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Period materials that are unobtainable?


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#1 Charlieman

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Posted 02 August 2014 - 19:04

If I wished to build a perfect replica of a racing car (name your preferred era) using authentic materials and using period manufacturing techniques, how close could I get?

 

This is a thought experiment; I'm not trying to fake a racing car. I'm assuming hypothetically that I could source an original engine, gearbox and other proprietary forged or cast components. I'm thinking about the difficulty of sourcing correct gauge and composition steel and aluminium alloy (sheet, bar, tube). Thinking a bit harder, I'll add less obvious materials such as brass, rubber and chopped strand mat. Wiring loom? Plus I'd need to have access to period metal forming equipment, welding kit and plating apparatus.

 

We have all seen fabulous recreations and restorations of old cars. They are glorious and we tolerate 'fakery' (modern materials in fuel and electrical lines) for good reason.

 

A 1950s racing body was made from Duralumin, a trade name so we can assume that most bodies were made from something else which was like Duralumin. Could I buy the 'real thing' today?



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#2 Siddley

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Posted 02 August 2014 - 20:48

I'm pretty sure you'd be OK with dural. I used to buy it as 'bar end' offcuts from an aerospace company until fairly recently. Some of it was 'broad arrow' marked, so there is a military requirement for it. I didn't buy sheet, but I expect it's available.
Then there is 'Birmabright', the alloy which Land Rover bodies are made from - that must have found it's way into period racing cars.

I can't think of much you couldn't source one way or another.
 



#3 Charlieman

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Posted 02 August 2014 - 22:11

Ta, Siddley. When you are buying bar, you can make what you want from it.

 

If you are buying sheet or tube, form is more difficult. Even if you find the same material, can you find something with old dimensions?



#4 kayemod

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Posted 02 August 2014 - 22:19

... and chopped strand mat.

 

Could I buy the 'real thing' today?

 

Certainly no problem with that, or any other "old fashioned" GRP materials, they're all still readily available. How much do you need?



#5 GMACKIE

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Posted 02 August 2014 - 22:44

Depending on the material, sheets were usually in Standard Wire Gauge [SWG], or Birmingham Gauge [BG].......anyone know what these are in milli-bloody-metres ? :)



#6 kayemod

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Posted 02 August 2014 - 22:56

Depending on the material, sheets were usually in Standard Wire Gauge [SWG], or Birmingham Gauge [BG].......anyone know what these are in milli-bloody-metres ? :)

 

Some of these materials haven't been metricated quite as much as it might appear at first sght. Depending on the machinery they're made with, some items have been given nominal metric tags even though they are exactly the same as the imperial, SWG etc sizes that our fathers and grandfathers used to buy. My knowledge of this comes mainly from some specialist timber dimensions, which I've seen on sale in France in 910mm units, which is of course 36" or one yard, though I doubt if unsuspecting French purchasers know this, they'd probably start blocking roads by burning the stuff if they knew.



#7 Charlieman

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Posted 02 August 2014 - 22:59

Certainly no problem with that, or any other "old fashioned" GRP materials, they're all still readily available. How much do you need?

I can get fibre at the boat yard. Can I get the same polys to glue it together?



#8 Charlieman

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Posted 02 August 2014 - 23:17

 

Depending on the material, sheets were usually in Standard Wire Gauge [SWG], or Birmingham Gauge [BG].......anyone know what these are in milli-bloody-metres ? :)

 

Some of these materials haven't been metricated...

My hypothetical car build requires that I find original spec materials. Sub-milimetre would be required tolerance and knowledge about processes which have been metricated might be helpful. Assume that I seek Inches and SWG, but wish to learn, out of nosiness, how Italians, Germans and the French might dimension racing cars.



#9 Siddley

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Posted 03 August 2014 - 00:20

Ta, Siddley. When you are buying bar, you can make what you want from it.

 

If you are buying sheet or tube, form is more difficult. Even if you find the same material, can you find something with old dimensions?

 I'm not speaking with authority but I have noticed that metal suppliers offer material which is nominally metric, but when you actually mike it then it turns out to be pretty much dead on a fractional or decimal imperial size and just very close to the metric dimension they quoted.

I don't do sheet metal work so I'm not very clued up on sizes.

I'll mike some of my remaining stock of dural tomorrow and see what transpires. It'll be a great excuse to use my GKN 'Speedread' micrometer - it's got a mechanical digital display and is built like a swiss watch. I usually work in metric so it doesn't get a lot of use....

