 2010 - 22:47.

[Lee Nicolle]

Having just had a boilermaker/ welder mate in he says that most grades of stainless are easy to tigweld, but a lot get more brittle. he reckons that moly is stronger and suffers less from heat embrittlement than any stainless, as do premium mild steels suited for rollcages etc.
But if welded well with more thought on weld placement he reckons that it should work ok. But he will use the right steel everytime for rollcages in preference as it is simple to weld and far cheaper than stainless or moly. And is not a great deal heavier.
I have heard the same from a couple of professional cage/ chassis builders. also TIG welds are not as strong as MIG. Actually the old nickel bronze is stronger on steel.

[gruntguru]

Helicoils are stainless . They don't seem to gall. I guess they did a lot of research on the grade of stainless.

Galling occurs when mating stainles to stainless. Normally the bolt being screwed into the helicoil will be a different material to the helicoil.

[cheapracer]

Are you guys kidding me? 304 is EASY to TIG weld if you're set up for it. McKee Engineering obviously was. (Apparently their competitors were mostly still using oxy-acetylene.)

classic.

[Catalina Park]

Did you read the article? Like Lotus, McKee was running coolant through frame tubes to a front-mounted radiator. The stainless tubes were obviously better suited to this old trick, whereas old Lotus frames (e.g. Lotus 51 Formula Fords) have lots of internal corrosion issues.

I wonder if the thermal expansion was taken into account?
Imagine the effects when the pipe from the engine to radiator grows faster than the pipe from the radiator to the engine.
That would be why most clever designers gave this idea a miss.

[Tony Matthews]

That would be why most clever designers gave this idea a miss.

Might be handy on an oval...

[Ben Wilson]

Apparently Reynard use stainless for the chassis of the Inverter.

[McGuire]

Are you guys kidding me?

I am not knocking my friend Bob McKee in any way. He's a brilliant guy. The 60's was a time for experimenting with exciting new substances. The world was young and full of possibilities. That's why the cars of the era are so interesting today in their great variety and originality.

[BritishV8]

Apparently Reynard use stainless for the chassis of the Inverter.

Cool! There isn't much detailed info on the Reynard Inverter website...
"Chassis: 55kg Stainless Steel with composite panel stiffeners to 750mc regulations. FIA chassis available on request"

Perhaps Adrian Reynard's world is still "young and full of possibilities."

[BritishV8]

Not just the roll hoop... this photo shows some stainless box tubing and sheetmetal too.

Looks like the upper rear control arms are stainless, doesn't it?

[BritishV8]

I wonder if the thermal expansion was taken into account?
Imagine the effects when the pipe from the engine to radiator grows faster than the pipe from the radiator to the engine.
That would be why most clever designers gave this idea a miss.

Just because I was curious to quantify the problem...

Coefficient of thermal expansion:
mild steel (1020) = 11.7x10^-6/C
Chrome Moly (4140) = 12.2x10^-6/C
Grade 304 stainless = 17.2x10^-6/C
Grade 316 stainless = 15.9x10^-6/C
(Worst case is grade 304...)

Assuming 1.5m long tube, 20C ambient, 100C coolant, and no bending of the tube due to other structure:
mild steel like Lotus used => 1.5 x (100-80) x 11.7 / 1000 = 1.4mm
Grade 304 like McKee used => 1.5 x (100-80) x 17.2 / 1000 = 2.1mm

[dosco]

Are you guys kidding me? 304 is EASY to TIG weld if you're set up for it. McKee Engineering obviously was. (Apparently their competitors were mostly still using oxy-acetylene.)

316 and 321 are relatively straighforward to GTAW, IME 304 and 306 had problems with hot-fastness. I'm not sure I would charaterize the process as "easy." Stick welding stainless is a bitch.

Bonus: you never have to remove rust from stainless steel before welding it.

I wouldn't take that home to the bank. In critical welds, iron and its relatives need to be removed from the surface of the stainless by virtue of passivation to restore the chromium layer on the surface. If not the iron will rust in place and become a focal point for corrosion on the surface of the stainless.

Unlike 4130, you don't need to heat treat afterwards.

Depends on the application. In 300-series stainless the carbides that form in the heat-affected zone are susceptible to corrosion by certain acids. To fully restore the corrosion-resistant properties of the material it needs to be fully solution-annealed (e.g. heat treated).

[zac510]

Cool! There isn't much detailed info on the Reynard Inverter website...
"Chassis: 55kg Stainless Steel with composite panel stiffeners to 750mc regulations. FIA chassis available on request"

Wonder what the FIA chassis is made of?

[dosco]

Wonder what the FIA chassis is made of?

Neutronium.

