Scale enlarge?

I know I've asked this before but I can't find the answer on here or even by googling!

If you have a scale drawing of 1/43.5 what do you multiply it by to get 1/22.5?
I know there is a formula for enlarging any scale to 1//22.5

mikey

A quick/easy method would be to double it up - gives 1:21.75 ☺

thanks Patrick! I shouldn't really have used that example!
there is a formula for enlarging any scale to 1/22.5. I just cant remember what it is

Think of it this way, Mikey. Take the dimension in scale A and convert it back to full size - multiply it by the scale A factor. Then take the "full size" dimension and convert it to the desired scale B- divide it by the scale B factor and voila. When I say "scale factor" I refer to the inverse of the scale, i.e. the scale factor for G is 22.5.

Putting the words into a mathmatical formula:
(Dimension in Scale A) X (Scale Factor A) / (Scale Factor B) = Dimension in Scale B

Example:
Convert 50cm in HO scale (1:87) TO G Scale (1:22.5)
50cm X 87 / 22.5 = 193.3cm

Simple math, actually (at least to an engineer).

Sorry Bill but surely 1 metre in 1/22.5 is 4.5 cms(the gauge of the track); so 50cms is 2.25 cms not 193 or am I missing something?

You missed something indeed. If you have a drawing in HO scale (1:87) and it depicts and object 50 cm long (in HO scale), the same object in G scale (1:22.5) would be 193.3 cm long.

For your example, you would multiply your 1:43.5 drawing by 43.5/22.5 (or 1.93) to convert it to G scale.

It's the right number, exactly its 193,5237.....

I use this link to convert scale, very usefull.

http://zmc78.com/les-techniques/convertisseur-echelle

Its in french, but follow some of the other link, nice idea for building things.

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Mikey if you are blowing up (enlarging....) drawings on a photocopier what I do is find something on the drawing that is scaled at 1 metre.

This is often the end view of a (metre gauge....) locomotive for example where the wheels meet the track.

Then I just enlarge it until I get a copy where this item measures out at exactly 45mm. Then I know the rest is all in scale.

Sometimes it's a bit of a guestimate with the percentage button on the copier and it takes a few goes. But it works in the end (once you find the right percentage figure) and you can make templates and paste the drawing on to wood or plasticard and cut out directly.

Bugger the maths....

An other way, more easy 1:87 is nearly 4 time smaller than 1:22,5.

So you could simply multiply by 4, you will have a scale of about 1:21,75

To be right on the scale the multiplier should be arround 3.87

And here a link with printable rulers at different scales, very practical as well :

http://fr.miniature-planet.com/scale_rulers.php

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By George, I think I've got it! Thanks guys; Carls suggestion is agreat one, but sometimes I'm just given a measurement from somebody elses drawing and i need the maths!!

mikey