An interesting co-incidence of units

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John,

I'm quite sure that you already know [and I did say it was obvious!]

... five quarter inches is equal to 127 quarter millimetres

The only reason I mentioned it was that I thought [and still think] that a 1 1/14" reference piece is a convenient size, and 'meaningful' in both Imperial and Metric, and in both decimal and fractional series.

It appears that no-one else finds this interesting or potentially useful, so let's just let it die.

MichaelG.

On the other hand 10 quarter inches is equal to 254 10ths of a millimeter which is why most people use 1" = 25.4 = 25 4/10mm

I still don't see that 1 1/4 is that convenient in practical terms, the obivious one is that it is too large to set a nominam 1" mic or depth gauge. Most metric equipment is callibrated in 10ths and 100ths so teh 4/10ths works easier with that.

Maybe if you gave some actual examples of how teh 1 1/4" unit is convenient you could convince me?

J

Jason,

Frankly, I have no interest in trying to convince you.

For reasons that need not concern you, I needed some distraction yesterday and [for no good reason] ended-up musing over this ... I thought it interesting enough to share; but evidently It was not.

You have delberately made-light of the fractional connection, by only considering tenths.

My expectation was that since metric lathe slides are often calibrated in divisions of 0.025mm, thre might be some practical relevance.

I can't delete the thread, but you can : Please feel free.

MichaelG.

I always remember a metre as being 3ft 3 3/8" less 5 thou!

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.

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.

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 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

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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.

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

MichaelG.

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

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

déjà vu

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.

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.

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.

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.

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.

Is it cold outside today ??

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