Slide Rule to convert dimensions scale to scale?

[Porkscratching]

5 minutes ago, Hroth said:

Apparently an "E6B", very special purpose!

 

https://en.wikipedia.org/wiki/E6B

Very interesting!

ps I never noticed that Mr Spock used one, amazing what you find out ! 

[Dave Hunt]

In the RAF an E6B was a standby compass. The circular slide rule type device used for navigation calculations was called a Dalton computer. 

 

Dave

 

Correction - the standby compass was an E2B. Old age catching up......

Edited August 18, 2019 by Dave Hunt

[Enterprisingwestern]

 

The Mears range of calculators is still the way to do central heating calculations in my world!

 

https://mhmear.co.uk/

 

Mike.

[Mark]

19 hours ago, Porkscratching said:

I recall a post somewhere on the forum, not particularly recently, suggesting use of a slide rule to make simple conversions or take dimensions from one scale to another..

For instance, I would like to take dimensions from a 7mm to the ft. model or drawing, and convert them with as little maths as possible to 10mm to the ft. scale... Now it was suggested this could be done by simply setting a slide rule and reading off the result..this sounds like it'd be ideal... Any idea how you'd do this ?.

If it's a "goer" I can doubtless get a slide rule off evilbay for pennies !

Also are all slide rules marked the same ?

How about drawing a right angle triangle. For the base draw a line 300mm long which is equivalent to 30’ in 10mm scale. On the vertical axis draw a line 210mm long which represents 30’ in 7mm scale. Draw a line linking the end of both lines (The hypotenuse of the triangle). You could divide the 7mm line into 30 7mm increments and the 10mm line into 30 increments of 10mm. So all you have to do then is look for the size on your 10mm line that you want to convert and then draw a vertical line which intersects the hypotenuse. At this point draw a horizontal line and it should intersect the 7mm scale axis at the equivalent 7mm scale of your 10mm dimension. So for example 100mm on the 10mm scale should come out at 70mm on you 7mm scale. You can do the same in reverse to convert the other way.

 

Regards

 

Mark Humphrys

 

 

[Porkscratching]

More good suggestions gents !  Nice to see there's a firm who still make simple 'analogue'  devices like the Mears range..

[dhjgreen]

11 hours ago, Hroth said:

 

Looks like a British Thornton* to me.

 

We started with log tables, progressed to sliderules and then one day, there was a small box on the teachers desk with glowing numerals, and a numeric keypad.  He said "This is the future, you'll never have to worry about sliderules again..."

 

As well as the BT which I still have, I've a cute little circular one that I picked up when a stationers shop was closing down.

 

* Perhaps not, or maybe a more upmarket one, the cursor is a bit fancier in your photo!

 

Correct, British Thornton.  The same model as the one I had over 40 years ago.

[Porkscratching]

3 minutes ago, dhjgreen said:

Correct, British Thornton.  The same model as the one I had over 40 years ago.

 BT seem to be one most favoured and used, a bit like Moore and Wright for mics and measuring kit..

I look forward to playing with mine when it arrives..

[JeffP]

Saw my first calculator circa 1967, made by a physics teacher mad on electronics.

It was about 10" x 8" x 2" with glowing red digits, and it cost loads and ate batteries.

 

Edited August 19, 2019 by JeffP

[Porkscratching]

Seem to recall my mum bringing one home from work probably about 1970ish. the display had tiny little dim red digits...

[dhjgreen]

30 minutes ago, JeffP said:

Saw my first calculator circa 1967, made by a physics teacher mad on electronics.

It was about 10" x 8" x 2" with glowing red digits, and it cost loads and ate batteries.

 

I made one about then too; nixie tubes (neon) and thumb wheel switches to set the 2 variables, an inverter to get the high voltage for the nixies was the big power drain.

 

 I also made a geiger counter using decatron tubes about then too. Anybody remember decatrons?

