Old rule divisions twelfs etc

[CirclipParticipant @circlip]

What fractional notation applies to 7490/18773 ?

Regards Ian.

[Michael GilliganParticipant @michaelgilligan61133]

Unsurprisingly, Dave …

A scale divided into 127ths of an inch would be interchangeable with one having 0.2mm divisions

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Circlip on 30/09/2021 11:11:55:

What fractional notation applies to 7490/18773 ?

Regards Ian.

.

7490/18773 … as you presumably well-know

What was the point of your question ?

MichaelG.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Dave, I think you'll find that 45/64" is about as close as one might get with a rule if that is all that is available, 45/63.5 being equal to 90/127

Regards Nick.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 30/09/2021 10:41:05:

.

And this is what the inch fraction ¹⁄₁₂₇ scale looks like, magnified!

If the pictured scale looks uneven on your screen, its because ¹⁄₁₂₇" pushes display technology – jpeg photos and the your computer screen both struggle,

[…]

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Having tapped on your picture of the scale, to expand it … then done a screenshot … then converted that .png back to .jpg for the forum … I think my iPad handles that pretty well : I can even see the dots on your Grid.

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Click for a larger view ^^^

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Certainly good enough to see the nominal resolution of the scale, even if not to assess its accuracy/linearity.

MichaelG.

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P.S. __ ‘sub-graduations’ could be added according to taste … there is no need for them to be integer divisions of 127 … they are simply an aid to counting.

Edited By Michael Gilligan on 30/09/2021 13:38:21

[Nick WheelerParticipant @nickwheeler]

Michael, your 'clear' image is about 5" across on this device, and is therefore utterly useless as a defence of a scale that doesn't work in real life.

And Imperial measurements have enough stupid divisions without some idiot enthusing about 1/127s !

[Brian GParticipant @briang]

I must confess that however useful a rule calibrated in 127ths might be, I cannot easily make out anything much smaller than the 1/127" markings on my rule, needing a magnifier to read the 1/254" scale. There is evidently a market for unusual imperial rules as Starrett's "no.1" graduation for rules includes not only the usual 16ths, 32nds and 64ths but also 12ths, 24ths and 48ths as well as 10ths, 20ths, 50ths and 100ths (handy for thou dimensions) and even 14ths and 28ths. I can sort of see the point of 12ths for scale drawing but 14ths! Drawing year planners perhaps?

Brian G

[John ReeseParticipant @johnreese12848]

Posted by Nicholas Wheeler 1 on 30/09/2021 18:55:40:

Michael, your 'clear' image is about 5" across on this device, and is therefore utterly useless as a defence of a scale that doesn't work in real life.

And Imperial measurements have enough stupid divisions without some idiot enthusing about 1/127s !

I have seen scales in 1/128" graduations and at least one twist drill sized in 1/128ths. I have a wooden rule graduated in whole inches only.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Nicholas Wheeler 1 on 30/09/2021 18:55:40:

Michael, your 'clear' image is about 5" across on this device, and is therefore utterly useless as a defence of a scale that doesn't work in real life.

 

And Imperial measurements have enough stupid divisions without some idiot enthusing about 1/127s !

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I will accept your written apology for that personal insult when you care to post it.

… You have evidently mis-understood the preceding discussion.

MichaelG.

Edited By Michael Gilligan on 30/09/2021 21:34:42

[Nigel Graham 2Participant @nigelgraham2]

I am not quite clear where that 1/127 came in but I did have a steel rule that had one inch divided into 1/128.

Quite how the manufacturers thought anyone could read that, is anyone's guess!

More useful though not in the workshop, was an acrylic rule with one of those diagonal scales that allow measuring tiddly bits of inches without needing a microscope. I think I still have it, but have forgotten how they work, beyond using a similar-triangles principle, though was taught it at school.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Nigel Graham 2 on 30/09/2021 23:31:54:
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I am not quite clear where that 1/127 came in but […]

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Dave asked for the ‘fractional inch’ equivalent of 18.0mm

… which is 90/127

MichaelG.

[david bennett 8Participant @davidbennett8]

These exotic fractional inches may be accurate and precise, but of no practical use to model engineers until they are "translated" into practical measurements such as mm. How would you turn a piece to 90/27"  diameter and how would you measure it?

 

Edited By david bennett 8 on 01/10/2021 02:34:25

Edited By david bennett 8 on 01/10/2021 02:38:08

Edited By david bennett 8 on 01/10/2021 02:50:16

Edited By david bennett 8 on 01/10/2021 02:50:41

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 30/09/2021 11:32:50:

Unsurprisingly, Dave …

A scale divided into 127ths of an inch would be interchangeable with one having 0.2mm divisions

MichaelG.

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David … Did you miss this ^^^ post that I made yesterday ?

… if so, I commend it to your attention.

MichaelG.

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P.S. __ I am assuming that your 90/27 should read 90/127 … that was the fraction under discussion.

[Michael GilliganParticipant @michaelgilligan61133]

[ once more … with feeling ]

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.

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 01/10/2021 08:07:52:

[ once more … with feeling ]

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.

MichaelG.

Still with you Michael! My response is a rule graduated in 0.2mm increments isn't much practical use either – not without a microscope.

This table shows what I don't like about fraction rules. It spans one inch assuming the user has rules graduated in eighths, tenths, twelfths, twentieths, and sixty-fourths.

The table can be eyeballed to see 3/8" is smaller than 25/64" which is smaller than 2/5, which is smaller than 13/32". They all approximate 10mm and 25/64" is the closest. But, as a general way of measuring, it's fairly obvious from the decimal fractions that the usual common fractions don't step evenly: they jump.

