[Semper Vaporo]

Posted By David Leech on 25 Jul 2012 09:17 AM
Posted By seadawg on 25 Jul 2012 07:20 AM
WOW, that 7/8 stuff looks really big!


Well, doesn't that mean it's 7/8 of the real thing.
So the real one is only just a little larger than the one in the photo!
All the best,
David Leech, Delta, Canada


Hee hee hee... yeah!

I know you know better, David, but it points out one of my pet peeves... not only can nobody really agree on what "G" scale is (especially small vendors and advertisers!), no one can really agree on the nomenclature of how to specify or designate a scale.

Old timers (and those that learned from them) often use just one number and imply in their usage that the number is the number of inches (or fractions thereof) per foot of the real thing (so 7/8 means 7/8's inch per foot), which is a scale of 1:13.7 (approx.) and some people would refer to it that way, and others would specify it as 1/13.7 (note the slash instead of a colon).

I ALWAYS have to stop and think about the "real" scale when I see something specified as a single number leaving the "Per something" to the imagination. Often the only clue is if they include a unit of measure with the number... thus "7/8 scale" is just a wee bit smaller than the real thing, but "7/8-s inch scale" is 1/13.7 of the length and 1/13.7 of the width and 1/13.7 of the height of the real thing, which is 1/2579th of the real thing.

I also think it is really weird when the number specified is in a Metric unit, but the other number is in English units... like "78mm scale", which means 78mm per foot, which others would list as 3 inch scale and others would say 1/4 scale or 1:4 scale. It so much seems like fruit salad (i.e.: apples and oranges).

And note that scale is always specified in linear measurements (length or width or height) not in volume measurements, thus a 1:2 scale ("6-inch scale") model is 1/8 the volume of the prototype.

And per the subject of this thread, a 7/8" scale is pretty big compared to the other "G" guage stuff, being a model of an prototype that ran on 2-ft gauge track... but a 7/8 scale would be much too large to fit in most gardens or on G-gauge track, unless the original gauge was 2-inches!

 

[Semper Vaporo]

Posted By DKRickman on 26 Jul 2012 04:49 AM
And note that scale is always specified in linear measurements (length or width or height) not in volume measurements, thus a 1:2 scale ("6-inch scale") model is 1/8 the volume of the prototype.

That's accurate enough, but why bother to mention it. Linear scale is what you need in order to build a model, while the volumetric ratio is pretty much immaterial unless you need to know the volume of a container - and I submit that if you need the volume for some practical purpose, you're probably not as interested in scale modeling as in making something do a job. Also, most people find it a lot easier to calculate a square or cube of some number, rather than a square or cube root!

I, and I know others do too, perceive Volume more than Linear dimension. This is why the difference between 1:32 and 1:29 is so glaring to me and others. There may only be a 10-percent difference in the linear dimension, but it is a 30 percent difference in volume.

I attend a Thresher's reunion every year and there is a fellow that has a 1/2 scale (his nomenclature) Case Traction Engine as well as the prototype it is a model of. In my view the model appears a lot smaller than just 1:2 scale. It is very definately much smaller... being only 1/8th the volume.

Granted, when designing/building a model you are working in linear dimensions and so that is all you are concerned with, but the result still "LOOKS" smaller than the stated scale.

 

[Semper Vaporo]

Oh, and one more note to keep in mind... the specified scale is not used to calculate the difference in weight. A 1:20.3 scale locomotive is not 1/20.3 of the weight of the prototype, nor will it have 1/20.3 of the tractive effort. An exact model would be 1/8365.427 of the weight and that number would have to be taken into account to calculate the tractive effort, but the tractive effort would probably never even be 1/8365.427 of the protytype, because the physical properties of the materials do not necessarily scale in either linear or volumetric ways. Temperature and pressure do not scale at all. (A prototype steam locomotive that had a 180 pound boiler pressure would not work all that well at either 1/20.3 or 1/8365.327 of it [8.9 lbs or 0.02 lbs, respectively]!)