[J. Edlund]

High strength compared to mild steel but lower strength than normalized 4140 chrome moly steel.

Fatigue limit at roughly 0.2% strength level or approximatly 240 MPa for 304, 270 MPa for 316 and 260 MPa för 321. At roughly 50% of UTS for duplex stainless.

+50% elongation at break combined with a reasonable high strength for 300-series stainless offers excellent crash safety.

Good ductility, excellent ductility at low temperatures.

Can be 'poisoned' by mild steel, causing it to rust.

Slightly lower specific stiffness than non stainless steel.

Should be TIG welded in a protected environment and passivated.

321 is alloyed to prevent the formation of chromium carbide at high temperatures.

[cheapracer]

316 and 321 are relatively straighforward to GTAW, IME 304 and 306 had problems with hot-fastness. I'm not sure I would charaterize the process as "easy." Stick welding stainless is a bitch.

Wasn't what I found amusing, how many here in the 60's or 70's had some TIG welding to be done and thought "I'll just nick down to the local welders......."

It's easy today but specialised TIG, MIG etc. welders in and around Melbourne were a little thin on the ground back then as i imagine everywhere else.

Neutronium.

With testouri rivets apparently.

Edited by cheapracer, 28 January 2010 - 10:12.

[NeilR]

*cue four yorkshire men sitting in chairs*
"A hovel!...you were lucky lad! we lived in a hole in the 't ground in Melbourne and bite the heads of pigeons 'coz black puddin was too expensive for the likes of uz...and...AND we had to walk five miles in the pouring rain to get 't bit of welding done!"

[Tony Matthews]

Ay! 'Appen! Welding? Get a bit o' welding done? You were lucky! If we wanted welding done we 'ad ter do it oursen, wi' a box o' Swan Vestas an' a jar of grinding-wheel sparks! Pigeons? Don't mek me laff, lad! We 'ad to pick over t' remains o' pigeons what the rats left uz!

[McGuire]

Wasn't what I found amusing, how many here in the 60's or 70's had some TIG welding to be done and thought "I'll just nick down to the local welders......."

It's easy today but specialised TIG, MIG etc. welders in and around Melbourne were a little thin on the ground back then as i imagine everywhere else.

By the '60s most all quality race shops in the USA had TIG capability, then more commonly known as Heliarc. The Indy roadsters were invariably chrome-moly and Heliarc construction, for example.

Much of this expertise was picked up during WWII in military facilities and defense plants. After the war guys brought it home and put it to use on their race cars and hot rods. This is also how braided fluid lines, Dzus fasteners, pulled rivets, etc, in race cars originated. The tools and materials could be purchased for pennies on the dollar in war surplus outlets well into the '60s. (One of the familiar suppliers of braided racing hose actually started out as an army-navy surplus store.) During the war, much of the aircraft industry was centered around Los Angeles, and after the war many workers and returning GIs settled there. The cars they built became known "west coast" or "LA'ed to the max": Chrome-moly, Heliarc, Aeroquip everything, rolled panels, etc. Then often topped off with candy-apple paint, gold leaf, and pin striping by Von Dutch or Tommy the Greek. Works of art. The resistance to the rear-engine revolution at Indy was not all about engine placement. They took a look at some of Chapman's more questionable construction techniques and said WTF is that.

Strange but true: the man who developed Aeroquip braided line, Peter Hurst, was not allowed in his own plant. He was technically a German national and thus a security risk.

[Canuck]

When I took my TIG course, the instructor communicated that, in his opinion, 90% or more of all TIG welding could be done by oxy/acetylene rigs equally well and that TIG had risen to it's sought-after status by myth more than need. Is that true? I was looking at welding up hand-formed aluminium bodywork at the time and was under the impression TIG was the way to go. I don't regret my choice, but his comments always left me wondering.

McGuire - your extensive repository of Peter Hurst-like stories never ceases to amaze me. I truly enjoy reading your story behind the story posts.

[dosco]

When I took my TIG course, the instructor communicated that, in his opinion, 90% or more of all TIG welding could be done by oxy/acetylene rigs equally well and that TIG had risen to it's sought-after status by myth more than need. Is that true? I was looking at welding up hand-formed aluminium bodywork at the time and was under the impression TIG was the way to go. I don't regret my choice, but his comments always left me wondering.

Without understanding the context of his comment it's hard to say.

If you're talking about welding many steel alloys, he was probably right. Stick or oxyfuel welding of steel is pretty straightforward and has been done that way for a long time.

For alloys like titanium, inconel, and stainless, I would strongly disagree. Processes that prevent oxidation during welding are a necessity for these materials due to their propensity to oxidize and contaminate the weld (although other methods like EB welding can also prevent oxidation). I've read in a few places about oxyfuel welding of stainless, but I have a hard time buying that.