The graph has a sawtooth rather than a straight line:

In practice, this means it's best to work with a limited range of common fractions when using rules. Although you could have several rules, making anything dimensionally complicated is clumsy compared with working throughout in decimal fraction such as thou. Thou and millimetres are smooth, for example it's easy to go to tenths or nanometres when more accuracy is needed. But not measured with a rule!

Michael: I suspect some of our exchanges are being misunderstood: we're perhaps being a tad pedantic or arcane for most tastes. For the avoidance of doubt, Michael and I aren't having an argument! And I don't think I'm doing a good job explaining myself, so apologies for not being clear. Maths isn't my best subject.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 01/10/2021 11:01:53:

Still with you Michael! My response is a rule graduated in 0.2mm increments isn't much practical use either – not without a microscope.

[…]

Michael: I suspect some of our exchanges are being misunderstood: we're perhaps being a tad pedantic or arcane for most tastes. For the avoidance of doubt, Michael and I aren't having an argument! And I don't think I'm doing a good job explaining myself, so apologies for not being clear. Maths isn't my best subject.

Dave

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Thanks for that comment, Dave

… I was going to describe our exchange as sparring

There is no winner or loser, we are just exercising our minds to mutual benefit.

MichaelG.

Edited By Michael Gilligan on 01/10/2021 11:18:40

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 01/10/2021 11:01:53:

Still with you Michael! My response is a rule graduated in 0.2mm increments isn't much practical use either – not without a microscope.

[…]

.

Accepted, Dave

But, I’m never far away from a microscope

One of my oft-used scales is only 1mm long … divided into 100 divisions of ten microns.

So I don’t really perceive the need for magnification as a practical disadvantage.

MichaelG.

Edited By Michael Gilligan on 01/10/2021 11:27:28

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Dave (SOD), I don't class myself as a mathematician, but I do like playing around with numbers even if they make no practical sense or even have any useful purpose**. Some fractions do have a usefulness in some instances though. I like the fact that 1/127 is equal to 0.02mm which can make some ridiculous improper fractions, some of which one can measure quite accurately with a rule for general use, with either metric or imperial. e.g. 7500 / 127. The 1/127 also has a *1/2- brother, which will follow it continuously e.g. 15 / 254 They are of course a bit quirky and maybe many will not spot these fraction measurements in mm.

**Does make the old grey cells work a little though.

* Thought I'd use a fraction here on purpose.

Regards Nick.

[old martParticipant @oldmart]

I have two 12",300mm chrome face stainless steel Rabone/ Rabone Chesterman rules that have millimeters and half millimeters on one side, and 1/16, 1/32 and 1/64 of an inch plus 1/10, 1/20, 1/50 and 1/100 of an inch. I find the 1/100" rather difficult to see and use, and the half millimeters difficult also. With the metric side, I prefer to use the millimeters and judge the parts of by eye.

[david bennett 8Participant @davidbennett8]

Posted by Michael Gilligan on 01/10/2021 07:53:11:

Posted by Michael Gilligan on 30/09/2021 11:32:50:

Unsurprisingly, Dave …

A scale divided into 127ths of an inch would be interchangeable with one having 0.2mm divisions

MichaelG.

.

David … Did you miss this ^^^ post that I made yesterday ?

… if so, I commend it to your attention.

MichaelG.

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P.S. __ I am assuming that your 90/27 should read 90/127 … that was the fraction under discussion.

No, I did not miss that post, but that was not what I asked. How woul I turn a piece to 18mm diam. within 0.03mm ?

This is about precision. Numbers are precise by definition Rules are not.

Dave8

[Michael GilliganParticipant @michaelgilligan61133]

Posted by david bennett 8 on 01/10/2021 20:23:02:

[…]

No, I did not miss that post, but that was not what I asked. How woul I turn a piece to 18mm diam. within 0.03mm ?

This is about precision. Numbers are precise by definition Rules are not.

Dave8

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Well … I don’t think that’s not actually what you asked

[quote]

Posted by david bennett 8 on 01/10/2021 02:31:30:

These exotic fractional inches may be accurate and precise, but of no practical use to model engineers until they are "translated" into practical measurements such as mm. How would you turn a piece to 90/27" diameter and how would you measure it?

 

Edited By david bennett 8 on 01/10/2021 02:34:25

Edited By david bennett 8 on 01/10/2021 02:38:08

Edited By david bennett 8 on 01/10/2021 02:50:16

Edited By david bennett 8 on 01/10/2021 02:50:41

[/quote]

.

But anyway,David : I’m not really interested in being ‘tested’ on this … Dave and I were having an interesting discussion until Nicholas Wheeler was so rude, and then you joined in with your ‘challenge’

It’s not actually difficult, and nor is it particularly important. … If you ever need to do it, I’m sure you can find a way.

MichaelG.

Edited By Michael Gilligan on 01/10/2021 20:48:48

[david bennett 8Participant @davidbennett8]

Pease do not ink me with Nicholas Wheeters comments. I had no intention of joining in, or being rude.

Dave8

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for that, David … I appreciate it.

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Measuring, and working to, 0.03 mm should be relatively easy.

0.03 / 25.4 = 0.001081024" or 2.3622047 * 10^4, 1/127s, according to my calculator.

0.0254 mm is ABOUT 0.001". I believe

Am not going to claim that those figures are accurate or precise.

Howard

[JasonBModerator @jasonb]

Howard is that working with a rule or a micrometer?

[Author]

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