If you take the project from theory to practice I've got a lot of aerospace grade titanium that needs a good home  ;)



#10 GMACKIE

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Posted 03 August 2014 - 00:39

That 'Speedread' micrometer would be handy. :up:  The two main gauges used in sheet metal [BG & SWG] differ considerably :-

 

http://cattlecorner....tmetalgauge.htm



#11 Charlieman

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Posted 03 August 2014 - 00:55

If you take the project from theory to practice I've got a lot of aerospace grade titanium that needs a good home  ;)

Titanium would be inappropriate on a Brabham...

 

I don't know how to pose a polite question. When constructing a new wishbone for a 1960s racer, which metal would you pick?  Period or contemporary?



#12 GMACKIE

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Posted 03 August 2014 - 01:20

 

 

I don't know how to pose a polite question. When constructing a new wishbone for a 1960s racer, which metal would you pick?  Period or contemporary?

Whichever is the least likely to break.  ;)



#13 brucemoxon

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Posted 03 August 2014 - 01:27

How about brake and clutch linings? No asbestos now. Or bakelite for switches, steering wheels and badges.

Lead to fill body imperfections, more asbestos for gaskets, more lead in the paint...

 

How about cloth wiring insulation?

 

 

 

 

Bruce Moxon



#14 Charlieman

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Posted 03 August 2014 - 03:23

How about brake and clutch linings? No asbestos now. Or bakelite for switches, steering wheels and badges.

Lead to fill body imperfections, more asbestos for gaskets, more lead in the paint...

 

How about cloth wiring insulation?

 

 

 

 

Bruce Moxon

No asbestos -- there are many authentic substitutes to the problem which are better or safer. Bakelite works and worked -- there is no safety reason to mess around.

 

Lead loaded bodies -- working with lead is a serious hazard; working on lead loaded bodies is an incidental hazard, but do not spend time in the body shop.

 

Who makes authentic wiring? Cloth wiring for 1930s and some post war cars? 



#15 Terry Walker

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Posted 03 August 2014 - 03:58

Cloth wiring is certainly availablle in original colour schemes from specialistVintage suppliers. It is remanufactured, with the cloth weave over modern insulation materials, so it looks identical. Whether you could get exact perfect copies of cloth wiring is another story. 



#16 kayemod

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Posted 03 August 2014 - 08:51

I can get fibre at the boat yard. Can I get the same polys to glue it together?

 

Pretty much, I think all polyester resin is blue these days rather than a light pinky brown, but it does the same job and looks just the same when cured. Differences in resins are one of the few things we can thank EEC legislation for, the current stuff is much less smelly and generally better to use, and supposedly less of a health hazard to users. EEC interference has done similar things to paint as well, though current water-based products are in many ways inferior to the solvent-based stuff that most of us are old enough to remember



#17 Vitesse2

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Posted 03 August 2014 - 13:34

Depending on the material, sheets were usually in Standard Wire Gauge [SWG], or Birmingham Gauge [BG].......anyone know what these are in milli-bloody-metres ? :)

Birmingham Gauge to Inches and Millimetres

 

Standard Wire Gauge to Millimetres



#18 Siddley

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Posted 03 August 2014 - 13:57

 

 

I don't know how to pose a polite question. When constructing a new wishbone for a 1960s racer, which metal would you pick?  Period or contemporary?

 

A lot of the high strength grades of steel haven't changed in decades. I don't think material availability would be an issue.
There are newer steels which would allow you to use thinner sections to save a little weight, but if you are following the original design intent right down to every single dimension then I can't see the point of using them. Unless the part was known to be a bit marginal in terms of strength back in the day.

Very high carbon steels ( .6 and above let's say  ) have changed a lot, many of the older grades are no longer produced. But I can't think of any racing car applications for them - unless anyone knows better ?



#19 Doug Nye

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Posted 03 August 2014 - 14:11

When we needed to make a 1958-style Vanwall body in the closest-to-original material obtainable we had to import magnesium-elektron sheet from the US which was not, quite, to the same 18-gauge SWG thickness as the original.  But when it comes to difficulty in matching original materials, what about original finishes?  Matching paint specs can be a nightmare these days.

 

DCN



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#20 f1steveuk

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Posted 03 August 2014 - 15:14

The problem wouldn't be so much with the materials, but more the specifications then?

