3 1/2, 5 and 7 1/4

Cboomf · 3 1/2, 5 and 7 1/4

Does anybody know why common model rail gauges in the UK are 3 1/2", 5" and 7 1/4" ?

Just that at the local model engineering society nobody knows, so am throwing the question open ...

bessytractor

its just what became popular at the time. Everyone standardised on a gauge that matched the scale.

Graham-Jilly

they are the same here in Aus

bessytractor

they are mostly the same worldwide.

The east coast of the US (I think) uses 7 1/2" and 4 3/4" gauge perversely, somewhere the extra 1/4" got lost mid Atlantic!

Titan

Not quite, the scales (for standard gauge at least) do not work out exactly:

3 1/2 = 1/16.143 full size (0.743 inches to the foot)
5 = 1/11.3 full size (1.06 inches to the foot)
7 1/4 = 1/7.79 (1.54 inches to the foot)

I suspect that many modellers round up, ie build to 3/4, 1, and 1.5 inches to the foot, and adjust the frame spacing etc to suit, otherwise scaling drawings down from full size becomes tricky!

In America:

4 3/4 = 1/11.894 (1.009 inches to the foot) so pretty good for 1 inch scale.

7 1/2 = 1/7.533 (1.59 inches to the foot)

I think it was all an attempt to have a gauge in reasonably round figures, and a scale in reasonably round figures, but with a full size gauge of 4' 8 1/2 ", round figures all round aren't really going to happen!

bessytractor

blast these rivet counters

some of the best engines I have ever driven were not by any means scale models

dampfmaschinenjoe 1967

Hi there,
Here´s my trial to explain the different measurements:
These measurements are not only intreresting for "rivet counters". The club track you are visiting has a special trackwidth. 3.5", 5"and 7 1/4 " at most standardized tracks around central Europe. The size of the rolling stock depends on the use of these track measurements for narrow or standard gauge. 5" narrow gauge means an engine size of 1:6 (metric)and the same in standard gauge 1: 11,5 (metric) .
So not only the trackwidth is important also the prototype of the engines and rolling stock I own two vintage Gauge 1 locos which are nearly 1:32 on 45 mm trackwidth, my other six engines have narrow Gauge IIm, that means 1:22,5 on 45 mm rails. They are a lot bigger than my Gauge 1 engines.

cheers Joe