Why is the world of model engineering still imperial?

Goodness me, eight pages of postings. Well, proved myself to be as guilty as the rest of you thinking this is interesting.

But I am intrigued by the thought that a youngster raised in metric will find the use of imperial to be a barrier. Do we really think that? Mmm, I don't know.

I, like most all of you, switch between imperial and metric and enjoy the flexibility it brings. My eldest and youngest sons, who are 39 and 33 years old respectively, happily talk to me in both measurements; one is a builder the other a design engineer. They did not use imperial at school. So does youngster mean under 25 years old?

If you are going to build a model locomotive there are massive learnings to do with machining, materials, soldering, painting. etc. Is the measurement system going to stop you? Well, yes if you just don't want to go there.

Many of us think that scratch building a 5" steam loco is an interest that is dwindling anyway, never mind the measurement units.

Norm

The US pint contains 16 fluid ounces I.e. 1 lb of water, which does at least seem more consistent than the Imperial version.

Rod

Isn’t that a volume measure?

No. A scruple is equal to 20 grains a measurement of weight/mass used by Apothecaries.

CS

Definition now I’ve looked it up is it can be fluid volume or weight. Another nail in the coffin.

There is an apothecary measure defined by the amount of dry substance such as chopped herb you can pick up between thumb and forefinger but I’m blowed if I can remember the name. It was remarked on by Steven Maturin in one of the Aubrey/Maturin novels by Patrick O’Brien.

regards Martin

Pinch? (= 2 smidgens)

dave.

No I’m sure it was less obvious than that, Steven had finally got one over on Jack Aubrey for all his naval terminology so it was definitely something obscure.

regards Martin

You may find it here, Martin **LINK**

https://en.wikipedia.org/wiki/Approximate_measures

… or it might be really obscure !!

MichaelG.

Oh it’s definitely really obscure. I remember at the time I must learn that word but have since forgotten as you do with anything you don’t use.

I will find it eventually as I read all 20 books every 2 or 3 years.

regards Martin

Me too!

Rod

Yes Norm, eight pages and would be a darned sight less if we could refer to a post # rather than cut and paste vast lines of text.

Sorry Jason, my ref to 1/8"- 0.312 Should have been 1/8" OR 0.312 (0.3125 if working for NASA which many think they are).

Unfortunately the designs that the O/P seems to favour are 'Old school'. Yes, there are metric designed models but are precisely that and not 'Conversions'. Years ago, I had a hard time trying to convince an American colleague that an unimportant dimension of 25mm didn't mean he had to cleave 0.4mm OR 16 thou from a 1" bar of metal.

Regards Ian.

But an 1/8" is not 0.312, should it have read 5/16" or 0.312" = 7.9375mm.

Edited By JasonB on 09/03/2023 11:49:07

A good answer from Jelly, who's understanding of Imperial goes some way under the waterline! I suspect his list is more comprehensive that most. Slugs are in there, so perhaps I was wrong to assume Harry Wilkes youngsters must be extra smart to know about them! Personally I find slugs, blobs, pounds (two meanings!), poundals and pounds-force confusing, as was the painful way the metric system got to it's present relative clarity!

But there's much more to Imperial than Jelly's overview. Drilling into Energy, Work and Power, in addition to lb*ft and BTU, there's the Therm and calorific value in BTU per cubic foot. Temperature is measured in Fahrenheit. The Mechanical Equivalent of heat is 772 foot-lbs, and one Horse Power is 33000 foot-pounds per minute (550 ft-lbs per second). So if 1lb of coal of heat value 15,000 BTU delivers about 12,000,000 ft-lbs per hour, which is 200,000 ft-lbs per minute, or 6.06HP. 6.06HP doesn't mean much to an electrician, but all we have to do is multiply by 745.7 to get the answer in watts (4518.942) This system caused trouble from the outset, because the scientists who determine fundamentals like calorific values, specific heats, and other basics always work in metric, making it necessary to answer questions like:

How many calories are equivalent a therm? (1lb = 453.6g. 1 cubic foot = 28,317cc)

and

How much energy, in foot tons, is given out when 1lb of steam condenses? (1lb liberates 965BTU).

Even more awkward arithmetic needed if the answer is needed in inch ounces, another valid imperial unit:

The problem is the number of conversions generated by illogical relationships within Imperial measure. 'Magic numbers' are constantly required: 33000, 772, 550, 745.7 mentioned above, and many others. There are 231 cubic inches in a gallon, but is that a US or a UK gallon? 1728 cubic inches in a cubic foot. 46656 cubic inches in a cubic yard. How many feet per second is 1 mph?

Hard to understand why anyone defends this system, look at the detail and it's a mess!

Dave

Dave,

Just accept it, belief in the Imperial system is like a religion, not open to rational argument. In your moderational capacity you'd better close this down before the howls of protest.

Edited By duncan webster on 09/03/2023 14:00:54

How does an Imperial howl compare to a metric moan?

Hogsheads/metre/nano-fortnight anyone?

Furlong firkin fortnight (Google it) is well established.

Edited By duncan webster on 09/03/2023 15:14:42

Edited By duncan webster on 09/03/2023 15:20:58

Jason, DOH! that's another half brain cell that died without me realising. 1/8" OR 0.125 or 3.175mm

Regards Ian

That's an excellent example of why you should avoid converting, and work in what you're given. Although the insistence of having both fractions and decimals on the same part is tiresome. I've yet to see a machine dial marked in fractions.

The maths that links the various measurement system is still the same but working out the units becomes the main problem. Pressure is force per unit area whether it is Newtons per square metre or tons per acre! However the metric system is still complicated by using a short hand that separates the user from the units such as using the term Pascal to mean Newtons per square metre.

The main problem I have is that the Imperial system, which probably has its origins in France due to 1066 and all that, has a variable number base. So a ton is 20 hundred weight and a hundred weight is 112 pounds which is 16 ounces. However a tonne is simply a 1000kg or 1,000,000 grams. So one can simply move the decimal point depending on what size of engineering one is trying to compute.

I believe Napoleon instigated the adoption of the metric system because of lack of standardisation of weights and measures in France and the opportunity this gave traders with less scruples to confuse or even swindle their customers.

This may still be the case in the UK where my gas bill states the units I've used, converts this to BTU's and then kW/hrs. I'm OK with this but there will be some who will be confused.

CS