Converting fractions to decimals

[Ramon WilsonParticipant @ramonwilson3]

Not seen a calculator like that before Michael – as a matter of interest how do you actually put in the 1 and 11/16

(11 divided by 16 + 1 is usually good enough for me)

I had to re read that last post twice BTW

Ramon (Tug)

[Michael GilliganParticipant @michaelgilligan61133]

Here is help screen :

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MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Ramon Wilson on 17/08/2021 08:32:51:

 

 

(11 divided by 16 + 1 is usually good enough for me)

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But the calculator will also handle sequential addition, etc. of fractions.

It also displays its ‘work’ on another page if you click the ‘button’ at top right

MichaelG.

 

Edited By Michael Gilligan on 17/08/2021 08:54:08

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I can get the same answer on two of my calculators, however the answer is displayed as an improper fraction and will have to be recalculated to obtain the answer in true mm.

Which works out to 42.8625.

Regards Nick.

P.S. I wouldn't have thought to calculate in this manner if MichaelG hadn't posted about the one he has shown.

Edited By Nicholas Farr on 17/08/2021 10:09:41

[Roderick JenkinsParticipant @roderickjenkins93242]

For workshop use I like to use a calculator like this **LINK**

You can select the number of decimal places displayed and round the last figure. Normally I am calculating mm to thous so I divide by 25.4 and the answer is displayed to three decimal places – the nearest thou.

Rod

[egaParticipant @ega]

Has anyone mentioned the "Digital Caliper with Fractions"? I find my Wixey brand version quite useful for converting between fractions/decimals/millimetres.

The fraction/decimal equivalents are not precise, however; eg "0.061 to 0.065" is shown as 1/16".

[JasonBModerator @jasonb]

As I mentioned yesterday I now like to redraw a design as it's a good way to check things or alter for say metric fixings. Alibre lets me enter say the diameter of a circle in imperial fractions

Then when I OK that either with a mouse click or return key it will size the circle and display it in the format set for the drawing in this case 3 decimal place metric

But would just as easily show it in imperial if I set teh drawing properties to that.

When I come to do the 2D drawing then I can have it in whichever form I set be that Imp fractions, imp decimal, metric or even dual dimensions.

Edited By JasonB on 17/08/2021 10:26:58

[Ramon WilsonParticipant @ramonwilson3]

Thanks Michael –

The calculator that I would like on my bench I don't believe is available – well I've never seen one despite a good search at times

Along with just the basic functions it would only feature the trig functions and basic 'scientific' features but with a direct conversion to and from metric.

Big read out and and big keys like Rod has just shown would be a bonus too

If anyone knows of such I'd like to hear of it.

I recently bought another (Tesco) scientific calc to replace my old and abused (visually) one – it works in a completely and unintelligble (to my old brain) manner from all previous scientific ones used so sits here pristine but redundant – free to anyone who would like it

As I slide toward the end of the perch however I have little desire to replace something, neither physically or mentally which has served me well for far too long to remember which will take time away from what active modelling time I have left – others may see different but that's me I'm afraid

Regards – Tug

[JasonBModerator @jasonb]

The other option which is likely to fit what was said in the opening post of converting drawings to what a "modern young engineer might get to grips with" is to forget giving him a pile of paper and present him with some CAD files so that he can then work with those either printing out on paper, send off DXF files for laser/water cutting, 3D printing parts or jigs or just take the part file and process it in his CAM package so the CNC can spit it out.

CAD can make this easier, as you will know most castings are only dimensioned on the parts that need to be machined so no calculator or other conversion will work without a known figure to input. Easy in CAD as you can use the "Trace" function to import a scan of the original drawing, etching or photo depending on what you are working from. Then make adjustments for any distortion and scale it if you want to reproduce the model in another size and then simply use the image to position the construction lines to draw the actual casting.

Here for example is the main bracket from my Heinrici engine scanned, scaled etc and I have started to add the two bearing bosses as they are at known positions.

It's then just a case of adding the rest or the lines and thicknesses etc to get your "casting"

I did not even bother printing it out on paper, just into the CAM and then onto a USB stick to go into the CNC. I could also have used CAD to add draft angles, machining allowance and shrinkage allowance so a pattern could be made for traditional casting.

This is how a modern young engineer is likely to do it. I'm not saying I'm that young but I do use some of the modern methods. Though I don't have the equipment to 3D scan in an old unobtainable casting and 3D print a new pattern or just print it straight out in metal.

[CirclipParticipant @circlip]

Plenty of room on my Luddite Bench Ramon, I too know there's 25.4mm to the inch and don't find it too difficult to convert fractions. An ex technical director used to tear his hair out when I used LOG tables (Skool edition) to work out angles of bend and blend lengths on Loco exhaust systems despite his Tecky calk. Batteries NEVER run out on log tables. But just think, if you invested in a "Tormack" how much more sailing time you could enjoy by pressing a few buttons and letting the power of electrons generate some of your exotic engines?