 

Like the threads on the nuts and bolts. Up until the mid seventies there was a myriad of different threads. Yes, I know you could replicate a thread (you can make a one off thread on a modern CNC machine), but we are discussing simply buying the items, are we not?



#21 Siddley

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Posted 03 August 2014 - 16:10

Regarding non critical fasteners what you can't buy new you could always scrounge secondhand with a bit of creativity. I remember from when I owned British bikes ( which used a motley assortment of BA, Whitworth, UNC, UNF and even Cycle thread ) there were specialist places to get the weirder threads from.

Critical fasteners, which need to be tough and fatigue resistant might take a little bit more effort to find in non metric sizes.

 



#22 Bloggsworth

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Posted 03 August 2014 - 17:06

Dural (age hardened aluminium), or Duralumin or any other of the trade names, is still available, but just by a grade specification.



#23 fbarrett

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Posted 03 August 2014 - 18:11

What would you do for tires?



#24 Mistron

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Posted 03 August 2014 - 18:27

When we needed to make a 1958-style Vanwall body in the closest-to-original material obtainable we had to import magnesium-elektron sheet from the US which was not, quite, to the same 18-gauge SWG thickness as the original.  But when it comes to difficulty in matching original materials, what about original finishes?  Matching paint specs can be a nightmare these days.

 

DCN

When one is going to wheel the body to shape, does the original thickness of the sheet really count as 'originality'?

 

Al



#25 Charlieman

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Posted 03 August 2014 - 18:56

Cloth wiring is certainly availablle in original colour schemes from specialistVintage suppliers. It is remanufactured, with the cloth weave over modern insulation materials, so it looks identical. Whether you could get exact perfect copies of cloth wiring is another story. 

That's a good example of the clever fake. The cotton braiding may be true but the insulation will be different. Even the composition of the conductors will have changed. 



#26 Charlieman

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Posted 03 August 2014 - 18:59

When one is going to wheel the body to shape, does the original thickness of the sheet really count as 'originality'?

For curved bodywork, you're right. For bulkheads or monocoques using planar forms, thickness would be significant.



#27 kayemod

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Posted 03 August 2014 - 19:07

But when it comes to difficulty in matching original materials, what about original finishes?  Matching paint specs can be a nightmare these days.

 

DCN

 

Perfectly true, as mentioned earlier paints just aren't what they used to be, better in some ways, but the almost universal change from solvent to water based is only part of it, painting techniques have changed as well.  One thing that impressed me greatly in the Schlumpf museum in Mulhouse was the way their restored cars from the 20s and 30s had been painted, almost all had been expertly brush painted, coach painted to be more exact, just as they would have been originally. The quality of finish that a skilled craftsman can achieve by this method would impress most of today's sprayers, but the effect while impressive is quite distinctive, nothing like a modern spray paint job. Racing cars from that era, pre-WW2 would almost certainly have been brush painted originally as well, but I haven't seen many restored cars that have been done that way, and where would you look for a top class coach painter today?



#28 Charlieman

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Posted 03 August 2014 - 20:10

What would you do for tires?

I'd fit tyres instead :p . They'd look like the originals but they'd be fake. There are other unavoidable Historic Compromises (Compromesso storico) such as brake/clutch linings, wiring materials, water/fuel pipes.

 

I've been thinking about springs for drum brakes. You can buy functional replacements but they are different from period examples.



#29 Siddley

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Posted 03 August 2014 - 20:17

Some spring manufacturers will make small batches to order. Small being a relative term - you may only need 8 of them for four single leaders but you'll still probably have to buy 2000  ;)



#30 Charlieman

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Posted 03 August 2014 - 20:22

...and where would you look for a top class coach painter today?

In the cafe at a bus depot amongst the bus spotters? More seriously, I'd look at equestrianism, furniture restoration, even fine art.



#31 D-Type

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Posted 03 August 2014 - 20:40

~ and where would you look for a top class coach painter today?

They say that the body repair shops in Sri Lanka are the best in the world at colour matching.  But do they spray paint or coach paint?

 

On a more serious note, I think we must allow some lassitude to restorers with the over-riding proviso that any non original spec components must not improve the performance.

 

I think I would rather see a car that is only 85% authentic racing rather than not see it racing at all as some vital component is not available..


Edited by D-Type, 03 August 2014 - 21:01.


#32 Siddley

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Posted 03 August 2014 - 20:53

My first port of call for a painter ( in the UK ) would be to ask the Sunbeam motorcycle club who their members used. The vintage Sunbeam's were famous for the quality of their coach enamelling and if a restorer can't save enough of the original finish on a component then the second best option is a top notch modern brush finish.



