Why is the world of model engineering still imperial?

[Chris Evans 6Participant @chrisevans6]

I spent my working life as a toolmaker. Probably half in imperial and half in metric based units as things changed over. I have no prefference until it comes to reading a depth micrometer. Instant with an imperial instrument but stop and look twice with a metric instrument. Nothing wrong with the measuring tool just my comfort zone.

Edited By Chris Evans 6 on 03/03/2023 20:03:08

[Martin KyteParticipant @martinkyte99762]

You can feel a thou with your finger.
You can still feel a thou when it’s 25.4 microns.

Beats me what all the fuss is about, it’s all just numbers.

[BazyleParticipant @bazyle]

Posted by JasonB on 03/03/2023 19:26:22:

Posted by UncouthJ on 03/03/2023 15:49:00:

Here's the debate ender… Fits n tolerances!………………………………………………

 

Is that why so many of those old imperial drawings don't mention fits and tolerances

No, it's because model engineering is not about mass producing interchangeable parts but making one off models where each part is made to fit its mate. Pre-metric modellers had enough common sense and ability to work out what they needed to know and just got on with it.

BTW in case people are not into music many great composers of previous centuries did not always write down every note of a now great orchestral work. They jotted down the main melody and key parts and the experienced orchestra were able to figure out the details.

 

Edited By Bazyle on 03/03/2023 20:45:00

[Another JohnSParticipant @anotherjohns]

Posted by JasonB on 03/03/2023 18:31:36:

You will also find that metric material is cheaper than a similar imperial size eg 25mm 230M07 is cheaper than 1" EN1A. Same with tools – how many imperial tools seem to be sold by the cheap far eastern suppliers and industrial suppliers over here don't keep much imperial these days

Jason! Oh to be living in such an enlightened country!

Over here (Canada) our main stocks of material come from the USA, so getting 25mm 230m07 or an equivalent steel, would have to shipped from Europe. Almost all materials are inch based. USA is 10x the population, and probably 50x the productivity, so…

[Chris MateParticipant @chrismate31303]

From a practical and cost savings and resuable part sizes perspective what is your opinion on imperial versus metric engineering uses. Does metric lead to parts looks similar but just not the same in measurements in comparaison to imperial. I always wondered about this.

[duncan webster 1Participant @duncanwebster1]

……. USA is 10x the population, and probably 50x the productivity, so…

Transatlantic arrogance creeping in? Population of USA 332 million, population of EU 447 million, UK 60 odd million, plus all the other countries in the world who use SI. As I've said before, this thread has become pointless, no country in the world is going to revert to imperial, it will die outside the USA when the last old crusty shuffles off this mortal coil, and good riddance (to imperial, not the crusty)

[samuel heywoodParticipant @samuelheywood23031]

I've no recollection of what we measured things in @ school, should have been metric i guess, but i've always done a rough in head conversion depending on what i was measuring. (now a more exact conversion with attempting to be a hobby machinist)

Flit from one to the other.

Big things~ feet.

Under one foot, i find cm convienient.

Little things~ well a thou or ten seems a lot more convienient than .0..whatever mm.

The Imperial system was,at least in part developed from the natural order of things?an inch~ width of your thumb, a foot~ well self explainatory as long as you have large feet , etc etc.

The Metre as i understand it, is the length it is because someone just decided it was so & bears no real relevance to anything real world. They just said a metre is 'this much' & we'll use that.

Metric system short changes you 4" x2" x 8ft Timber? you'll be lacking on all dimensions with metric.

Ever run the mile? Nowadays it's usually the 1500m.

All that said Duncan's probably right, the Imperial system will likely peter out eventually, when all the old & wise have departed this life.

Sometimes the' best' isn't the popular choice. Anyone remember VHS & Betamax?

Betamax was actually technically a better system, whilst being smaller, but Jo public went with VHS.

[Nicholas FarrParticipant @nicholasfarr14254]

Posted by samuel heywood on 04/03/2023 01:03:50:

I've no recollection of what we measured things in @ school, should have been metric i guess, but i've always done a rough in head conversion depending on what i was measuring. (now a more exact conversion with attempting to be a hobby machinist)

Snip

Sometimes the' best' isn't the popular choice. Anyone remember VHS & Betamax?

