An interesting co-incidence of units

[ZebethyalParticipant @zebethyal]

Michael,

I believe part of the problem here may be that the connection you refer to, whilst obvious to you seems to be less so to others, myself included.

I was reading your original post with interest, thinking there might me something new I could make use of, and whilst I agree that 1 1/4" is a relatively easy number to deal with and remember, I am really struggling to get my head around how 31.75mm or 31 3/4mm is useful, either as a standard, a multiple, or even to remember.

I was hoping you were going point out some easy number in both metric and imperial, like you did at the beginning 5" = 127mm, both being whole numbers and easy to remember.

Along with many others, I seem to have completely failed to grasp the concept in your original post, and would love a practical example where this co-incidence of units using 1 1/4" or 31.75mm can be used and show benefit over current methods of say multiplying by 25.4.

[Michael GilliganParticipant @michaelgilligan61133]

Zebethyal.

There may be no particulaly practical 'use' for this co-incidence [I use that word literally]; until one comes out of the blue. … That is why I chose the title for the thread !

I simply found it satisfying that one physical object could exactly represent several things on a 'human scale' : quarters of anything are easy to visualise; and a quarter of a millimetre is near the small-end of most people's visual range … likewise, five is an easy number; and 127 is towards the upper end of our visualisation limit.

As I have already said; it was just 'musings' presented in the vain hope that someone would be interested.

Sorry for wasting your time … I have already asked Jason to delete the thread, to avoid further embarrassment.

MichaelG.

[KWILParticipant @kwil]

How can a quarter of a millimeter be near the small end of most people's visual range?

A human hair is at least 10x smaller than that! If that is near, then I am glad "most people" are not involved in engineering,

[Mike PooleParticipant @mikepoole82104]

I do remember that 1 1/4" is 31.75mm as it is the standard bore for many grinding wheels and it struck me as a odd figure but when you realise it is a 1/4 of 5" it falls into place. I like the series of inch fractions that convert to fractions of a millimetre, there is something tidy about them, perhaps I have undiagnosed OCD. Irrational numbers do my head in.

Mike

[Michael GilliganParticipant @michaelgilligan61133]

Posted by KWIL on 30/01/2017 10:09:31:

How can a quarter of a millimeter be near the small end of most people's visual range?

A human hair is at least 10x smaller than that! If that is near, then I am glad "most people" are not involved in engineering,

.

I did not quantify 'near', but admit that I should probably have said "… near the small end of most people's comfortable visual range"

I have no further comment.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Mike Poole on 30/01/2017 10:39:21:

I like the series of inch fractions that convert to fractions of a millimetre, there is something tidy about them, perhaps I have undiagnosed OCD. Irrational numbers do my head in.

.

Thanks for that, Mike … I think it's the first positive response

MichaelG.

[MWParticipant @mw27036]

Am in the only one; as one of the metric generation, who uses ruler lengths as my point of reference to how long I want to imagine something is in imperial.

Like a 150mm ruler being 6" and 300mm being 12", which then is 1ft of course? It might not be totally accurate but it works for me.

I know i'll end up some way out if I added it all up but if I wanted to know the exact I could just calculate it. Like I said, I only use it as an imaginary guide.

 

Michael W

 

Edited By Michael-w on 30/01/2017 11:27:09

[duncan webster 1Participant @duncanwebster1]

Having read all of this thread the mandarins of the EU have decided to introduce the 'new inch', which will be 25.6mm. This will make things much easier as 1/16" will now be exactly 1.6mm, 1/4 will be exactly 6.4mm and so on, no messy 4 places of decimals to worry about. Unfortunately all your old imperial measuring tackle will now be out by 0.8%, but people who work in inches aren't that bothered about accuracy are they? This directive will take effect on 01/04/2017

[Michael GilliganParticipant @michaelgilligan61133]

déjà vu

[John HaineParticipant @johnhaine32865]

I'm at risk of being pedantic, but it seems that it may not be generally known that since the 1930s the "imperial" (and American) inch has been defined as precisely 25.4 mm. This was 1.7 millionths of an inch longer than the imperial standard.

[Gordon WParticipant @gordonw]

Isn't it amazing how people can get worked up over these things ? I'll say it again- things are the size they are, does not matter what units are used, so long as mating parts are in the same units. I'm off to the yard for fence timber and the like, 40mm is 1 1/2" , 100mm is 4". We all know it's not but the hens won't notice. Last time I was in France 1/2 kilo was called a pound, in french of course. Keep the 25.6 one for April 1st.

[Michael GilliganParticipant @michaelgilligan61133]

John,

If you were being pedantic, I think you would have used the word 'exactly' instead of the word 'precisely **LINK**

http://www.npl.co.uk/reference/faqs/on-what-basis-is-one-inch-exactly-equal-to-25.4-mm-has-the-imperial-inch-been-adjusted-to-give-this-exact-fit-and-if-so-when-(faq-length)

MichaelG.

