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Conversion factor

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Eric Cox02/06/2010 09:44:01
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557 forum posts
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Can you tell me the conversion factors required to scale down from full size to scale size.
 
 Cheers Eric
drjohn02/06/2010 09:50:32
8 forum posts
Hi Eric
 
If you gave us a clue about what "scale" size you're talking about, then yes, it might be feasible to give you a sensible answer.
 
Basically, take the gauge of the full size you want to model (in inches) and divide it by the gauge you want to scale it to (in inches) and that will be your scale factor.
 
DJ

 

Edited By drjohn on 02/06/2010 10:02:07

Chris Trice02/06/2010 11:11:58
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Er... the answer is so obvious as to make me wonder if the question has been posed correctly. How big is the original in inches or millimetres? How big is the model you want to make in inches or milimetres? Divide the former by the latter.
 
If the original is 24ft long and you want to make a model of it 2ft long, the scale is 24 divided by 2 = 1/12th scale.
 
If you divide every full size measurement by 12, everything will scale correctly.
 
OR are you asking what scale various model railway gauges are?
IanT02/06/2010 11:19:42
2147 forum posts
222 photos
Hi Eric,
 
DJ is on the right "track" here - but of course - it depends on the prototype gauge e.g standard gauge, metre gauge etc. This question was asked a year or so ago. My answer then seemed helpful;
 
"... 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
Eric Cox02/06/2010 14:16:58
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557 forum posts
38 photos
Thanks for the replies. No, the answer isn't obvious otherwise I wouldn't have asked.
Let me put it like this. A full size loco has a driving wheel of 4' 6" Dia. I wish to make a 31/2" gauge model, How do I convert from full size to 31/2" size.
Is 31/2" the gauge of the track or is it 31/2" to the foot.
KWIL02/06/2010 15:56:52
3681 forum posts
70 photos
If the tracks is 3 1/2" and full size is 4' 8 1/2" that makes it 1/16 size, so 4' 6" diameter driver becomes  3  3/8" (3.375").  Is that straight forward enough?
Chris Trice03/06/2010 03:00:42
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1376 forum posts
10 photos
 
To recap. How big is the original in inches or millimetres? How big is the model you want to make in inches or milimetres? Divide the former by the latter.
 
Assuming  the rail gauge of the original is 56 1/2" (you've told us the wheel diameter but not the gauge) and you want the rail gauge for the model to be 3 1/2"....
 
56 1/2" divided by 3 1/2" = 1/16 scale (as KWIL indicated- technically very slightly smaller as not a whole number results)
 
Divide every full size dimension by 16 to get the model dimensions.
 
Again as KWIL indicates a 54" diameter wheel becomes (divide by 16) 3.375"
 
If the scale was 3 1/2 inches to the foot (the clue is in the wording - 3 1/2" of model represents 12" of fullsize), you'd have a model of a full size 60ft loco that come out at 17 1/2 ft long.
 
A bit big. 
drjohn03/06/2010 06:26:08
8 forum posts
Your sums are a bit out Chris - as kwil says, it's 1/16 scale so if it was a 60 foot loco in full size, it will come out as 45 inches in 3 1/2" gauge.  720 inches divided by 16 = 45
 
DJ
drjohn03/06/2010 07:07:46
8 forum posts
This really is a wunnerful forum - I'm not even allowed to edit my posts! Zero out of 100 for the forum designers.
 
DJ
 
C'mon, ban me moderators!

Edited By drjohn on 03/06/2010 07:08:18

Eric Cox03/06/2010 09:22:31
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557 forum posts
38 photos
Thanks Kwil, that's all I wanted to know.
Chris Trice03/06/2010 09:25:51
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1376 forum posts
10 photos
(cough)"If the scale was 3 1/2 inches to the foot ...."(cough)
Edited By Chris Trice on 03/06/2010 09:27:29

Edited By Chris Trice on 03/06/2010 09:28:01

KWIL03/06/2010 09:31:41
3681 forum posts
70 photos
Come on DJ, are you up to your usual "tricks" here as well?
drjohn03/06/2010 12:55:45
8 forum posts
Good heavens kwil, I can't think to what you are referring
 
I only came to this backwater because I was getting a load of dwindies from this site hitting my own site - don't worry I ain't staying!
 
Cheers
 
DJ

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