Learning to Love the Metrinch

[Geoff TheasbyParticipant @geofftheasby]

No-one seems to have mentioned Patternmakers' rules.

Geoff

[KWILParticipant @kwil]

Patternmaker's rules not mentioned? That is because they do have a use unlike the EU.

[Neil WyattModerator @neilwyatt]

OK, I know some of you aren't taking this seriously, and I can see why, but I have found some more details and it starts to make sense.

It;'s all about rationalising the supply of non-precision sized materials in fractional sizes. So 1" PGMS or Silver steel will still be 1.000" and 25.4mm (within whatever tolerance you want to pay for)

The tolerance bands will be shifted for fractional sizes of things like BDMS, aluminium extrusions and so on (ref. the recent discussion on how big the tolerance bands are fro drawn alloy tubes). In these cases the 'metrinch' will be used (i.e. 25.6mm rather than 25.4mm) and the 'official size' of fractional stock will be 1.0078% larger.

This means all fractional stock down to 1/256 of an inch (in practice little is produced below 1/32" steps) will translate to exact sizes to 0.1 of a mm. These sizes are already within existing tolerance bands for nearly all products affected. For example a 3/8" bar will 'officially' be exactly 9.60mm rather than 9.525.

This will greatly simplify the design process for any projects using mixed imperial and metric stock (i.e. you can specify standard metric size tooling (available in 0.1mm steps) for any task using non-precision imperial stock.

The rumour is that this is actually Brussels running up the white flag and accepting that the imperial system is here to stay and that, in some parts of industry (those dealing with the USA, at least) some aspects of metrication may be rolled back.

In practice, it will have little more impact than the fact that number drills are now actually made to metric, not imperial, dimensions.

Neil

[Another JohnSParticipant @anotherjohns]

Neil; I know that it's April 1st and all that,

Being north of the border, (the USA one) I understand the focus on inches. But, looking at the 3D printer group in the USA, they all seem to speak (and, comprehend) metric.

I think metric is better understood in the USA than we might at first think; maybe in 10 or 20 years, metric will indeed be a unifying force for manufacturing around the world.

John.

[JasonBModerator @jasonb]

Neil, I was sent this flyer by one of my suppliers today, maybe it would be the ideal place for you to sit and google the metrinch some more

 

I had heard that the US were going to use a similar system but just to be different to the rest of the world they will adopt the "imperimetre"

Edited By JasonB on 01/04/2015 12:52:27

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 01/04/2015 11:09:36:

It;'s all about rationalising the supply of non-precision sized materials in fractional sizes. …

For example a 3/8" bar will 'officially' be exactly 9.60mm rather than 9.525. …

In practice, it will have little more impact than the fact that number drills are now actually made to metric, not imperial, dimensions.

.

… Thus making them the wrong size

[Neil WyattModerator @neilwyatt]

Well I hope there aren't too many deeply upset folks.

I've had a regular trickle of emails and a few phone calls from concerned readers! I started this thread early because it was mentioned in the magazine and I wanted somewhere to 'send' folks who wanted to know more.

Even my daughter rang me up to say she hopes I don't get beaten up my enraged readers who have thrown away their out-of date tools.

I could have written a book on this – how it would have prevented the Hubble mirror cock-up and saved Mars express, and how the success of Rosetta and Philae in reaching a comet was partly down to an early trial of using the system. Then there was the NATO angle (the various types of 'mil&#39.

Of course the irony is that back in the 70s Model Engineer was carrying editorials and articles warning us that imperial equipment and stock was soon to disappear…

Neil

[mark costello 1Participant @markcostello1]

I reside across the pond and Metric is not better understood than is widely believed. Our inch is not broken and no need to fix it.

[Neil WyattModerator @neilwyatt]

I totally agree Mark, as Lambton pointed out earlier, your inch was 'fixed' in July 1959

Neil

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