Regards Ian.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Ramon, can't help you for your ideal calculator, but as far as big readout and big keys, I got this one from Tesco's many years ago. It only has basic functions but does include square root, at the moment though, it only works with a light or in good daylight with the solar panel, as one of the battery wires has broken of one of the terminals and it will need opening up to fix it. Don't use it much, but I did tease my eldest granddaughter once by saying you need a big calculator to work out sums with big numbers and I showed her this one.

Regards Nick.

Edited By Nicholas Farr on 17/08/2021 11:14:50

[John HaineParticipant @johnhaine32865]

I'm bemused by all this. I haven't used fractions really since I did basic arithmetic, whether I'm using inch or metric measurement. If I need to convert I do it in my head or use the calculator on my phone. This has a basic one provided but I usually use a freeware app called Free42 that emulates an HP42.

[SillyOldDufferModerator @sillyoldduffer]

Posted by ega on 17/08/2021 10:01:10:

Has anyone mentioned the "Digital Caliper with Fractions"? I find my Wixey brand version quite useful for converting between fractions/decimals/millimetres.

The fraction/decimal equivalents are not precise, however; eg "0.061 to 0.065" is shown as 1/16".

The 'not precise' shortcoming is an important point well worth emphasising! My Digital Caliper with Fractions is pretty untrustworthy in fraction mode, just as ega's Wixey demonstrates with ¹⁄₁₆" actually being ±0.002". In fraction mode, my caliper's reported ¹⁄₁₆" could be 4 thou out, which is a lot! In comparison, the same instruments decimal error is about 1 thou.

All fraction calculators suffer to some degree from this inaccuracy, though the more sophisticated versions do far better than simple minded digital calipers. Michael's example is close: his calculator (and Nick's) both give 1¹¹⁄₁₆ x 25.4 = ³⁴²⁹⁄₈₀. So does mine. However, the real answer is ⁹⁶⁵¹⁷⁷⁶⁹⁵¹⁴⁰⁸³⁹³⁷⁄₂₂₅₁₇₉₉₈₁₃₆₈₅₂₄₈. Don't panic, ³⁴²⁹⁄₈₀ is an excellent result, the error being only -²⁷⁄₁₁₂₅₈₉₉₉₀₆₈₄₂₆₂₄₀.

Highlights a serious problem with fractions because the level of inaccuracy of each calculation depends on the individual ratio and on the number of display digits available. Thus it's hard to tell when fraction calculators are:

• exactly right as in 12 x ¾ = 9
• nearly right, as in 1¹¹⁄₁₆ x 25.4 = ³⁴²⁹⁄₈₀
• seriously misleading as in ¹⁄₁₆" being anywhere in the range 0.061 to 0.065"

Decimals are undoubtedly safer in engineering because the number of digits is a strong clue to the underlying accuracy. Safer rather than perfect, beware the dingbat claiming pi=3.1428571428571427937!

Dave

[Ramon WilsonParticipant @ramonwilson3]

Well you are probably right Jason with regard to a 'modern young engineer might get to grips with it' but the operative word is might and of course a newcomer to the hobby may not be so young after all.

I spent my working life machining conventionally until the last couple of years or so DRO being the only 'modern' aid until the Haas CNC machining centre came along. Ten or more years too late for myself from a working point of view and fascinating to learn and satisfying to see what you had programmed in use but it's not and never was even considered as something I wanted to bring into my home workshop.

I think I said before – I count myself as a dino-sore but the things learnt and used over the years are still relevant and, importantly, still allow me to come up with the goods

Sometime back on another Forum I was told these three engines could not be built without, and I quote, "bringing myself into the modern world and learning 3D CAD" – I was simply "twenty years too late". Well I didn't and I haven't but as always proof is pudding shaped

No computer aided anything was injured or harmed in the construction of these Tigers

Nice to think I'm not in luddite isolation Ian – I'm afraid its all I'm likely to be from here on.

Nicholas – that's the kind of thing I'd like but with those other functions – as the brain is fading so are the eyes I'm sad to say

Carefull now John (Haine) Converting fractions in your head ??? the mind boggles – well, 1/4 might be .250 even 6.35mm but that's memory – 27/64 or similar is most definitely another matter.

Great to chat guys

Regards – Tug

[Michael GilliganParticipant @michaelgilligan61133]

Posted by SillyOldDuffer on 17/08/2021 12:03:49:

[…]

All fraction calculators suffer to some degree from this inaccuracy, though the more sophisticated versions do far better than simple minded digital calipers. Michael's example is close: his calculator (and Nick's) both give 1¹¹⁄₁₆ x 25.4 = ³⁴²⁹⁄₈₀. So does mine. However, the real answer is ⁹⁶⁵¹⁷⁷⁶⁹⁵¹⁴⁰⁸³⁹³⁷⁄₂₂₅₁₇₉₉₈₁₃₆₈₅₂₄₈. Don't panic, ³⁴²⁹⁄₈₀ is an excellent result, the error being only -²⁷⁄₁₁₂₅₈₉₉₉₀₆₈₄₂₆₂₄₀.

Highlights a serious problem with fractions because the level of inaccuracy of each calculation depends on the individual ratio and on the number of display digits available. […]

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You must try harder, Dave

Here is the calculation, in fractions:

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The fractional answer is correct

MichaelG.

