Scale gauges

[merlinParticipant @merlin98989]

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

[merlinParticipant @merlin98989]

[not done it yetParticipant @notdoneityet]

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

Good enough for me.

[Former MemberParticipant @formermember19781]

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[Howard LewisParticipant @howardlewis46836]

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

[Former MemberParticipant @formermember19781]

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[SillyOldDufferModerator @sillyoldduffer]

Posted by 34046 on 21/08/2019 19:47:56:

…

7,25 inch locos and rolling stock are built to a scale of 1.5 inches equals 1 foot.

…

Bill

 

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

[Former MemberParticipant @formermember19781]

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[Former MemberParticipant @formermember19781]

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[Former MemberParticipant @formermember19781]

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[JasonBModerator @jasonb]

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.

[Ron ColvinParticipant @roncolvin83430]

Posted by SillyOldDuffer on 22/08/2019 10:44:15:

Posted by 34046 on 21/08/2019 19:47:56:

…

7,25 inch locos and rolling stock are built to a scale of 1.5 inches equals 1 foot.

…

Bill

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

With passenger hauling model locomotives it is the gauge that is important, the scale is nominal. If someone is a stickler for having a correct scale/gauge ratio, they can tweak the scale accordingly. With small scale scenic model railways the scale is generally kept constant, and it is the gauge that is adjusted by the purist.

[Former MemberParticipant @formermember19781]

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[Perko7Participant @perko7]

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.

[Ron ColvinParticipant @roncolvin83430]

Posted by 34046 on 22/08/2019 12:40:53:

That is interesting Ron

i always understood back along when I spoke to Reeves that drawings for locos were drawn to scale ie 0.75 inch for 3.5 gauge, 1 inch for 5 gauge and 1.5 for 7.25 gauge ?

Is this correct please ?

Bill

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".

[John BaguleyParticipant @johnbaguley78655]

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

[Neil WyattModerator @neilwyatt]

Posted by John Baguley on 22/08/2019 16:19:40:

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.

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

[BazyleParticipant @bazyle]

Posted by Neil Wyatt on 22/08/2019 16:35:32:

Logic is in short supply with regard to gauges and scales in railway modelling..

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.

[Ron ColvinParticipant @roncolvin83430]

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.

[Former MemberParticipant @formermember19781]

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[Brian GParticipant @briang]

Posted by 34046 on 22/08/2019 18:47:22:

…

And yet they waited until 1893 before they brought out their 0 gauge loco for some unknown raeson ?

Bill

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&quot at 1:32 (G1MRA standard 10mm/ft is 1:30.5)

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

III 89mm (3 1/2&quot at 1:16

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

VII 184mm (7 1/4&quot at 1:8

X 184mm (10 1/4&quot 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

[IanTParticipant @iant]

Hi Merlin,

I'm not sure anyone has given you the fully correct way to think about "scale" – but I've only very quickly scanned the thread replies. But here's my version of it…

"Scale" is very simple and relates to the relationship between the original prototype's 'gauge' and the gauge you intend to use for your model. The model track gauge can of course can be anything you want it to be – although most folk use one of the various track 'standards' mentioned. However, assuming you are modelling an actual prototype – then it would have had a fixed gauge – be that standard, broad, metre or one of the many varied narrow gauges…

I model standard gauge prototypes (4ft 8.5" ) on 2.5" gauge tracks – so the scale ratio is 1:22.6 – that's 56.5" divided by 2.5". However, if I was modelling a 2ft (24" ) narrow gauge engine on 2.5" track (as some N2.5GA members do) – the scale ratio would then be 24" divided by 2.5" – or 1:9.6.

So the 'gauge' is the distance as measured between the inside edges of the rails and the 'scale' is the ratio between the full size gauge of the engine or stock you are modelling and the model track gauge you intend to use.

However, for ease many of the standard "gauges' use approximations of the scale…e.g. 1" scale for 5" tracks… These are really just convenient rules of thumb…

In G3 we are lucky to have a pretty good match for our scale/gauge. Our approximations are either 17/32nd or 13.5mm (per foot) and as it turns out these are very near the actual scale ratio of 1:22.6. Pre-CAD – I used 13.5mm as a scale converter for convenience – but these days I just draw things full-size and scale down by a factor of 22.6 – very easy to do in CAD.

Regards,

IanT

Edited By IanT on 22/08/2019 21:43:10

[Paul LousickParticipant @paullousick59116]

The scale of your model engine (ratio between the the original, full size engine to the one you are building) does not have to be exactly the same as the scale of the rails (ratio between the width between the full size rails to the model rails).

Rail gauge is simply the distance between the 2 rails. Within reason, an engine can be re-gauged, to run on different width rails by changing the distance between its wheels.

eg. In Australia the small locos used in our cane growing fields are built to 2 foot gauge rail standards and must comply with government regulations to operate, even if they are used on private property. (laws brought in place because they also travelled across public roads). This is expensive and requires a lot of paperwork. If the locos are re-gauged by changing the width between the wheels to 1'-11.7/8" they no longer comply with the government standards and can operate without restrictions on private property.

Paul.

[merlinParticipant @merlin98989]

I think the modern expression is 'WOW!'

Thank you all for taking the trouble to reply.

Abutting the riverside public footpath between Shiplake and Henley is a large house and garden with a private railway running through it. The station and, so far as I remember, other model buildings are easily visible.

Is this 'park railway' likely to be 7 1/4" gauge?

Thanks.

[IanTParticipant @iant]

If it is Fawley Hill that you are thinking of Bill – this is a full-sized standard gauge railway on the McAlpine Estate. It's not open to the Public per se – but I've been several times as part of an invited group (I'm a member of several model railway societies).

I don't think there is a 7.25" railway there – the only one I know of in the area would be Pinewood, between Crowthorne and Wokingham (Berks). They have public running days on the third Sunday of the month during the summer and they also do a Santa Special at Christmas (much enjoyed by my Grandchildren). If you live near Henley, then it's not too far for you to go.

Regards,

IanT

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