Betamax was actually technically a better system, whilst being smaller, but Jo public went with VHS.

 

 

 

Hi, not exactly, Betamax was the better system, but VHS won the battle because for whatever reason, more films were made commercially that the public could buy or hire, only a small fraction were for use on Betamax machines.

Regards Nick.

P.S. Betamax machines were more expensive at the time though.

Edited By Nicholas Farr on 04/03/2023 07:01:24

[JasonBModerator @jasonb]

Posted by Bazyle on 03/03/2023 20:44:04:

Posted by JasonB on 03/03/2023 19:26:22:

Is that why so many of those old imperial drawings don't mention fits and tolerances

No, it's because model engineering is not about mass producing interchangeable parts but making one off models where each part is made to fit its mate. Pre-metric modellers had enough common sense and ability to work out what they needed to know and just got on with it.

Agree with the way it's done in most home workshops, read any of my build threads and you will see me using one part to gauge the fit of another.

Many a pre metric modeller would seem to have an engineering background based what many members post here so would have been taught about fits etc. Now most coming into the hobby won't have gone through the apprentice system and may not even have done basic metalwork at school, they may have as much common sense but need to know how to apply it.

Funny enough I find the German and to a lesser extent the American drawings tend to give tolerances a lot more than UK ones which have very little and you may need an accompanying text to see if a part should be bare of full but I've yet to find a mic that reads in those amounts be it a metric full or an imperial full but the old boys would have known by the feel of their firm leg callipers as an even older boy would have taught them..

[Martin ConnellyParticipant @martinconnelly55370]

Surely the claim that understanding the values 0 to 5 thou is better than the metric equivalent is simply personal preference. As someone who had to work in both units for most of my working life I know that 1mm is about 40 thou (39.37, close enough for estimating which is what people are suggesting here) so 4 thou is about 0.1mm 1 thou is about 0.025mm. I can add 0.1 and 0.025 and combinations of these to get 1, 2, 3, 4, 5 thou, and vice versa, without having to resort to paper and pencil or calculator.

Martin C

[JAParticipant @ja]

I strongly believe fits and tolerences have a place in model engineering but I am at a loss to understand their relevance to the Imperial -v- Metric arguement.

Perhaps they are being used just to spice up this ancient, pre-deluvian, arguement.

JA

[Martin KyteParticipant @martinkyte99762]

Perhaps not quite back to the flood but certainly the French Revolution and Napoleon.

:0)

Martin

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Martin Kyte on 03/03/2023 20:43:37:

You can feel a thou with your finger.
You can still feel a thou when it’s 25.4 microns.

Beats me what all the fuss is about, it’s all just numbers.

.

+1

… or +25.4 for that matter

MichaelG.

.

Edit: __ of course, the ‘missed opportunity’ was when they failed to make the ‘exact’ conversion 1: 25.6

Edited By Michael Gilligan on 04/03/2023 10:15:13

[Graham TitmanParticipant @grahamtitman81812]

I cannot understand why this keeps coming up if you do not like imperial convert it to metric no problem easy. Where i worked in the seventies the companey took all the grants and converted the drawing office to metric one small problem EVERY machine was imperial cheap way out every machine had a calculater and no winging for weeks after we just sat there for a few minutes and played with  25.4 to three decimal places and got on with it.Jobs were done

Edited By Graham Titman on 04/03/2023 10:12:46

[John AbsonParticipant @johnabson65530]

I've noticed an increasing move in ME to use metric dimensions. It makes procurement of standard materials and tools easier and in some cases cheaper, in the UK at least. DROs especially on milling machines – 'once you've used one, you'll never go back' seems common – simply switch between metric and inch. Even my digital calipers do the same.

Fits and tolerances really don't come into it, once you've made the mental adjustment (OK, some people will never make that jump, but that's not because of the measuring system base IMO).

I spend a lot of my life restoring and making parts for old pipe organs, all made to inch dimensions. Makes a lot more sense to use inch on those, but metric on more recently built instruments. Errors are less and its easier to measure in the respective measuring system base used on the original. Likewise, when building a model designed in inches, one is better sticking to inches.

I was recently 'given' a Bosch tape measure as a promotional giveaway. Functionally it's the best tape measure I've ever owned (and I've lost dozens and found a few ) but is only marked in metric. After about half a day, I felt liberated from the tyranny of the inch!