#33 Vitesse2

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Posted 03 August 2014 - 21:11

When one is going to wheel the body to shape, does the original thickness of the sheet really count as 'originality'?

 

Al

On most 50s cars, no. But on a Vanwall ...  ;) GAV's spirit would notice.



#34 Doug Nye

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Posted 03 August 2014 - 21:39

Nothing can 'count' as originality.  Originality to whatever date one cares to specify is an absolute. It's either original, or it's not. And NO restoration, nor any rebuild is EVER original.  Originality is by definition a condition which survives - not one that can ever be recreated once lost or obliterated. It can in some terms be 'matched'...but it will in truth never be the same.

 

DCN



#35 RogerFrench

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Posted 04 August 2014 - 03:41

Regarding non critical fasteners what you can't buy new you could always scrounge secondhand with a bit of creativity. I remember from when I owned British bikes ( which used a motley assortment of BA, Whitworth, UNC, UNF and even Cycle thread ) there were specialist places to get the weirder threads from.

Critical fasteners, which need to be tough and fatigue resistant might take a little bit more effort to find in non metric sizes.


It's still easy to get UNF and UNC (SAE) fasteners in the US, which has made my rebuildi g of a couple of Lotuses easier here in some ways than it might be back home.

BSF and Whit are a bit more of a problem, but still possible.

#36 wilga1

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Posted 04 August 2014 - 03:54

When the Porsche 917/30 Can Am car was introduced, Mark Donohue was asked what it was made of.

 

He replied "unobtainium".

 

Where does one get that now?



#37 Lee Nicolle

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Posted 04 August 2014 - 04:01

No asbestos -- there are many authentic substitutes to the problem which are better or safer. Bakelite works and worked -- there is no safety reason to mess around.

 

Lead loaded bodies -- working with lead is a serious hazard; working on lead loaded bodies is an incidental hazard, but do not spend time in the body shop.

 

Who makes authentic wiring? Cloth wiring for 1930s and some post war cars? 

Bruces comments mirrored my thoughts. But lead loading and filling of bodies is still practiced. A resto shop I know does it all the time. No more dangerous than using solder. Bog is quicker and cheaper though.



#38 Lee Nicolle

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Posted 04 August 2014 - 06:47

My first port of call for a painter ( in the UK ) would be to ask the Sunbeam motorcycle club who their members used. The vintage Sunbeam's were famous for the quality of their coach enamelling and if a restorer can't save enough of the original finish on a component then the second best option is a top notch modern brush finish.

Biggest problem is that the paint itself is different. Because of the bans on many materials [generally sensibly] you cannot get the same finish as achieved 50+ years ago. The old story of 50s and 60s laquers v modern 3 pack or eurathane paints. Better finish and even if done in laquer the colors and finish vary anyway.

Modern alloys generally are better. 

Modern wiring coated in cloth looks similar but sure is not the same!

Modern tyres are modern, even proper historic tyres.

Modern steels too are generally better. Though a tube chassis can still be nickel bronzed together as many constructors did in the day. Though reputedly it works better than it did then.

Modern bolts seldom have the same appearance of the past. Same threads and spanner sizes usually but visually different. As are modern [superior] heim joints..

Brake material is different.

 

Realistically virtually every 'replacement' material is different. Generally [though not always]  made better, or made for modern markets.

And yes the metric v imperial sizes cause so much grief. Work on an older  car, a house or building and you will have it cause you grief in every way. 



#39 LotusElise

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Posted 04 August 2014 - 15:59

The chap who I bought my Wolseley Hornet from has been known to use a brush when painting bodywork.

I'm not sure whether he works to the standard you would want, but he's not bad at it.

 

Re: metric vs imperial - not motorsport-related, but interesting nevertheless - the bath-house at Toc H near Passchendaele was designed in imperial, but built using the same metric measurements. It being wartime, there wasn't enough time or resources to re-do it, so the gigantic bath-house is still there to see.

 

The US still largely uses imperial, so import could be the way to go. Do India or China use either or both? Ordering from either place can be a nuisance, but both still have strong heavy industries.



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#40 doc knutsen

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Posted 04 August 2014 - 16:39

The problem wouldn't be so much with the materials, but more the specifications then?

