Imperial v Metric Measures

[mark costello 1Participant @markcostello1]

I don't think We missed Mars, just center punched it a bit.

[Howard LewisParticipant @howardlewis46836]

Martin, Imperial measurements and hardware are not the sole province of the model engineer.

Preservationists in Railway, Traction Engines, Road Vehicles, and Industrial Archeology need Imperial measurements and hardware.

Indeed there may well be some machines in industry which still produce precise work despite containing "Archaic" fasteners and dimensions.

For a given situation, each system has advantages over the other.

As in everything, the horse has to be suitable for the course.

Howard

[DMBParticipant @dmb]

Wow! Look what I've achieved, ha, ha. Less than 24 hours and nearly 3 pages of arguments. Imp/Metric is like religion and a few other subjects that just run and run.

Having taken the P , I can say that I try to use what I'm given. Almost finished building Harold Hall's grinding jig for which the drawings were in metric. I enjoyed the journey as metric is so easy to use due to its decimal base rather than the medieval duo-decimal rubbish. If I am confronted with Imperial drawings, that's OK in that I was taught that at school to start with and metric later. Result is I can still visualise Imperial measurements that come so naturally from schooldays. Still prefer to multiply or divide in 10ths, metric. HH is one of the better model engineering designers who got it right whereas some have made drawing errors all over the place. Just one problem – sourcing small quantities of his specified material sizes. If necessary I can easily convert small dimensions from one system to the other, just using the calculator between my ears, not difficult. E.g., 19mm to .748", done in head. Real calculator says .7480314" I picked 19mm as a purely random size to convert. Obviously, I would much rather use one or other rather than flitting to and fro with the risk of errors.

My original points were that different milk suppliers placed emphasis on one or other system, no consistency. Conversions looked odd but admittedly I didn't think about American versions being slightly different. The other point about Chains or for that matter, Cables, Fathoms and lots of other ancient measurements really should be scrapped.

[Mike PooleParticipant @mikepoole82104]

Reading through this thread I have noticed a number of mistakes which are probably typos but if they were to reach the shop floor they would result in some unexpected products. Maybe it highlights the problems of converting between systems.

Mike

[Michael GilliganParticipant @michaelgilligan61133]

< pedant alert >

‘Metric’ and ‘Decimal’ are not the same thing.

MichaelG.

[Anonymous]

Posted by Mike Poole on 09/04/2022 21:40:27:

…highlights the problems of converting between systems…

Could be that people are unable to do basic arithmetic?

Andrew

[duncan webster 1Participant @duncanwebster1]

Like NASA? They managed to crash a spacecraft by mixing units oops. I'm old and bi-lingual , but metric is best

[DMBParticipant @dmb]

Mike Poole,

That's precisely why I said that I try to use what I'm given, e.g., HH supplied his tool grinding jig drawings in metric in his book. So I used metric. Could only source some steel sections in Impreial, so I treated them as peculiar sized metric so all was in same system!

Andrew,

Basic arithmetic is my specialty, I think! In the example that I gave, 19mm, double it and again, so we have .760" I find it much easier for head calcs., to do it rather unconventionally, like next stage is having got to .760" on the assumption that 1mm = 40 thou, it's necessary to correct the 'error' being the difference between .039375 and .040000, which is 5/8 per mm , so 5 X 19 = 95, ÷ 8 = very nearly 12(thou) to deduct from .760" = .748", answer damn close to correct figure. Told you it's very unconvential and spelling it out above in minute detail seems long winded but I get there very quickly and it works very well.

Michael Gilligan,

I accept your comment but point is, multiplying/dividing by ten to calculate metric quantities is easy but impossible to match in Imperial, which is what I meant.

[DMBParticipant @dmb]

Duncan,

I know about the yanks balls-up. That's why I try hard to use what I'm given, be it Imperial drawing or a metric one. Rules and Verniers have both systems side by side so not difficult.

[Frank GorseParticipant @frankgorse]

The cable is one tenth of a nautical mile so should be decimal enough for most people. The nautical mile is one of the few units that has a sensible derivation,it’s the length of a minute of latitude plotted on a standard navigational chart so distances can be measured with the simplest equipment,dividers. Not so with kilometres.

