Scale gauges

I dare hardly show my ignorance of this subject on this forum, but after years of rubbing shoulders with clever model railway engineers I have realised that I don't know what eg 71/4" gauge means. Is it the inside measurement between rails? Are the enginese and stock to 71/4" to the foot? Wikipedia tells me so much that I become confused.

Years ago I walked the footpath past the McAlpine house near Henley and could see the layout throught he trees; it is this gauge that interests me.

Thanks

First hit on ‘goggle’, from Ride on Railways, says distance between the rails, not scale.

Good enough for me.

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The gauge of the railway on the estate of the late Sir William McAlpine, at Fawley Hill, is the standard 4 ft 8.5 inch.

Howard

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Like Merlin I'm confused slightly by scale and gauge.

A scale of 1½" to 1' is 1:8 so standard gauge ( 4'8½" ) rail track should be modelled 7¹⁄₁₆" apart. Not that it makes any difference, but why jump to 7¼" or even 7½" as is popular in the USA?

Dave

Edited By SillyOldDuffer on 22/08/2019 10:45:12

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Then the whole scale thing goes out the window when you put narrow gauge models onto standard gauge based track widths

For example a 2ft narrow gauge model built to run on 7.25" track is approx 1/3rd scale or 4" to the foot.

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In Australia some 5-inch gauge models of standard (4ft 8-1/2inch) gauge locos are built to a scale of 1-1/16inch to get the scale/gauge proportions correct. Like model railways there are always compromises to be made, either for ease of construction, or to provide greater clearances, or because a scale reduction of actual dimensions would not provide sufficient tolerances or clearances for satisfactory operation. As others have said, narrow-gauge prototypes have different scale/gauge combinations. My model of a 3ft6inch gauge Queensland loco is built to 1-1/2inch scale to run on 5inch gauge track. It's not exactly correct, but I'm not going to use a scale of 1-27/64inch just to make it so.

I don't know where or when the adoption of 7-1/4inch gauge occurred in the UK and Australia, but that is what has become common use so we adjust the necessary dimensions to suit the 'slightly wider than scale' track gauge while keeping the rest of the loco to scale.

More likely that someone who has chosen to build with a correct scale/gauge ratio has decided to build a model of a prototype for which no drawings or castings are available. There is a lot of extra design/drawing work involved in producing a more authentic representative of a given locomotive from a published standard design. For example see the current ME series of articles by Doug Hewson on updating LBSC's pannier tank locomotive "Pansy".

The scales and gauges were standardised way back in Henry Greenly's day. Standard gauge locos in 2½" gauge were originall built to a scale of 1/2" to the foot but this later became 17/32" to the foot to give more accurate proportions. As stated, Standard 3-1/2" gauge is a scale of 3/4" to the foot and 5" gauge is 1-1/16" to the foot. The Americans etc. mostly use 4-3/4" gauge which is 1" to the foot. 5" gauge in the USA is rare.

It's often stated that the American 7-1/2" gauge came about because of a mistake by someone as they did originally use 7-1/4".

John

Logic is in short supply with regard to gauges and scales in railway modelling... probably because the strange standard gauge of 4'8.5" doesn't scale accurately to anything convenient.

7 1/2 and 7 1/4 are found in the USA, although 7 1/2 is more common.

One thing I don't understand is that, for example, both 3 1/2" and 5" gauge locos happily run on the same dual gauge tracks. So why not use 3 1/2" gauge flanges on 5" gauge models to get a more scale appearance? I can see this might be a step too far for 7 1/4" gauge, but surely they would get away with 5" flanges?

I bear in mind that large 3 1/2" wheels are bigger than small 5" gauge ones...

Neil

There is a sort of logic. Starting with G1 the gauges go up or down in a ration of root 2 so that the size of your model railway doubled or halved. That exact ratio was then rounded to a convenient, mostly imperial, dimension because most people didn't have a Babbage machine in their back room to do the scaling.
Also since G1 was started by those pesky Germans the Brits invented G2 to be 2in rail gauge which of course was logical at the time and is why 2 1/2 had to be called G3.

Then awkward people got in on the act and wanted things to be more accurate than cheap tinplate pressings so every size got split and some models can even be one scale at one end and another at the other.

The origin of having a set of standard gauges was introduced by a toy manufacturer in 1891 (Märklin ) . They were gauges numbered 1 to 5

Number 1 gauge = 45mm

Number 2 gauge = 54mm

Number 3 gauge = 67mm

Number 4 gauge = 75mm

Number 5 gauge = 120mm

The only one that has remained to its original dimension is gauge 1.

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According to NEM10 issued by MOROP the current large scale gauges and scales are:

0 32mm (No equivalent stated) at 1:45 (7mm/ft is 1:43.5)

I 45mm (1 3/4" at 1:32 (G1MRA standard 10mm/ft is 1:30.5)

II 64mm (2 1/2" at 1:22.5 (Gauge 3 in the UK)

III 89mm (3 1/2" at 1:16

V 127mm (5" at 1:11 (but we use 1:12 in the UK)

VII 184mm (7 1/4" at 1:8

X 184mm (10 1/4" at 1:5.5

Personally, I won't lose any sleep over these differences, I quite enjoyed riding on the RHDR today, and wasn't worried about 1/3 scale locos running on 1/4 scale track.

Brian