[Enterprisingwestern]

17 minutes ago, dhjgreen said:

 Anybody remember decatrons?

 

Captain Scarlet used to fight them?

 

Mike.

[sharris]

On 18/08/2019 at 13:55, ikcdab said:

I can't think how a slide rule would do this...

 

If you can use a slide rule to multiply by 1.4286 (i.e. 10/7 to 4 decimal places - that may be more places than you need) then you can do it. Multiplication is one of the standard uses for slide rules. 

 

[Dunsignalling]

22 hours ago, Porkscratching said:

I'll certainly check out the various scale rules, as you say 10mm is a fairly well used scale and you'd think they'd cater for it !

As they do seem to have a use in all this, I got a British Thornton slide rule from ebay a bit earlier for a fiver, so be interesting to have a play with that too, thanks to dhjgreen for the hints on how to apply it..!

If you are clever enough to use a slide rule (I never properly got the hang of it before calculators came along), you should be clever enough to scale stuff off to 10mm in your head.  

 

Wasn't that the whole point behind the invention of the decimal system?

 

John

Edited August 19, 2019 by Dunsignalling

[sharris]

Assuming that the purpose is to measure off distances on a 7mm scale diagram and scale them up to 10mm  the obvious and quick solution would be to take a standard ruler with your preferred graduations and photocopy it onto acetate at 70% scale to make a conversion ruler.  

 

You might need to do a few trial runs at settings around 70% in case the photocopier is a bit off. 

 

[Hroth]

With sliderules, we were told you had to have a rough idea of the quantities you were dealing to interpret what you were seeing at the cursor.  I always thought of using a sliderule as guided guessing...

 

My first pocket electronic calculator, with tiny red LED display (as basic as they came), could be persuaded to divide by zero!

[Porkscratching]

As i understand it, the result you get with a slide rule gives you a number and assumes you'll know the magnitude of the answer, put simply if you got say 750 you'd likely know by the context if it was going to be 7.50 or 75.0 

The little chart ickdab kindly provided earlier makes a handy conversion scale (or ruler if you like ) which I've been using,  thanks for all the great input and suggestions here gents..

Edited August 20, 2019 by Porkscratching

[dhjgreen]

2 minutes ago, Porkscratching said:

As i understand it, the result you get with a slide rule gives you a number and assumes you'll know the magnitude of the answer, put simply if you got say 750 you'd likely know by the context if it was going to be 7.50 or 75.0 

Correct and, if the calculation was especially complex, work out the correct powers of 10 separately.

[David Foulkes]

On 18/08/2019 at 22:49, Porkscratching said:

I recall a post somewhere on the forum, not particularly recently, suggesting use of a slide rule to make simple conversions or take dimensions from one scale to another..

For instance, I would like to take dimensions from a 7mm to the ft. model or drawing, and convert them with as little maths as possible to 10mm to the ft. scale... Now it was suggested this could be done by simply setting a slide rule and reading off the result..this sounds like it'd be ideal... Any idea how you'd do this ?.

If it's a "goer" I can doubtless get a slide rule off evilbay for pennies !

Also are all slide rules marked the same ?

Any slide rule intended for use in normal science/engineering calculations will have various scales on it, but the underlying principle is that all are logarithmic.  The rule makes use of the fact that Log (a x b) = Log (a) + Log (b). 

