Wednesday, April 7, 2010

Scales and Gauges

I had intended to make my next entry an explanation of track cleaning but, instead, I have decided to examine scales and gauges and leave track cleaning until next time. 
Of course, most serious railway modellers will be aware of the various sizes available but, to the beginner, all of these letters and numbers can be a tad confusing at first. So I thought I would try and explain what they all mean and just what the difference is between Scale and Gauge. 
Oddly enough, the standards for model railway scales and gauges were established many years ago, using a combination of both metric and imperial measurements, and these still survive to this day. 
Scale: This is the ratio of the size of the model compared to its full size counterpart. Therefore, a 1:76 scale model is one seventy-sixth the size of the real thing. This equates to 4mm to 1ft or, in other words, every 4mm of the model is equal to 1 foot of the prototype - and here can be seen the curious mix of imperial and metric units I alluded to earlier. 
Gauge: This is the measurement of the distance between the rails and the standard gauge of full size track, which has been adopted almost worldwide now, is 4' 8½" Anything less than this is called narrow gauge while anything greater than this is known as broad gauge. As far as model railways is concerned the gauge of the track is generally given in millimetres and that which is most widely available is 16.5 mm. 
These definitions of scale and gauge are fairly precise, however, over the years the terms 'O gauge' and 'HO gauge' have become accepted as meaning both the scale of the models as well as the gauge of the track. Thus, in the UK, we refer to 'OO gauge' and 'N gauge' while, in Europe and North America, it is known as 'HO scale' or 'N scale.'
Now, whether you say 'N scale' or 'N gauge' it is really the letter or letters (O, OO, HO, N) that describe the size of the models. Therefore 'OO gauge' refers to models that are built to 1:76 scale (4mm = 1ft) while 'O gauge' refers to models built to 1:43 scale (7mm = 1ft).  
Anomalies do occur, as I will highlight in future posts when I examine the different scales in more depth. However, these are minor inaccuracies which are not so important in the greater scheme of things. 
The diagram below illustrates the the relative sizes of the more popular scales / gauges used by modellers today and I will look at each one, individually, in future blog entries.

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