/J

Edited By John Abson on 04/03/2023 10:24:39

[JasonBModerator @jasonb]

As I said before simply doing the mathmatical calculation is not really a proper conversion to metric that 12.7 x 0.623pitch tap will be hard to find so you are only changing numbers not physical parts and associated tooling.

I suppose most people put up with it and those that do change a set of drawings to a full metric conversion just tend to keep them to themselves rather than make them available to others. Probably not helped by the Likes of Stuart's who are often suggested as the source for "your first casting set" who supply the materials and fixings too. Most buying a kit will tend to buy BA and make use of the supplied material and now on the slippery slope will slide into the imperial/BA way it has always been done. If they just supplied castings then I bet there would be a lot more metric 10Vs about as the drawings are out there.

[SillyOldDufferModerator @sillyoldduffer]

Posted by UncouthJ on 03/03/2023 19:40:55:

Posted by Nicholas Wheeler 1 on 03/03/2023 18:32:39:

Posted by UncouthJ on 03/03/2023 15:49:00:

Here's the debate ender… Fits n tolerances!

You can pretty perfectly gauge an amount of slop in a slip, or an amount of welly on an interference in a handful of thou. Tell me you can do that so simply in metric so I can call you a liar 😉

Do you really think that metric engineers/machinists/fabricators/etc can't do that, or judge by eye to similar precision?

Yes actually. Don't care what language you speak, the 0-5 thou difference either way is infinitely easier to account for without looking anything up. Remember the focus of this forum is the hobby engineer, not the daily jobber.

I know that up to a couple thou interference, I'm probably ok with the mallet, any more than that and I'm going to the press, no charts required. You can only do that in metric if you already know the values, which are a lot less simple than 1 or 2…

J

J reveals a misunderstanding of fits and tolerances I fear!

'You can pretty perfectly gauge an amount of slop in a slip, or an amount of welly on an interference in a handful of thou.' isn't working to a tolerance, it's "Fitting" in the old fashioned sense. This is not working to a tolerance, because that requires dimensions to be measured carefully. Measurements must done with a micrometer, with go-no gauges, jigs and fixtures, or calibrated machines, never 'judged by eye'.

Old-fashioned fitting is how I work. The system uses the work itself as a series of gauges, each part being trimmed to fit into another. Accurate measurement isn't required, and stuff can be judged by feel. Fitting works in any system of measure, Uncouth can believe I'm lying if he wants, but I do the same as he does in metric.

Fitting is great for home-workshops and repair work, but it fails miserably for production work. First problem, is that fitting is hideously expensive because the work is both skilled and labour intensive. Chaps who do it burble on about 'quality', but never mention productivity, which is rock-bottom. Worse, fitted components aren't interchangeable. If the parts from 20 PottyMill engines were scrambled and re-assembled, it's unlikely that any of the engines would work, and those that do are luck rather than engineering.

Interchangeability is achieved by setting tolerances and knowing for certain that all the parts are accurately machined to fit together by design. Parts made at different times and places can be brought together and assembled without 'judging slop with a slip'. If that's necessary, something has gone horribly wrong.

Fortunately interchangeability is rarely important in home-workshops. It's why I don't own any slip gauges, or anything better than a 0.01mm micrometer. I've even experimented with making stuff using plain calipers as comparators only. Works surprisingly well with care. The method knows nothing of 'thou': it's all done by feel.

Perhaps the worst feature of Imperial is it seems cuddly friendly at first. But first contact is misleading. It's rather like discovering the house of your dreams is built over a 200 fathom deep mineshaft full of chemical waste. All you have to do is ignore a few cracks in the walls and an occasional hint of Phosgene in the kitchen.

My point is purchasers might do better to buy an equally good house that doesn't have faulty foundations. Even if you personally don't understand a survey full of weird technical terms!

Always good to tilt a debate on it's head. As Duncan says, none of the world's metric users sees any advantage in Imperial. The only reason it's used is to supply legacy markets, almost never for new design. Imperial is gradually fading, even in the US.