Fathoms haven’t been used here for many years but are still in use in the USA. If you want to tell the Americans they’ve got to stop using all these archaic units,good luck! Wars have been started over less.

[Anonymous]

Posted by DMB on 09/04/2022 22:16:17:

Basic arithmetic is my specialty…..

I was thinking more of equating 30mm with 1 foot, an order of magnitude out.

For the example given I happen to know that 19.05mm is exactly 0.75", so just subtract 2 thou. Depending upon what I am doing I tend to work in imperial or metric, so rarely need to convert, at least to any degree of accuracy. If I do, it is done beforehand in the planning stage and written on the drawing.

Andrew

[DMBParticipant @dmb]

As another example of quick easy calcs in the head, I was at the club one day with a group who were discussing construction of something and they had a mix of measurements like say, 16G sheet to be fixed to some 3mm thick angle and another piece which was say 5/32" thick and the chap doing the measuring and alking started floundering. I quickly reduced everything to Imperial decimals, I called 16 G .0625" as it's close to 1/16", 3mm became .120" less error approx. 2 thou, so .118", 3/32 = .09375, total .27425" Got there so quick, the Tornado simulator service engineer standing near me was shocked, wanted to know how I managed it so quick. If the calc answer is important to be correct, I will still work it out in my head for fun but use a calculator just to make sure of no mistake. I have been wrong, occasionally.

[DMBParticipant @dmb]

Wow, page 4 now, getting late, going 2 bed.

[Michael GilliganParticipant @michaelgilligan61133]

Slight digression ….

Some might have noticed that I mentioned, in a recent thread, a ‘sandwich panel’ made from Aluminium alloy plates and a honeycomb core.

I had a bright young chap, fresh from University, assisting me and he kindly estimated what the first ‘free-free’ resonant frequency should be: His answer was about 4Hz … So I asked him to prop it up against the wall and check how much it sagged

We then tested it, and [as hoped] the frequency was about 400Hz

His calculations had, of course, involved working with the non-intuitive unit of gigapascal [the pascal being a ludicrously small base unit in this application] and he had lost count of his zeroes.

MichaelG.

[Sam StonesParticipant @samstones42903]

Not so much Imperial versus Metric …

My guess is that this (five to ten-minute), well-circulated story of horses and asses might already have appeared in the ME forum …

**LINK**

Sam

[Anonymous]

Posted by duncan webster on 09/04/2022 22:01:42:

Like NASA? They managed to crash a spacecraft by mixing units oops.

Not to mention Air Canada's Gimli Glider

[DMBParticipant @dmb]

I avoid exact long division in the head as being one step too far and use multiplication/comparison instead. Well, it works very well for me. Take the previously mentioned 700m/2300ft. From 700m, it's 700yds + another 10%, 70, total 770, which is easy to multiply by 3 arriving at 2300. But, the other way, I can see that 2300 divided by 3 is 700 + the approximate 10% difference between metres and yards, amounts to 2310. Near, so now guess a round 2300.

I have used small sizes approximations so often that I can remember quite a few without having to calculate every time, like 17mm is around 11/16". I do often consult drill tables to ascertain exact next larger size tapping drill, e.g.

[Anthony KendallParticipant @anthonykendall53479]

Posted by Nigel Graham 2 on 08/04/2022 23:30:09:

The cm is not a "Preferred Unit" – as engineers we all know it should be metres and millimetres except in a few specific applications. Why? 'Cos the ISO says so. Though I don't condone it – mathematical neatness does not always make for day-to-day practicality.

I have another reason for not using cm, but cannot explain why.
I find/found when I used cm I made more errors than when using just mm and m. Just like that for me.

We seem always to arrive at a midway no-mans land – only half changed over. No matter how hard we all try to go totally metric – it seems to be impossible and we have to convert between systems.

They said go centigrade (now called Celsius), and I did, and got used to it and it became natural. Then F still appears and I have to convert.

[CirclipParticipant @circlip]

in skools, cms are taught cos you only have five digits on each hand, 100mm would cause a brainstorm. But for 100mm in inches, you only need one hand with one digit spare.

Regards Ian.

[DMBParticipant @dmb]

School science lessons, we used "Celsius" except when mentioning "Centigrade Heat Units". How daft can it get?

Taught decimetres but they seem to have fallen by the wayside as never see them mentioned anywhere.