For aluminum, I seem to recall reading something somewhere that some aluminum alloys are weldable using oxyfuel processes. This website talks about oxyfuel welding of aluminum.

Also, I suspect that it is easier to control welding process variables using GTAW when compared to oxyfuel due to the ease of specifying amps, tungsten sizes, inert gas flow rate, etc. in a process sheet.

[NeilR]

My grandfather was a coach builder for Humber limo's. All ali welding was by gas, partly because the joint was soft and as formable as the rest of the panel - there was no filler rod, just a thin strip of ali cut off the sheet. I suspect there was also tradition behind it..."we've always done it this way" thoughts. By the same token all his paint work was multi layers of enamel - the higher the price car the more layers, all hand rubbed between coats.

[Lee Nicolle]

When I took my TIG course, the instructor communicated that, in his opinion, 90% or more of all TIG welding could be done by oxy/acetylene rigs equally well and that TIG had risen to it's sought-after status by myth more than need. Is that true? I was looking at welding up hand-formed aluminium bodywork at the time and was under the impression TIG was the way to go. I don't regret my choice, but his comments always left me wondering.

McGuire - your extensive repository of Peter Hurst-like stories never ceases to amaze me. I truly enjoy reading your story behind the story posts.

You will get a lot less heat distortion welding sheet metal with a TIG [or MIG]. Though I have seen tradies weld both alloy and steel sheet with oxy with very little distortion. Not me though, though I can weld up thin rusty exhausts very well with the oxy. But sheet metal pulls everwhere.A bit better brazing. I am not bad though with the MIG. Have ever only used TIG once and did not like it though good people do lovely neat work with it.

[dosco]

You will get a lot less heat distortion welding sheet metal with a TIG [or MIG]. Though I have seen tradies weld both alloy and steel sheet with oxy with very little distortion. Not me though, though I can weld up thin rusty exhausts very well with the oxy. But sheet metal pulls everwhere.A bit better brazing. I am not bad though with the MIG. Have ever only used TIG once and did not like it though good people do lovely neat work with it.

One issue that I see with GMAW welds is poor start and rampouts with associated cratering. I see it all the time in welded aluminum. A buddy has a ramp to wheel his motorcycle onto his pickup truck, every weld rampout is cracked to hell. Oy.

Edited by dosco, 29 January 2010 - 03:49.

[McGuire]

My grandfather was a coach builder for Humber limo's. All ali welding was by gas, partly because the joint was soft and as formable as the rest of the panel - there was no filler rod, just a thin strip of ali cut off the sheet.

You gave away the secret. The second trick is green goggles; the third trick is good flux. (Alladin for one.) I was taught these and other tricks by an ex-girlfriend who was a welder in nuclear power plants. Five feet tall, 100 lbs, best welder I ever saw. We shared a shop for awhile where she did ornamental iron and metal sculpture. As a prank she could gas-weld a soda can to an aluminum step ladder, took her about two seconds.

I really enjoy gas welding. Very satisfying and you can see what you are doing. Just time-consuming which is not all bad.

Getting back on topic, stainless steel space frames... as with so many things, as a "why not" sort of proposition it works but as a "why" proposition, not quite as well. The corrosion angle is not terribly persuasive in that the service life of a Lotus frame was around .9 seasons anyway.

Edited by McGuire, 29 January 2010 - 15:10.

[Catalina Park]

Just because I was curious to quantify the problem...

Coefficient of thermal expansion:
mild steel (1020) = 11.7x10^-6/C
Chrome Moly (4140) = 12.2x10^-6/C
Grade 304 stainless = 17.2x10^-6/C
Grade 316 stainless = 15.9x10^-6/C
(Worst case is grade 304...)

Assuming 1.5m long tube, 20C ambient, 100C coolant, and no bending of the tube due to other structure:
mild steel like Lotus used => 1.5 x (100-80) x 11.7 / 1000 = 1.4mm
Grade 304 like McKee used => 1.5 x (100-80) x 17.2 / 1000 = 2.1mm

My point was not the difference in thermal expansion of stainless compared to mild steel. My point was the difference in thermal expansion of using a chassis as a pipeline compared to using the chassis as an accurate structure to hang suspension on.
Take your figures of mild steel at 1.4mm and stainless at 2.1mm and compare that to not having the tubes heating up with oil and coolant.

[Engineguy]

Weird how this forum brings up these things. Just last week I got a call from Jim Browning, formerly of Mr. Gasket, later founded Corsa, maker of premium stainless exhaust systems. Did some original work on exhaust sound. Anyway, around 25 years ago he developed and patented a process for fabricating steel tube space frames with thinwall investment castings serving as the tubing joins. As a demo he built a Corvette with an all stainless-steel space frame. Pretty thing...