[BazyleParticipant @bazyle]

Well I think this has been interesting as I will now remember 1 & 1/4 as thirty one and three/4 with the bold sort of repeat of '3' being a help. I will immediately approximate this to 32mm which is often seen as the bore of import lathes. So now I have a reminder of what that bore really is.

Also as a very popular lathe is a xx250 that's going to be its swing isn't it (?) at a nice round 10in if you grind off a bit of the ways and the big boys with a 280 have 280-250 = 32mm or 1 1/4 extra clearance.

[pgk pgkParticipant @pgkpgk17461]

Someone has to mention the following.

Zero inches and millimeters is the same distance as indeed is infinity in both metric and imperial and since there is both an infinite number of mm in an infinite distance and an infinitie number of inches in an infinite distance it follws than mm and inches are the same.

[John Stevenson 1Participant @johnstevenson1]

Is it cold outside today ??

[Neil WyattModerator @neilwyatt]

Hmm as Michael is continuing to post I can't see ianyt benefit in deleting this entertaining if somewhat peculiar thread.

If folks want a convenient integer conversion between metric and imperial 27432 millimetres is exactly 1 shackle or if that's too big for you there are exactly 1143mm in an ell.

Neil

<edit> easier to remember is 5,556 metres in a league.

Edited By Neil Wyatt on 30/01/2017 14:03:31

[John Stevenson 1Participant @johnstevenson1]

Just let me check my 0 – 1 Ell micrometer…………………………………………

[Martin KyteParticipant @martinkyte99762]

Depends how many infinities you think there are pgk pgk?

Martin

[IanTParticipant @iant]

The whole Imperial/Metric 'thing' is an oddly personal thing I find and I'm sure we all have our ways of moving between the two.

Being brought up on Imperial – I generally tend to visualise things that way. I "know" what an inch, a foot and a yard "look" like. I used to run the 100 yards and I still walk (and drive) in miles. But I also have a few simple conversions that I can do in my head. An inch is 25.4mm (so 2" is 50mm) and a metre is 39" (all near enough). I also know that there are 30 miles in 50 kilometres (again near enough). All easy – but thinking about this post – I realised I couldn't (immediately) say how many mm in a foot (it's 304.8 – but lets say 305!) and that I probably prefer to just remember that 10" is 254mm.

In my workshop practice, I'm still not exactly settled on either system. Most of my machines are old iron and have imperial dials, so I tend to machine (and think) in 'thous' but oddly when using CAD or measuring longer work/material lengths – I use mm. (am I alone in disliking cm?). It's partly because I've never been very 'fluent' in fractional measurements (although I know a guy who can add a list of fractional units at a glance). I do have a rule with 'decimal' inches on one scale but most of my rules just show either fractional inches or mm – and mm scales do seem easier to read.

I'm sure there are lots of folk reading this that just use one or the other system and it's not really a problem in practice… but for anyone 'new' out there who finds themselves in a 'mixed' metrology world there are two things that will really help. The first is knowing that 1mm = 40 thou (near enough) (or 4 thou = 0.1mm) and the second is having an A4 sheet handy in the workshop that lists the decimal 'inch' and 'mm' conversions of their fractional equivalents in 1/64th inch steps up to 1" (a simple spreadsheet will provide the data).

Anyway – if Michael wants to play with his numbers and find interesting 'intersections' then good luck to him.

Perhaps also – when I next need to convert 1.25" to mm, I might even remember that it's 31.75mm without having to reach for my calculator…

Regards,

IanT

[Neil WyattModerator @neilwyatt]

Give them an inch and they'll take 1.609 km.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 30/01/2017 14:01:15:

Hmm as Michael is continuing to post I can't see ianyt benefit in deleting this entertaining if somewhat peculiar thread.

.

Neil,

I only continued to post because no action had yet been taken to delete the thread, and in the meantime a couple of non-confrontational posts had been made; to which it seemed only poilte to respond.

On balance, however … I really wish I hadn't started it.

MichaelG.

[pgk pgkParticipant @pgkpgk17461]

Posted by Martin Kyte on 30/01/2017 14:20:02:

Depends how many infinities you think there are pgk pgk?

Martin

My Granddaughter used to count: One, two, three, lots..

As to specifically how many infinities then I suppose one starts by counting how many sets of parallel lines meet each other.

[DrDaveParticipant @drdave]

I will put my head above the parapet & say that I am with Michael on this one! Of the tools that I inherited from my Dad, probably the most prized one is a Rabone Chesterman 5 inch/127mm rule. It does not measure any better or worse than any other: it just has a "symmetry" that I find interesting.

[Michael GilliganParticipant @michaelgilligan61133]

Dr Dave … Thank You

Am I correct in thinking that's the No.33

Just found an ebay advert for a batch of New Old Stock

16 listed, and all 16 sold

MichaelG.

[DrDaveParticipant @drdave]

Posted by Michael Gilligan on 30/01/2017 20:49:32:

Am I correct in thinking that's the No.33

That be the one. And, no, you can't have mine!

[Author]

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