 

Like the threads on the nuts and bolts. Up until the mid seventies there was a myriad of different threads. Yes, I know you could replicate a thread (you can make a one off thread on a modern CNC machine), but we are discussing simply buying the items, are we not?

 

Hm, hopefully not threads made in a lathe in any structural or otherwise critical application...



#41 doc knutsen

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Posted 04 August 2014 - 16:46

The chap who I bought my Wolseley Hornet from has been known to use a brush when painting bodywork.

I'm not sure whether he works to the standard you would want, but he's not bad at it.

 

Re: metric vs imperial - not motorsport-related, but interesting nevertheless - the bath-house at Toc H near Passchendaele was designed in imperial, but built using the same metric measurements. It being wartime, there wasn't enough time or resources to re-do it, so the gigantic bath-house is still there to see.

 

The US still largely uses imperial, so import could be the way to go. Do India or China use either or both? Ordering from either place can be a nuisance, but both still have strong heavy industries.

 

Imperial fasteners, bolts and nuts, are widely available through all the companies that carry racing spares.  MS, AN or NAS specs are superior to most nuts and bolts used in the Sixties and Seventies, though some poeple

bought fasteners from armed forces surplus stores several decades ago.



#42 La Sarthe

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Posted 04 August 2014 - 17:00

On metal specs, the answer to some extent depends on the age of the car and hence the material specs it was built from. A small part of my day job includes work on historic aircraft, including advising and approving alternative materials for the BBMF when they're doing repairs and/or rebuilds. In some cases the exact specification from WWII just isn't available anymore, and so you have to choose the closest modern equivalent  that will ensure the structural integrity of the part through its life. The same applies to metal treatments etc.

 

It's sometimes surprising what can be found, but you probably have to accept that it can never be a 100% reproduction. I'm sure it's exactly the same for cars from the 30s, 40s and 50s.



#43 Siddley

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Posted 04 August 2014 - 19:17

Hm, hopefully not threads made in a lathe in any structural or otherwise critical application...

 

That depends on the application. I wouldn't worry about a bolt loaded in shear which had lathe cut threads. Or to a certain extent any bolt which was carefully dressed afterwards to remove stress raisers and had a nice radius in the area where the thread runs out into the shank.

I used to be a gunsmith and have threaded a lot of firearm barrels to accept silencers. With a large calibre firearm the pressure inside the silencer will spike to well over 10,000 psi. This will try to pull the unit off the threads. It is extremely rare for threads to fail on barrels, I have never come across it myself. There are failure modes, but they almost always involve poor design in the silencer itself.
 



#44 Doug Nye

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Posted 04 August 2014 - 21:39

America's faith in the Imperial system has always seemed faintly ironic to me, considering how the bunch of tax-dodgers opted-out of the real one so long ago.  Apart from NASA's celebrated Mars mission cock-up with Imperial/Metric mismatch do their vehicles in fact use Imperial fixings? Please advise?

 

DCN



#45 Siddley

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Posted 04 August 2014 - 22:04

The vehicles our colonial chums would call 'domestic' use A\F fasteners, presumably everything else made there is imperial unless there is a good reason for it not to be. I ordered some knifemaking steel from the US last year and that came in an imperial size ( not that it matters much anyway when you are going to heat it up in a forge and belt seven bells out of it with a hammer and anvil )

Imperial isn't too bad a system as long as you can deal with it in decimals. The only dimensions that drive me up the wall are fractional ones - which I rarely encounter thankfully.

 

Edit :- regarding NASA, the conflict between imperial and metric units goes back a long way further than the mishap with the thrusters on that Mars probe.
Like the Apollo Guidance Computer. The astronauts, being test pilots, wanted their flight data displayed in aviation units such as feet per second, nautical miles and degrees.
The trajectory calculating boffins thought in metric units, because that was the standard for physics calculations. The poor programmers had to somehow convert one to the other inside a very primitive computer which had memory and processing power on a par with a 1980's pocket calculator. Making sure that nothing went wrong while converting decimal to octal and back to decimal and still coming up with the number they first thought of :lol:
Some tinfoil hatted conspiracy theorists claim that this is proof that the moon landings were faked. I have read an awful lot about that Apollo computer and I just claim that NASA had some very, very clever people working for them...


Edited by Siddley, 04 August 2014 - 22:26.


#46 Lee Nicolle

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Posted 05 August 2014 - 01:58

The US is another confused country. Most modern cars are made in metric in the US. but they drive in MPH. Most of their building units however are US imperial,, which is different sometimes to UK imperial. As is their US gallons which is aprox 4 litres, not the imperial 4.59. 