Gee, I thought I was the only one with that little tidbit stuck in my mind (not the who, just the what). Seems like Hot Rod did a big deal on it, maybe even a cover story? Like it was gonna be a big thing and totally replace conventional mild steel fishmouth tube frame construction. I remember assuming it would be too expensive and that you'd have to design around the selection of fittings which might be limiting.
.

[cheapracer]

Gee, I thought I was the only one with that little tidbit stuck in my mind (not the who, just the what). Seems like Hot Rod did a big deal on it, maybe even a cover story? Like it was gonna be a big thing and totally replace conventional mild steel fishmouth tube frame construction. I remember assuming it would be too expensive and that you'd have to design around the selection of fittings which might be limiting.
.

Oh, DUH, I just now cottoned onto what you guys are on about.

I came very close to the same thing myself as I was building the current project and it's not still out of the question. The amount of time it would save for me for production would be awesome (consider I run the 2 big spars with the intersecting bracing tubes, thats 20 fishmouths there alone) and I was figuring on one style of pivoting units if I could get them to look neat.

[Tony Matthews]

Oh, DUH, I just now cottoned onto what you guys are on about.

I came very close to the same thing myself as I was building the current project and it's not still out of the question. The amount of time it would save for me for production would be awesome (consider I run the 2 big spars with the intersecting bracing tubes, thats 20 fishmouths there alone) and I was figuring on one style of pivoting units if I could get them to look neat.

Try Dexion.

[cheapracer]

Try Dexion.

No need Mate, been off the chile this last week and my guts are just fine but thanks

[kikiturbo2]

Oh, DUH, I just now cottoned onto what you guys are on about.

I came very close to the same thing myself as I was building the current project and it's not still out of the question. The amount of time it would save for me for production would be awesome (consider I run the 2 big spars with the intersecting bracing tubes, thats 20 fishmouths there alone) and I was figuring on one style of pivoting units if I could get them to look neat.

wouldn't a CNC laser tubing cutter be a much better solution..? for serial production of course..

I have about 40 fishmouths in just the front part of the frame carrying the front suspension..


when I finish the frame, I'll count all the fishmouths I did by hand with a grinder and go for a loooong drink..

[threep]

I've not much experience of stainless, but I do remember the pain I had trying to drill some holes in some brackets I had made up to mount bucket seats my road rally car. It was aerospace grade stainless from work, I went through a number of bits just trying to drill a handfull of holes

[kikiturbo2]

some time ago I got a brochure from tennant metall for some new stainless that had 980 N/mm2 UTS... Unfortunately, no more about it, but did sound interesting for an expensive exoskeleton car..

[McGuire]

Gee, I thought I was the only one with that little tidbit stuck in my mind (not the who, just the what). Seems like Hot Rod did a big deal on it, maybe even a cover story? Like it was gonna be a big thing and totally replace conventional mild steel fishmouth tube frame construction. I remember assuming it would be too expensive and that you'd have to design around the selection of fittings which might be limiting.
.

Yep that's the one.

The idea has also been resurrected/adapted recently by Bret Voelkel at Air Ride Technologies (the air suspension company) to produce bolt-in roll cages for those who want to use their rare and valuable collector cars for track days and so forth -- the theory being that this deal can be installed without hacking the car to pieces as with a conventional weld-in cage, then easily removed for vehicle resale, etc. Also, that most anyone could install it regardless of their lack of fab skills. The hangup appears to be getting sanctioning body certifications.

http://www.ridetech....ategory_id=1828

[McGuire]

when I finish the frame, I'll count all the fishmouths I did by hand with a grinder and go for a loooong drink..

http://www.aircrafts...pipenotcher.php

[kikiturbo2]

http://www.aircrafts...pipenotcher.php

actually.. I made one of those myself, but had problems aligning the cuts between the two ends of the tube.... My method with the cut sticker ended up being much more accurate and faster... Kind of poor mans laser cutting..

[gruntguru]

actually.. I made one of those myself, but had problems aligning the cuts between the two ends of the tube.... My method with the cut sticker ended up being much more accurate and faster... Kind of poor mans laser cutting..

And of course you can remove 99% of the metal by making one appropriately angled cut for each scallop using your cut-off saw. The last 1% with die grinder.

[kikiturbo2]

I first do a rough cut with a grinder and a thin cut off disc, then I take another grinder with a thick grinding disc and finish it off with that..

Edited by kikiturbo2, 12 February 2010 - 05:28.