[duncan webster 1Participant @duncanwebster1]

But I don't have a ruler or a caliper that has 80ths of a millimeter on it. Decimals on a calculator is the way to go every time for conversions unless you are on the cad.

SOD will have to explain where his fraction comes from, I make it 6858/160, which is of course the same as 3429/80

Log tables, I'm not surprised the previous contributor's boss raised an eyebrow, I'd have raised the roof, slow and more chance of error. I remember a chap in the design office doing sums on a mechanical contraption that you set up and wound the handle till it went ping, then wound it back one turn. It worked, but as soon as he got a calculator it went in the scrap. I'm surprised no-one has bemoaned the demise of the saggar makers bottom knocker

[CirclipParticipant @circlip]

Yep Duncan, I remember using the hurdy gurdy for doing circlip design calcs and as far as logs were concerned, plenty of class 365s and 465s DMUs hurtlling about with stainless exzorsts.

Regards Ian.

[duncan webster 1Participant @duncanwebster1]

I'm not suggesting using logs gives the wrong answer, but it takes longer for no benefit, and as it takes longer it costs more

[Michael GilliganParticipant @michaelgilligan61133]

Posted by duncan webster on 17/08/2021 14:46:06:

But I don't have a ruler or a caliper that has 80ths of a millimeter on it. Decimals on a calculator is the way to go every time for conversions unless you are on the cad.

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I presume that you write in jest, Duncan … But just in case: The point was that the fractional calculation is exact, and the decimalisation thereof is only done on the answer.

MichaelG.

[JasonBModerator @jasonb]

Posted by duncan webster on 17/08/2021 14:46:06:

But I don't have a ruler or a caliper that has 80ths of a millimeter on it. Decimals on a calculator is the way to go every time for conversions unless you are on the cad.

Look at the top left of the screen on Michael's first image it has the metric answer to 3 decimal places not just the 80ths

[Ramon WilsonParticipant @ramonwilson3]

Posted by Michael Gilligan on 17/08/2021 13:49:11:

You must try harder, Dave

Here is the calculation, in fractions:

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.

The fractional answer is correct

MichaelG.

Steady guys – that (and the other replies) seems a long way to get to the answer

1 1 / 1 6 + 1 x 2 5 . 4 = (thirteen inputs on a conventional basic calculator) amazingly gives the same answer – 42.8625

Ah but of course I know you want to show all that mathematical prowess you all possess to an old numbskull like me. Impressive of course but neccessary – hmmm not so sure on that – I'll bow out here me thinks.

Great topic and good comments though

Tug

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Ramon Wilson on 17/08/2021 16:39:36:

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Steady guys – that (and the other replies) seems a long way to get to the answer

 

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Sorry if it wasn’t self-evident, Tug

The working that I showed is the way the Calculator does it … That listing is available at the touch of the button at top right of the display.

Please see my post at 08:51:28 this morning.

MichaelG.

Edited By Michael Gilligan on 17/08/2021 17:03:31

[JasonBModerator @jasonb]

And Less input from you too Michael as there is no need for the / and + in Tugs example so just 11 buttons to press

Edited By JasonB on 17/08/2021 17:06:07

[SillyOldDufferModerator @sillyoldduffer]

Posted by Michael Gilligan on 17/08/2021 13:49:11:

Posted by SillyOldDuffer on 17/08/2021 12:03:49:

[…]

All fraction calculators suffer to some degree from this inaccuracy, though the more sophisticated versions do far better than simple minded digital calipers. Michael's example is close: his calculator (and Nick's) both give 1¹¹⁄₁₆ x 25.4 = ³⁴²⁹⁄₈₀. So does mine. However, the real answer is ⁹⁶⁵¹⁷⁷⁶⁹⁵¹⁴⁰⁸³⁹³⁷⁄₂₂₅₁₇₉₉₈₁₃₆₈₅₂₄₈. Don't panic, ³⁴²⁹⁄₈₀ is an excellent result, the error being only -²⁷⁄₁₁₂₅₈₉₉₉₀₆₈₄₂₆₂₄₀.

Highlights a serious problem with fractions because the level of inaccuracy of each calculation depends on the individual ratio and on the number of display digits available. […]

.

You must try harder, Dave

…

The fractional answer is correct

MichaelG.

Oh no, one of us must be wrong! Surely not me?

Sadly it's true, I've cocked up AGAIN!

Sorry,

Dave

PS Nurse says bed with no supper tonight…

[Nigel Graham 2Participant @nigelgraham2]

There's much shorter approach by calculator than that shown; as Tug describes and I would do it:

1) Divide 11 by 16.

2) Add 1.

3) Multiply by 25.4.

= 42.8625

OR….

1) Divide 27 by 16. (27 = 16 + 11; simple enough for mental arithmetic more rapid than Steps 1) and 2) above.

2) Multiply by 25.4.

= 42.8625

On some calculators you may need use the equals sign at the appropriate point in either method.

A waltz and a two-step! Not sure what the photographed umpteen-step example is on that theme… More like Strictly Come Dancing.

[Author]

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