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Scaling Down

How to scale down to our sizes

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David Morley04/06/2009 17:05:26
1 forum posts
 What is the formular for scaling down from standard and narrow gauge, to model engineering gauges, i.e. 31/2" - 5" - 71/4"
IanT04/06/2009 19:18:07
2002 forum posts
212 photos
David the simplest way to get an accurate conversion is to take the ratio between the model track gauge that you intend to use, and the original (prototypical) track gauge. So for instance, standard gauge in UK is 4' 81/2" or 56.5" - so if you are modelling for a model track gauge of (say) 2.5" (Gauge 3) then you divide 56.5/2.5 and come up with a scale ratio of 1:22.6. If you then use this ratio (22.6) and divide it into 12 (i.e. 1 foot) you will arrive at a conversion scale of 0.53097" to the foot - in practice G3 modellers use either 17/32" or 13.5mm to the foot - which is slightly off this but convenient to calculate - but the principle remains true of any model you want to model - use the prototypical track gauge and compare it to the track gauge you intend your model to run on. IanT
Bruce Voelkerding02/04/2010 16:32:52
39 forum posts
David, I do the same with an extra feature (once advocated by K.Wilson in ME). I do my scaling in Excel. The first calculation is the scale factor as above by Ian. Then I just begin going thru all the dimensions in a tabular form. The first column lists the feature (i.e. Driver diameter), the second column lists the prototype value (i.e. I enter as a formula "=(4*12)+9.25" so I know I didn't mess up), the third is the the EXACT scale value (i.e. "=A6/C$2") , the fourth is the MODEL value (i.e. if the scale value is say 2.828 I might select 2.875 for various reasons). This way one maintains a single source of all the dimensions - very helpful 6 months into the project.
Paul Boscott03/04/2010 12:09:16
99 forum posts
21 photos
The answer that I got when asking a similar question was
3 1/2" gauge is usually modelled at 3/4" =1ft
5" at 1 1/16" =1ft (although some people use 1"=1ft)
7 1/4" at 1.5" =1ft
Somthing that I have done recently that has been realy usfull
(I am making a 1:12 scale model see
was to draw in the cad system the set of BA nuts and bolts at 1:1 then scale them by * 12.
Drawing  the model at 1:1 then when I reduce the model  by 12 the BA sizes will be in place and correct.
Stub Mandrel06/04/2010 19:58:06
4315 forum posts
291 photos
1 articles
I do much teh same thing as Bruce when planning a model. It works for wooden boats and even Daleks (but I haven't built that yet...)
On thing that's  hany about excel is you can tell it to display dimensions twice, once formatted as fractions - I usually choose 32nds or 64ths. It makes it easy to spot dimensions which conveniently scale to stock size. But don't mix exact dimensions and rounded ones or you get cumulative errors. I try to make unmachined sizes stock sizes and adjust the machined dimesions to fit. Saves a lot of extra machining.
Kerrin Galvin21/04/2010 11:40:29
44 forum posts
9 photos
Hi David,
  I have an Excel spreadsheet setup for calculating scale dimension. Just fill out the input cells & away you go. I got the orginal from an article some years ago in the Australian Model Engineer Mag. They still have it as a download on there web site, but I modified & added to it to allow conversion between imperal & metric as well. I setup the output cells so its to the nearest 1/64, if I remember rightly.
Let me know if you would like a copy.
Cheers Kerrin

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