Whilst I think there is some merit in keeping the number of different measuring sizes to a minimum, I think that mm, cm and metres could be used in a sort of prortional way. Vehicles being big objects, why not quote length as say, 19.8m and a person's height as 180cm. Kitchen worktops 60cm but say 50mm thick.

Cross sections of most things could be in mm, except when they get much bigger like diameter of a large tree trunk in cm.

All much better than yds., ft., ins., with the cock-eyed quantities of units making up the next larger unit.

As I've previously stated, I try to work with what I'm given on a drawing. If drawing is metric, use metric sized materials where possible and if necessary, convert an Imperial sized piece to metric before using it. All helps to avoid errors and makes life simpler.

Likewise, with Imperial drawings, use Imperial materials as far as possible and convert an odd piece of metric material to Imperial size before using it.

When I started constructing HH's t&c jig, I couldn't source the specified metric sized pieces of steel in the small lengths required. Our usual suppliers didn't seem to stock what I wanted but Joe at Maccmodels came up trumps with some and another poster on here suggested a business in Hampshire, does traction engine stuff, but cannot remember their name. Sods law operating, I will remember immediately after I add this post! I think things are starting to improve, possibly due to an increase in demand for metric materials.

[V8EngParticipant @v8eng]

I think people need to be taught Centimetres in schools because they will find them in everyday life.

Oddities appear to occur, for instance the fitting instructions for a (German) hob in our kitchen show the main dimensions in mm but the heat plate sections are shown as diameter in cm.

Edited By V8Eng on 11/04/2022 11:12:50

[SillyOldDufferModerator @sillyoldduffer]

I say Imperial Measure is a damaging obstacle to progress. Yesterday's men sticking to a system they think they understand is one thing, but selfishly foisting it on future generations is irresponsible. That we personally have a feel for feet, pounds and Fahrenheit doesn't make it a good system. Look deeper into FPS and it's obviously unhelpful for science and engineering.

If anyone thinks FPS is OK, look up Furlong, Firkin, Fortnight. FFF is obviously daft because no-one is familiar with the units, but Imperial and FFF are the same system. If you see FFF is bad, then Imperial fails the same test. Both are bad systems. Though imperfect, MKS (SI / Metric) is better because it's more consistent.

Despite all the arguments trotted out in support of Imperial, the rest of the world shows absolutely no interest in adopting it.

Dave

[DMBParticipant @dmb]

I am an old codger, iif you like, but at no time have I praised up Imperial v Metric. Just that I passed through school being taught both systems so I can now happily use either or a mix of both.

However, I think that it's more than time for a complete changeover and join the rest or at least, most, of the world. The other Luddite countries will have to get aroundtoit sooner or later.

If there was a complete change, then far less time would be wasted teaching the obsolescent Imperial system and at the same time make it illegal to quote conversions on milk bottles or saucepans or anything else.

[KWILParticipant @kwil]

V8Eng & DMB

Vehicle drawings and Jigs "always" use mm so logical to give vehicle size in mm.

Hobs manufactered in mm and as regards the heat plates in cm, because saucepans "always" sold in cm sizes.

Yesterday I was watching on Utube, my favourate "Tally Ho" [Sampson Boat] Episode 123, the rebuilding of an old English Gaff Cutter

Keel attachment bolts 1 1/4" thread diameter aluminium bronze, holes 1 1/4", actual bolts 1 15/64" to give clearance Keel weighs in at 9 tons.

Anyway why fuss about Metric vs Imperial? Just use what suits you for the job in hand.

[duncan webster 1Participant @duncanwebster1]

Posted by Frank Gorse on 09/04/2022 22:22:49:

The cable is one tenth of a nautical mile so should be decimal enough for most people. The nautical mile is one of the few units that has a sensible derivation,it’s the length of a minute of latitude plotted on a standard navigational chart so distances can be measured with the simplest equipment,dividers. Not so with kilometres.

Fathoms haven’t been used here for many years but are still in use in the USA. If you want to tell the Americans they’ve got to stop using all these archaic units,good luck! Wars have been started over less.

Not a lot of use for east/west measurements, as the lines of longitude get closer together as you move away from the equator. USA science has already dropped Imperial, the rest will follow sooner or later

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