Why is the world of model engineering still imperial?

My favourites and still very useful are chains

Makes furlongs and acres easier to picture

I believe that some "metric" ball races use Imperial sized balls and don't mention the issue of screw threads!

Most weighing devices are force balances rather than mass balances as they are relatively easy to make and more compact than a true balance. Unfortunately the wrong terms are often used by lay people so the "weight" used on the old style grocers "Scales" which is actually a balance is actually a reference mass. The later Grocers "scales" were a force balance where a spring extension measured on a scale indicated the weight being measured. Most precision laboratory scales are force balances where a current flowing in a coil of wire within a magnetic field produces a balancing force to the item being "weighed". These devices use a reference mass to periodically calibrate the "balance" to account for the local gravity and variations due to the Moon which is noticeable if you are measuring to 1 part in 10 million.

Other weighing devices such as kitchen and bathroom scales use a spring in the form of a strain gauge.

CS

It doesn't matter, When the item has been made no one knows wether you used chains or microns. The fact the drawing used a set of numbers relating to imperial or metric systems only the drawing reader needs to know so they can interpret it to create the part. Converting between the two is simple enough for most engineers, it is just a number. Threads can be converted between the two quite easily, some special threads need a little thought as to why it is used before coming up with an alternative. Just for the record i am mainly metric, but use imperial for when connections are required to purchased pipe fittings.

My point about spring balances and scales that rely on spring extension is that they rely on 2 readings. One with a known mass to calibrate the spring extension and a second with an unknown mass to make the comparison. The equations are the same as the balance beam and providing the device is in the same location as it was calibrated everything cancels except mass and length. Therefor they are mass comparators irrespective of what units you paint on the scale or the standard mass. Of course once you know the mass the weight under the same gravity is in the same ratio.

I know I’m splitting hairs but that’s where this discussion has gone. If there is no gravity term in the equations then you aren’t measuring weight.

regards Martin

Not at all, it's a complicated subject deserving attention, even if we have our ideas rejected!

Standardisation of Weights & Measures has a long and difficult history. A story of order versus chaos, conservatism vs progress, practical vs theory, me vs us, local vs national, and national vs international. And a potent symbol of who is in power, which is why ambitious politicians fostered the impression that Metric was foisted on Brits by the EU. A fib.

It was recognised early that different measurement systems are an obstacle to trade. In medieval times ordering a 'yard' of cloth caused short-changing or over-provision because the suppliers yard was different. The differences were exploited ruthlessly by dishonest traders.

Imperial is the result of many painful rationalisations over centuries. They often had to be enforced by the King sending the boys round to 'explain' the need for change, and the conversation often ended in violence.

A tailor trading in Truro sees no advantage in dumping great-grandad's yard, which works perfectly well for him, and he's not going to cooperate just because the whole country poorer as a result as a result of trade problems. Not a problem in Truro that Baltic merchants can't trust English cloth measure, so our tailor resists. He calls on tradition, politics, propaganda, and deploys fear, uncertainty and doubt to delay and prevent change. His motives are personal and local, and ignore wider benefits that don't apply directly to him.

Imperial as we know it is a product of 19th Century efforts to deal with the Industrial Revolution struggling due to duff weights and measure. To reduce bother, they built on traditional foundations. The root was the yard, pound, and second, heavily embellished with hundreds of size units, related by odd ratios determined in the past. So we have grains, drams, ounces, pounds, stone, hundredweights, and tons, and the ratios are inconsistent, so although a dram is 1/16th of an ounce, there are 27.34375 grains in a dram. There are 16 ounces in a pound, 14lbs in a stone, 7.142857 stones in a Hundredweight, and 20cwt in a ton. Length measure also has many multi-ratio relationships.

Fairly obviously I hope, these conversions complicate Imperial calculations. Just because the resulting confusion may not apply to us individually (in our local home workshop), does not mean everyone is well-served by Imperial - far from it.