Like it or not, Imperial measure is obsolescent. It's damaging to to foist it on the next generation. Don't stuff up the kids with Imperial, or any other old friends, when something better is available or time has marched on.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Abson on 04/03/2023 10:23:35:

[…]

After about half a day, […]

.

0.5 day in Metric

MichaelG..

[Dave HalfordParticipant @davehalford22513]

Posted by samuel heywood on 04/03/2023 01:03:50:

I've no recollection of what we measured things in @ school, should have been metric i guess, but i've always done a rough in head conversion depending on what i was measuring. (now a more exact conversion with attempting to be a hobby machinist)

Flit from one to the other.

Big things~ feet.

Under one foot, i find cm convienient.

Little things~ well a thou or ten seems a lot more convienient than .0..whatever mm.

The Imperial system was,at least in part developed from the natural order of things?an inch~ width of your thumb, a foot~ well self explainatory as long as you have large feet , etc etc.

The Metre as i understand it, is the length it is because someone just decided it was so & bears no real relevance to anything real world. They just said a metre is 'this much' & we'll use that.

Metric system short changes you 4" x2" x 8ft Timber? you'll be lacking on all dimensions with metric.

Ever run the mile? Nowadays it's usually the 1500m.

All that said Duncan's probably right, the Imperial system will likely peter out eventually, when all the old & wise have departed this life.

Sometimes the' best' isn't the popular choice. Anyone remember VHS & Betamax?

Betamax was actually technically a better system, whilst being smaller, but Jo public went with VHS.

 

B&Q still sell 8×4 sheets of ply etc disguised as metric 2.44M x 1.22M so they have gone metric sort of.

 

PS Video 2000 was the best system with auto tracking.

Edited By Dave Halford on 04/03/2023 10:52:42

[John AbsonParticipant @johnabson65530]

Posted by Michael Gilligan on 04/03/2023 10:50:57:

Posted by John Abson on 04/03/2023 10:23:35:

[…]

After about half a day, […]

.

0.5 day in Metric

MichaelG..

Nice one!

However there are 24 hours in a day so time is definitely Imperial based (yay!!) John Harrison was, after all an Englishman – oh crikey, are degrees of latitude and longitude metric or imperial??? (think I'll just go and hide!)

[Dave HalfordParticipant @davehalford22513]

There's also the world of telecom's equipment.

American 19" wide racks use a height unit of an U which is 1.75" or 44.5mm by 482mm wide

European ETSI 21" wide racks use a height unit of an SU which is 25mm or 1" ish by 533mm wide.

So what should be Metric isn't always.

[Martin KyteParticipant @martinkyte99762]

Posted by John Abson on 04/03/2023 10:58:30:

Posted by Michael Gilligan on 04/03/2023 10:50:57:

Posted by John Abson on 04/03/2023 10:23:35:

[…]

After about half a day, […]

.

0.5 day in Metric

MichaelG..

Nice one!

However there are 24 hours in a day so time is definitely Imperial based (yay!!) John Harrison was, after all an Englishman – oh crikey, are degrees of latitude and longitude metric or imperial??? (think I'll just go and hide!)

Babylonian actually.

Regards Martin

[Clive SteerParticipant @clivesteer55943]

I'm rather late to this subject but it is not only model engineering that is Imperial as electronic components are often on Imperial 0.1 inch pitch. I'm happy to work in either measurement system but the whole concept of fractions makes arithmetic excruciatingly difficult and rather like doing sums using Roman numerals and a recipe for error.

CS

[duncan webster 1Participant @duncanwebster1]

Just to be pedantic (who me?) I think 24 hour day was from ancient Sumeria via ancient Egypt, it is 60 minutes in an hour that is Babylonian. Bit difficult to claim this as imperial, and it's fairly widespread in the rest of the world. Use of 12 is also Sumeria, it comes from 4 fingers each having 3 knuckles, then you have 12 hour day and 12 hour night.

As regards tolerances, when Ford were asked to consider making Merlins, they stated they couldn't work to RR, tolerances. Not because they were too tight, RR used selective assembly and fitting when building engines, for mass production you need much tighter tolerances so thar you just pick up parts and assemble them, no faffing about.

[Mike PooleParticipant @mikepoole82104]

Our time and motion men used stop watches that used centiseconds, it made it much easier to add the individual parts of a process together to get an answer in seconds.

Mike

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