Anyhow, to get to the matter in question, you'll need to make use of the C and D scales.  C will be on the bottom of the sliding portion and the D scale will be directly below it on the body of the rule.  If you want to be able to measure dimensions off, say, your 7mm scale drawing and use them to construct a 10mm scale model, then start by positioning the hairline on the sliding cursor (The transparent thingee that slides up and down the rule) directly over 7 on the D scale.   Now move the slide so that 10 on the C scale (located at the RH end of the slide) is directly under the hair line as well.  Now you can make a measurement on your drawing with a standard metric ruler, or pair of digital calipers or whatever.  Let's say you measure a feature on the drawing is 23.8mm long.  Move the cursor so that the hairline is directly over 238 on the D scale.  The hairline will also be directly over the 'equivalent' measurement on the C scale.  I make it 340, so a bit of common sense tells you that the answer is 34.0mm.  As an earlier poster has pointed out, a slide rule has no decimal point, so you need to estimate the 'order of magnitude' of the answer.  i.e. where to put the decimal point.  If you slide the cursor to the left hand end of the D scale you will see that 1000 on the D scale corresponds to about 1428, or a smidgen under 143, which corresponds to 1.43286, which is 10/7.  Effectively you're using the slide rule to multiply any measurement on your 7mm scale drawing by 10/7.  The annoying part comes when you have to deal with a measurement which falls between about 78 and 90, or 7.8 and 9.0, or.....  These measurements fall on the D scale where there is no part of the C scale directly above it.  If you have a slide rule like mine you can see that the C and D scales both have little extensions to 9 on the left and 112 on the right, but for those rogue numbers in between there's nothing for it but to align the cursor over 7 on the D scale and shove the slide to the right, so that the 1 on the LH end of the slide is aligned over the 7.  Now you can read that e.g. a measurement of 84mm on your drawing corresponds to 120mm on your larger scale model.  

One way to avoid the necessity to shuffle the slide is to make use of the A and B scales.  These scales are the same as C and D, but half size, so each scale runs from 1 to 100, instead of just 1 to 10.  The up side is that you can avoid needing to shuffle the slide, the bad news is that resolution is now only half as good.

Many years ago I used to use my slide rule to convert measurements taken from a 1:48 scale drawing for use on a HO scale model.  It was just a matter of aligning 871 with 48.  It really doesn't matter which number goes on which scale, so long as you're consistent.  The only complication is that if, in this case, 48 on the D scale is aligned with 871 on the C scale, then measurements taken off the drawing are entered on the C scale using the cursor and the equivalent measurement for the HO scale model are read off the D scale.  If you think about it, you'll see why this is so.

As you can probably grasp from the foregoing, it's simple enough, but still a bit of faffing about, which is why I tend to use an electronic calculator these days.  For a case like yours, I'd just calculate the value of 10/7 and store it in the calculator memory.  Enter your measurement, then press X M and the measurement for your larger model flashes onto the screen. 

Happy calculating.....

[Porkscratching]

That's brilliant David! I shall copy and save the above, I will be referring to it in detail, (many times no doubt!)

I do like the idea of keeping the use of these 'outdated' instruments alive, I've got a couple of old micrometers which I've used on occasions ( particularly when rebuilding an old gearbox, but that's another story)

Anyway thanks again for that comprehensive walk through, much appreciated!

[JeremyC]

Slide Rule, also known as an Engineer's Guessing Stick.

I've still got mine somewhere.

Edited August 20, 2019 by JeremyC

[Guest CLARENCE]

Why would you want to use a slide rule anyway? I remember using one in my teens as an apprentice  draughtsman, and hated the things. They've been well and truly replaced by (much more accurate) calculators, which are vastly easier to use!

[Porkscratching]

Somehow I still rather like the idea of a physical object with numbers stamped on it that can be simply read off against a scale, but what can I say....I'm the kind of bloke who likes old steam engines...

[rab]

I'm sure you've heard the one

about the constipated mathematician?

[Enterprisingwestern]

33 minutes ago, Porkscratching said:

Somehow I still rather like the idea of a physical object with numbers stamped on it that can be simply read off against a scale, but what can I say....I'm the kind of bloke who likes old steam engines...

 

Likewise, some of us prefer books to electronic methods of storage.

 

Mike.

[rab]

1 hour ago, Enterprisingwestern said:

 

Likewise, some of us prefer books to electronic methods of storage.

 

Mike.

But if they're stored digitally you don't get the complaints

from SWMBO about how much space they're taking up.