Choosing Scale and Gauge

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A Scale and Gauge for the C&BFT
Which O scale?

A Scale and Gauge for the C&BFT


Over the years I imagined I would be building the Corinella and Blackwood in HO scale, using N (9mm) gauge track, commonly known as HOn30. I even have some track and a few items of rolling stock. Building in HO has many advantages. Foremost is the huge range of kits and assesories for just about any item you can imagine. Scenicing an HO layout would be the most straightforward of any scale. And I could use N gauge mechanisms for locos, or so I imagined.

When I decided to take up the hobby seriously again, I started to join Yahoo groups on the web. A great way to get advice. Quickly I was befrended by another Melbourne modeller, John Dennis. John is well known for his Dutton Bay layout, an HOn30 layout that has been around for a number of years. John is in the process of converting the Dutton Bay from an exhibition layout to a home layout. The Dutton Bay is to have timetable operation and card forwarding so it will operate "just like the real thing".

Great, just what I wanted for the C&BFT. I explained to John the C&BFT was to be a large, operations-orientated layout set in the 1920's. Alarm bells rang. John explained that very few modellers had managed to get any number of good-operating steam loco models in HOn30. The mechinisms were just not up to it. Those that did were highly skilled modellers, something I was not! He explained the Dutton Bay, and many other layouts in HOn30 got by using diesel mechanisms, with freelance diesel bodies. For that reason the Dutton Bay was set in the 1970's. Diesels are right out of period for the C&BFT.

John explained that he was seriously looking at modelling in O scale using HO (16.5mm) gauge track, and suggested I look at it too. I did and liked what I saw. The rolling stock had that certain mass, and a layout could fit into much the same space as an HO layout. A 25' Puffing Billy louvre van in O scale is about the same size as a 40' American box car in HO scale. Being narrow gauge, my 6 to 8 car trains would look more prototypical than similar length trains on an HO standard gauge layout. There are plenty of large, HO scale operations orientated layouts around the world, and the C&BFT in O scale would take up much the same amount of room.

There are disadvantages. Firstly buildings in O scale are much more massive, being double the length, width and height. Then there are far fewer building kits and other scenic items in O scale. But I am fortunate, in that buildings in the era and area I am modelling were both fairly small and not found in large numbers. I wasn't wanting to build New York City here! However I will have to give up plans for a port scene and broad gauge interchange.

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Which O scale?

One of the first things a newcomer to O scale finds out is that there are in fact not one but four O scales! Which one to choose?

British O scale: 1:43.5 (or thereabouts) or more properly 7mm:ft. Also used in France and some other European countries. Modelling narrow gauge railways using this scale and HO gauge track is usually referred to as O-16.5.

German O scale: 1:45 The most common European O scale. Modelling narrow gauge railways using this scale and HO gauge track is usually referred to as Oe.

American O scale: 1:48 Also known as 1/4 scale, as it is equal to 1/4" to the foot. Modelling narrow gauge railways using this scale and HO gauge track is usually referred to as On30.

Indian O scale: 1:50 OK maybe an exageration to call it "Indian", but at least one locomotive kit has been produced in this scale. It allows Indian modellers to get close to scale gauge track using 32mm gauge track when modelling their 5'6" broad gauge main lines.

We can safely ignore Indian O scale, it is not a popular scale for narrow gauge modelling! It is interesting to see what the prototype gauges scale out at using the three other common O scales. In the chart below I have shown the most common feet and inch gauges, and their metric conversions, and two common metric gauges.

Imperial Gauge
2'
2'3"
2'6"
3'
Scale Metric Gauge
600mm
610mm
686mm
750mm
762mm
914mm
O-16.5
1:43.5
(7mm/ft)
13.8mm
14.0mm
15.75mm
17.2mm
17.5mm
21.0mm
Oe
1:45
13.33mm
13.56mm
15.24mm
16.67mm
16.93mm
20.32mm
On30
1:48
(6.35mm/ft)
12.5mm
12.7mm
14.3mm
15.62mm
15.88mm
19.05mm

First thing to note is how close 16.5mm is to correct gauge for 750mm prototypes in 1:45 scale. 750mm happens to be a very common gauge in Germany, and 1:45 the German scale. Lucky Germans!

Secondly how much too wide of correct scale 16.5mm is for 2' gauge, in all scales. For this reason Americans have long had the scale/gauge of On2 using 12.7mm gauge track, while the Brits are increasingly using 14mm gauge track for their 2' models.

However HO gauge track is very close to correct scale for 2'6" prototypes in 1:48, in fact less than 4% too wide. In real terms this is just a fraction more than 0.7mm too wide, a measure I would find hard to note with my plain eyes. As the railways I want to represent were largely built in 2'6" gauge, this scale/gauge combination seems an acceptable compromise.

There is an argument that the correct gauge should be used, and that using fine scale standard will result in a better model. Dr. K.J. Walker is one who follows this argument, and models in 4mm scale, using 10mm gauge track to represent 2'6" gauge. He feels this is especially important as he also plans to model the Indian metre and 5'6" gauge railways, and wants to maintain the reletivity between the gauges. His arguments are expanded upon here.

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