Posted By Steve Stockham on 01/12/2009 5:49 AM
Well, here we go again... I'm sure that we have managed to intimidate some of the newbies with all of the ratios and gauges (out to the nth decimal...) Getting back to the gist of this little deviation from the thread, the point 3 in 1:20.3
doesn't refer to the gauge of the track being represented. As to the rest, F is a legitimate scale being represented by the ratio of 1:20.32 as per NMRA standards and bringing the thread back to the original topic, that 2-6-6-0 is
gorgeous!!
That sir I can not agree with.
The uppercase 'F' is in fact nothing more than an arbitrary label that was chosen to use instead of actually stating the scale ratio.
Further more, as happens many times things sort of happened in reverse. In the case of what eventually came to be labeled 'Fn3' scale (1:20.32) under the
NMRA - General Standard Scales S-1.2 (Approved July, 2004) (Remarks Column - see note 2, which references #1 Gauge track (i.e. 45mm)).
Originally began with modeling 3-foot narrow gauge prototypes on #1 Gauge model track (i.e. 45mm gauge). If you divide the gauge of the prototype track (i.e. 36"), by the gauge of the representative model track (i.e. 45mm, converted to its equivalent inch measurement) and round the result to two decimal places, the result is 20.32, thus the scale ratio is 1:20.32 and that is what the letter 'F' is being used to represent.
The next step in the sequence, was the NMRA decided to include what has generally come to be referred to as 'large scale', in their Standards. Since in most cases of their standards the base scale designation (i.e. in this case 'F') represents that particular scale ratio (i.e. 1:20.32) as it relates to the prototype Standard Gauge track (4'-8 1/2" gauge) and its associated equipment. This would result in a model track gauge of 70.62mm (2.781") using the defined scale ratio of 1:20.32.
Addressing the usual convention used when discussing the suffixes appended to the base scale designation. The lowercase letter 'n' denotes the fact that the scale ratio is being used to represent a prototype track gauge that is narrower than the Standard Gauge (i.e. 4'-8 1/2") prototype. Next the numbers following the lowercase alpha suffix, express the prototype track gauge being represented in either whole feet, or whole inches (e.g. n3 = 3-foot gauge, n30 = 30-inch gauge).
Additionally, addressing a point that Dean raised above, the case of modeling what is generally referred to as Broad Gauge (i.e. railroads where the prototype track gauge was larger than 4'-8 1/2"). If this were to be included within the standards, to maintain consistency I would think the proper lowercase alpha suffix to use would be a lowercase 'b', and continue to use the convention of expressing the track gauge in whole feet or whole inches. Thus a Broad Gauge prototype of 5-feet would be expressed as 'Fb5', and a Broad Gauge prototype of 5 1/2' feet would be expressed as 'Fb66'.
In so far as your statement...
"Getting back to the gist of this little deviation from the thread, the point 3 in 1:20.3
doesn't refer to the gauge of the track being represented."
You're correct, in so far as the '.3' doesn't refer directly to the track gauge, it refers to the scale ratio, but the scale ratio defines the gauge dimension of the model track, and the level of precision that the model track, and any models of equipment, adheres to in its representation of the prototype. Because the scale ratio defines the linear measurement that represents one scale foot (i.e. 12 / 20.32 = 0.59" (approx. 9/16")). Note, some individuals also round this value to the nearest tenth of an inch (i.e. 0.6) so they can use an engineering rule graduated in tenths of an inch.
Finally, I don't agree with this aversion to discussing the concept of scale ratios and proportion with individuals new to the modeling hobby realm. Since it's the foundation that all of what's done in modeling rests upon. Once those concepts are understood all the rest of the alpha-numerical soup they'll encounter falls in place rather nicely, with a little explanation of what the various designations represent.