The big trouble with Imperial starts when derived units are needed. In mechanics these are: Energy, Force, Frequency, Power, and Pressure. Although man-in-shed engineering rarely calculates in them, they are fundamentally important to anything other than basic engineering design. Inches and thou are fine when building a steam locomotive to a plan, because deciding how strong the boiler needs to be to operate safely at a given pressure was done by someone else, a mathematically trained engineer. I worry about him because although the maths can be done in Imperial measure, it's hard work. Imperial measure is a poor tool for advanced work in science and engineering. It's odd that some model engineers deliberately favour a poor tool!

Whilst Victorian legislators were corralling Britain's chaotic traditional measures into Imperial for commercial reasons, the scientists had gone a step further. They had realised a century before that it was feasible to design a coherent system of weight and measures. (Mostly coherent - it can't be perfect.) That is, a system where units are logically related, and there are no random ratios between them. The system supports domestic needs whilst greatly simplifying difficult calculations. Not a cosy change; a coherent system requires most historic measures to be abandoned, and this trampled on the delicate feelings of traditionalists and everyone who had painfully learned to calculate in Imperial! Old dogs don't like learning new tricks. So there was an immediate, powerful reaction against metric, derided as 'foreign' by British vested interests, even though British brains were in the forefront of the new system.

Personally, I think it's a mistake to mix politics, emotion, tradition with engineering and science. When a better tool becomes available, engineers should use it. Essential in brutally competitive manufacturing. Chaps who held the firm back by insisting on Whitworth, Imperial measure, old-fashioned methods, and Spanish practices, thought small-c conservatism made their lives easier: actually, it was one of the reasons that so many 'solid' British engineering companies went to the wall.

Lesson learned - don't lumber future engineers with inferior methods just because they happen to suit me.

In my humble opinion, Imperial has been a dead-weight for well over a century. Like smoking tobacco, people love it, but the habit is harmful. So, are you a Truro Tailor or a thrusting industrialist planning for 2030 and beyond? Does anyone really believe Imperial measure will be an asset to British engineering when we are all dead?

Dave

So why are they not called Massing Scales or are there a few here who call them that rather than weighing scales and I bet you all weigh in your scrap metal.

No "M" on the weights from my balance scale either

It’s not what it’s called it’s what it DO.

I did say I was splitting hairs but such is subtlety.

regards Martin

"you have to remember that it is cold in the workshop at the moment and all the members are sat in front of the fire with nothing better to do."

True, me included I'm really excited to get started but its been below 5 deg C out there its all i can do to stare at it and oil the bed etc.

"Model engineering is imperial because 99% of drawings are done in imperial, we all bought mics verniers etc years ago when they were imperial,"

Also largely true, but for people like me not so, I've just bought a new micrometer and DTI, kit I could not have dreamed of owning when i was last machining stuff over 40 years ago on my old mans lathe at my parents home, thankfully being mostly digital it can do both, although i do have a traditional 'one trick pony' digital micrometer as well!

Because my Grandfathers stuff I inherited in 1969are still used and very useful. 😄😁

Of course you are because you are measuring a force due to gravity. Remove the gravity and the device doesn't work.

To answer the thread question, my answer is that perhaps many of the popular designs are still in Imperial.

I work in both, metric mill, imperial lathe. My apprenticeship was generally also a mixture of both, I convert using a calculator, not having a DRO.

One thing I always have an issue with is that new people coming into this "hobby" need to realise that there are critical dimensions in some components and less critical dimensions in others. Many waste time in ensuring, for example, that the base plate of a model engine has to be exactly the dimension on the drawing....it could be 1/8inch longer or 3.175 mm and no one would notice !

The elephant in the room though is getting new blood into our hobby, I am sure many are put off by imperial measurements. I guess as us old duffers eventually keel over with our hands around a 0 to 1 inch imperial micrometer, imperial units in model engineering like us will eventually wither and die...

The important thing is to get in the workshop and make stuff, either in metric or imperial, who cares !

Regards to all

Derek

I think the Imperial plans sets are going to be around long after any of us has been "re-allocated" to the next world with our favourite six-inch by sixty-fourths rule in our boiler-suit pocket.

Yet with CAD now, how feasible would it be for the publishers to scan those drawings and re-dimension them to mm? And while at it, verifying the drawing's fitting accuracy?