Why they did that would be interesting to know. bloody stupid, though so was some UK only measures.

Though metric is getting increasingly different too. In bolts for instance, metric fine, metric corse. Very occasionally with a slightly different pitch. Some smaller bolts are 7mm. Not what was accepted as 6 or 8, 10 12 etc.

A friend of mine is/ was converting Euro automotive drawings to a standard that Aussie engineers could build cars too. For GM.

 

Back to the thread, many fabricated items were and still are built to the size of steel available, or in sheet metal the size of the sheet. The metric equivilant is not quite the same, ever! If you are making a panel from a 6x4 sheet [guage is less relevant] a metric equivilant will not do the job. Or 35mm is not 1 1/2". That is yet alone the inside diameters.

 

I used to buy quality machined bright tubing for spacers, sleeves etc etc.1" to  3/4". 5/8 to 1/2" . so simple to use. Just part off the approriate length. eg 3/4" heim joint with 3/4- 1/2" Then use a half inch bolt. And to centralise [or not] the sleeve in the factory pick up use some 3/4- 1". to sleeve the 3/4.. Buying in small amounts it was not expensive and oh so simple. noone sells it now, or metric equivilant. In fact buying bright steel flat is very hard now. in metric or imperial.It was great for making brackets, spacers etc where accuracy is imperative. This is the scenario of the last 20 odd years.

 

So again. too build a true replica will be impossible. Even on something built in the 1980s!



#47 RogerFrench

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Posted 05 August 2014 - 04:38

Lee Nicolle,if 7mm was good for Bugatti, it's good for Americans too.
American Imperial is sometimes more logical than British, it seems to me. 16 fluid ounces to a pint, 16 ounces to a pound, for example.

#48 Ray Bell

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Posted 05 August 2014 - 05:47

Originally posted by Siddley
The vehicles our colonial chums would call 'domestic' use A\F fasteners, presumably everything else made there is imperial unless there is a good reason for it not to be.....


Having just crawled under and over many dozens of such beasties in wrecking yards in America, I can say this is not the case...

There are metric threads in use and there have been for some years.

#49 Ray Bell

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Posted 05 August 2014 - 05:52

Originally posted by Lee Nicolle
The US is another confused country. Most modern cars are made in metric in the US. but they drive in MPH. Most of their building units however are US imperial,, which is different sometimes to UK imperial. As is their US gallons which is aprox 4 litres, not the imperial 4.59.....


3.8 litres for US gallons, 4.546 for Imperial. There may be decimal places on the US one too, but they're not printed on the top of urinals.
 

.....Though metric is getting increasingly different too. In bolts for instance, metric fine, metric corse. Very occasionally with a slightly different pitch. Some smaller bolts are 7mm. Not what was accepted as 6 or 8, 10 12 etc.....


The problem to which you refer, or at least a large segment of the coarse/fine problem in Australia, is the Australian standards for threads. There are plenty of fine and coarse threads, for instance, for a 12mm bolt. 1mm, 1.25mm, 1.5mm, 1.75mm and even 2mm pitch. There are probably special-order items with 0.75mm pitch. But the standards here ignore most options and the one most sadly lacking for automotive use is 1.5mm... 1.75 is our standard.

As mentioned, 7mm bolts have been used in European cars for decades.

Edited by Ray Bell, 05 August 2014 - 06:02.


#50 BMH Comic

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Posted 05 August 2014 - 06:22

The good ole Metric system, good for some and not for others, you will struggle to find a metric bricklayer though, the brick is 9" long and 4 1/2 " wide by 3" tall everywhere on the planet with a 3/8" perp joint.

 

Just try doing it with 10mm joints and see what happens, exponentially you end up with a very silly odd number when you get to 27 bricks high. Half a brick is a no brainer even for the simplest people, its a brick width.

 

My dear mother explained it as a youngan that the imperial system lent itself to easy division for halves, quarters eights and sixteenth even thirds and sixths easy enough and no better example than laying bricks, half a foot is no different, half of 308.4mm is all a bit hard, six inches much better and a 3 inches for a quarter, even the metric foot is a problem, half is easy enough  but 1/4 isn't a whole number, same with bolt sizes and metal gauge, if it can not be calculated in your head you end up with what every machine shop now has, a pocket calculator. A whole new business just to do the maths we could all do in our head.