Why is the world of model engineering still imperial?

My Dad was an aerospace design engineer who worked on everything from homebuilts to air launched weapons and satellites . He told me that he occasionally worked in a unit he called an elephant . Eg; If dimension A is 1 elephant then dimension B must be 2 elephant , dimension C becomes 1/2 an elephant and so on. The point of course being that the dimensions were all relative , so for the purposes of determining a general shape and layout an elephant would do the job.

Clive, agree on wretched gas meters. I'm also OK with ability to convert reading to KWH, but why should I have to? I think that all future gas meters due for renewal, should only be calibrated in KWH, to make life easier for all. I expect someone will say, ah yet but calorific value changes or some other silly excuse. Let the supply co. struggle with that one - could be averaged. Surely the variables cannot be so wildly variable? I dont actually bother with the exact conversion, I'm happy to multiply by 31 to just get a ball park estimate.

As regards M/I, it's best to only work in your chosen system and not try to convert. If you do, there is a huge risk of introducing errors. Take loco drawings from the past, all my machinery is calibrated the same - Imp. so that's what I use to say machine a wheel or cylinder casting. I only have to do a shopping list of steel sections or brass bar, e.g., still available. If I have a set of metric drawings, like say Harold Hall's, then I have obtained metric sized metals to suit, wherever feasible. As regards drills and threads, same applies - I used M drills and taps for HH's designs and I'm  using the other motley collection of frac/nos./letters drills and all the diff. threads t&d to complete my Sweet Pea loco.

John

Edited By DMB on 10/03/2023 10:32:04

Why do you need to covert your gas bill readings. I only ever use them to compare what I used this quarter with the same quarter last year. So long as they are the same units elephants will do as Lee Roger’s has said.

Carpenters and Joiners often used what was termed a story stick. Simply a suitable length of wood which would be marked out with the pertinent dimensions of the job. So if for example a dresser was require to sit between a room corner and a fireplace everything was recorded on the stick marked off from the room. So when the dresser came to be made its story stick could be constructed with direct reference to the room stick. No measurements or units to get wrong just a series of marks along a length of wood. It’s an element and simple use of gauges really.

regards Martin

I've heard of the elephants unit from Americans describing sink holes... The tagline being, "Americans really will use anything to avoid using the metric system"!

I seem to remember another instance using washing machines...

Edited By UncouthJ on 10/03/2023 11:14:12

Bit of trivia, but Gas Suppliers have been required to charge for the energy their gas supplied when burnt, rather than the volume delivered, since the Gas Regulation Act (1920).

Gas was originally supplied for lighting, not warming the house or cooking, and it was a great improvement over tallow wicks, candles, and oil-lamps, even when burned in a plain mantel.

People valued gas for it's ability to burn with a bright yellow flame, not it's heat value. Hence gas meters measured volume, in cubic feet. Later, gas was used to heat water in bathrooms and kitchens, to warm homes with gas-fires, and as a source of industrial heat. Also, incandescent gas mantels had been developed: these produce a bright white light from being heated, and are poisoned by the chemicals in gas that produce the yellow flame so valued by early Victorians. Plus gaslight was being supplanted by electric light, which was cooler, brighter, and more convenient. As usual the small-c conservatives of the day resisted all change to the best of their ability, so it took over 25 years to make the switch from measuring volume to heat value.

When it finally happened there was a kerfuffle when gas bills charged 10d per therm rather than the good old 3s 11½d per thousand cubic feet everyone was used to, and obviously the old ways are the best.

Another amusing example of people objecting strongly to replacing an out-dated system they thought they understood, but didn't. Didn't matter the new waywas simpler and far more informative, because everyone hates change! Even me.

And here we are again, 57 years after metrication, UK gas bills are still confusing! And the change could have been made in 1920, because engineers and scientists understood therms and kwh long before then.

By the by, a US Therm and British Therm are both 100,000 British Thermal Units, except a British Therm is smaller, a mere 0.99976 US Therms. Something to do with National one-upmanship I expect, big countries need bigger Therms!

Dave

My one annoyance with the SI system is the use of names like Newton and Pascal. I think parameters should be expressed in their fundimental units. For example the units of force would be kg.m/s^2 (it would be nice to have a superscript font).

One has to suspect some form of nationalism here. Perhaps it will end when a parameter is named after Santos, the great Andorran physicist.

JA

Edited By JA on 10/03/2023 12:10:02

JA

I agree with your frustration of using the shorthand notation of say Newtons and Pascal. It is bad enough being asked to set my altimeter to 1013 hectopascal rather than the earlier mbar so heaven forbid if they used the fundamental units.

CS

Hecto is 10^2, so not an approved SI multiplier, Who dreamed that one up I don't know. If you were a SI purist it would be 101.3 kiloPascals, but 1 bar is 10^5 Pascals, allowed because it's near enough one atmosphere, normal divider is 10^3, so millibar

Edited By duncan webster on 10/03/2023 14:47:51

Having enjoyed giving Imperial measure a well-deserved thrashing, I have to admit MKS isn't perfect either!

The original centimetre-gram-second version (CGS) was consistent, but its base units generated inconveniently big numbers. Easier to calculate in than Imperial, but clunky for many practical calculations, and the scale doesn't feel right.

Metre-Kilogram-Second eliminated the worst of the clunkiness, but not entirely. Calculations involving pressure always upset me because 1Pa is tiny, 1N per square metre, and there are other examples! At least 1hPa = 1mbar, and not some weird ratio, but I'm still not used to it!

We don't have a perfect system of units, it just that metric is considerably less bad than the alternatives!

Dave

And of course some areas of science use more convenient units like the Angstrom and the electronVolt.

regards Martin

PS there are probably others but these come to mind.

Use which ever system is appropriate for the job in hand.

I wouldn't want to work in Imperial on a Metric machine, or vice versa, . Probably spend more time using a calculator than cutting metal.

Having worked for a company where EVERYTHING had to be Metric, it was ridiculous working with drawings where the dimensions were partial mm, when then original was to Imperail dimensions.

But all the original Unified threads were still specified, complete with Imperial Across Flats hexagons!

I think it's called standardisation.

Howard

JA m/s² m³

Martin C

As we seem to be swapping anecdotes rather than opinions (and thus in a much more congenial place), how about metric deep groove ball bearings (ie those with external dimensions in metric units - e.g. 6207 for a 35mm bore)?

Yes, the ball dimensions are all inch sizes (or fractions thereof).

Go figure, as they say....

/J

I am trying to understand the above. Please, no one, DO NOT explain unless you are going to tell me how to put superscript and subscript in to a posting.

JA

We don't use the SI system, it still common to see cc, ml litre etc rather than dm&sup2.

We don't use the SI system, it still common to see cc, ml litre etc rather than dm²..

A few years ago B & Q were selling threaded items quoting sizes in mm and fractions of an inch, confusingly whereas most items were metric threads some were unified.

Edited By Keith Wyles on 10/03/2023 18:05:21

For a longer explanation google superscript HTML, but try "<sup>2</Sup>"
It doesn't seem that long ago that I had to entre printer codes to achieve such things

Rather like democracy, then!

/J

I once did a bricklaying course and remember a story rod was made with all the openings to be built into the wall marked on it, it ensured that the courses could be adjusted to avoid cutting bricks. A perp lining up with the edge of an opening was also to be avoided so starting with a header or stretcher was also determined. The bricks were also measured by averaging a pile of 10. A good bricklayer will know where every brick is going before he lays a brick and the thickness of the mortar.

Mike

Edited By Mike Poole on 10/03/2023 19:07:24

I think those hex drive kits are still 1/4"