If so it ought also be possible to tidy them into rational sets with a lot of the details parts on A4 sheets, rather than the haphazard all-on-one typical of so many? It was done to reduce the amount of big sheets of paper needed but would the economics now favour such revision?

One possible route there is to sell the prints that need be big (the GA, and large components) but offer the smaller A4 sheet drawings on-line for the buyer to print at home. (A3 too though fewer home users are likely to have A3 printers.)

I don't know - I cannot do it but that does not mean it cannot be done! I can't swim either, but many do.

'

I don't know if some newcomers are put off by Imperial measures they have not been taught. Yet neither do most of them know a headstock from a tailstock or Walschaert's from Stephenson's, till they start to learn their way around it.

I think more importantly is if they have grasped any appreciation of actually making something rather than just buying it. Though that will go against realising the baseplate can be three-and-a-bit mm overlong but the cylinder and piston must match.. Treads carefully, lest one awakes Fafnir the Dragon, Guardian of the Accursed Ring... Gauge.

I recall some ten years ago a man gazing at my society's club locomotive, a Ken Swan version of the Kerr Stuart 'Wren', in steam at a public event. He was impressed, and asked about availability of parts and "spares" - perhaps thinking it preserved but factory-built. I replied that apart from a few fittings we'd have to make them. just as our club had built the whole engine in the last several years. I think he did believe me, but found the concept very hard to grasp!

I fear more the effect of rush on patience. Everything it seems, must be quick, instant, available with minimum physical and mental effort. Send a txt msg - moan if no immediate reply. Buy a radio-controlled model lorry, say, on-line and you don't even need leave home to collect it almost ready to run. Build the same model from scratch... that is hours of work even if substantially quicker than a similarly-sized miniature steam locomotive - and it needs practical skills and appropriate tools, albeit fewer and simpler than the loco calls for. Is commitment to any leisure pursuit now becoming a rarity?

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There are optimistic signs, but we of the Sage Age must realise that model-engineering is model-engineering and the youngsters coming along will know engineering in mm and Newtons rather than inches and foot-pounds. So it is for us to encourage them in their way into engineering, before we are sent to measure Infinity with our six-inch rules.

Maybe they can teach some of us a thing or two about modern engineering!

Edited By Nigel Graham 2 on 07/03/2023 22:05:17

That’s not really valid as my reason for posting was the contention that the general public don’t measure mass as it is difficult. In the absence of gravity constant acceleration will do just as well. Just not for Joe Public.

regards Martin

A mass balance will work just fine in reduced gravity, a spring balance won't. Neither will work in zero gravity.

One thing i hope we can all agree on is on the matter of fixings...... ( ducks for cover)

Imperial fixings are way over complicated~ how many thread standards?

Metric is sooo much simpler, i don't even have to consult a chart for the right tapping drill.

If you are of a certain age your grandfather / father (in those days of thrift) used to keep a tin of 'saved' nuts & bolts in the shed/garage. All mingled in together, dunno why they never sorted them.

When a project / job came up out would come the tin~ emptied onto a newspaper & sorted through until the right fixing for the job was found.

How many wasted hours sorting through all those different imperial fixings i wonder?

Well i;ve still got a 'tin' but it's childs play with metric.

Until you throw a few Metric fine nuts into the box and why not a few constant pitch ones as well so that M10 nut although the same thread form could easily have 4 different pitches.

For example I've used the usual metric coarse M6x1 for fixings on a model, the finer M6x0.75 where I wanted a finer thread and M6x0.5 on pipework due to the thin wall.

Jason beat me to it.

Isn’t the simple answer the drawings were created in the imperial age and being copyright they cannot be metricated. I assume most of the original designers are long gone, of not all. Modern day designers would I expect, at least in Europe and Australasia, create them in metric. Most Americans I think use imperial thought industry is shifting to the metric system. If you want to see more metric then create some new designs.

Absolutely, I said that about a hundred posts ago. Further more who would do the conversions, certainly not our suppliers. Boilers may be considered as new designs so could have to be reassessed etc. There is a considerable amount of inertia in the system.

regards Martin