Scale V's Gauge: A Brief History

I write and post this with trepedation.  I hope that it will go someway to answering the questions I recieve about scale v's gauge and what is closest to correct scale/gauge combination.  Hopefully by reading this we can see how we got to where we are today


What is the correct scale/gauge combination?  The answer is easy. Whatever works for you. In our hobby anybody can build anything they like.  If you wish to build a locomotive it must conform to certain standards as stipulated by agreement by the clubs around Australia and approved at the AGM of our governing body the Australian Association of Live Steamers (AALS).  These standards ensure the safety of the equipment and allow equipment from one club to operate on another club's track without issue.

Our hobby started in England over 100 years ago with Garden Gauge Railways operating on 'O' gauge (1 1/4") and G Gauge (1 3/4") track gauges.  With the availability of larger sized 2nd hand machinery after the First World war attention soon turned to making larger models with the intent of being able to drive them around a circuit of track.  With little or no modeling during the war years and a lack of plans it was convienent to simply scale up the existing plans by a factor of 2. 'O' gauge became 2 1/2" (17/32" : 12")  and 'G' gauge became 3 1/2" (3/4" : 12").  These were the two most popular gauges during the interbellum.  Prior and during the interbellum a prolific English writter, designer abd builder or small scale live steam models was LBSC or Curly Lawrence who's contribution cannot be overstated.  In 1922 " The battle of the boilers" begain which Curly later on by using boilers with firetubes and coal fired, unlike the previous use of commerical, spirit fired water tube boilers.  With the ceasation of conflict in 1945 thoughts one again turned back to one's hobby and with the advent of the Myford ML7 lathe in 1946 larger locomotives were possible for the average hobbist.

Using LBSC's plans and the work of others modelles again doubled up 2 1/2" gauge became 5" Gauge and 3 1/2" gauge became 7 1/4" gauge.  The reason that the 3 1/2" track went upto 7 1/4" and not 7" is because of its scale ratio of 3/4" :12" x 2 = 1 1/2" to the foot.  As the models were becoming larger and therefore smaller errors in scale became more obvious engineers decided to stick to a scale ratio based on the track gauges that were then in existence for 5" and 7 1/4".  This is where the maths comes in.  It is very simply really.  You take your track gauge (standard gauge = 4' 8 1/2" or 56 1/2" and divide that by the guage of the track you wish to run on. For 5" Gauge 56.5" / 5" = 11.3.  This figure is know as the scale ratio. In order to establish a length of 1 foot in the ratio we devide 12" by 11.3 = 1.0619.  The nearest practical full fraction is 62.5 thous or 1/16".  Therefore we can say our scale is 1:11.3 or 1 1/16" to the foot. You will note that this figure is very close to the 2 1/2" gauge (17/32) x 2 = 34/32 or 1 1/16"  The 7 1/4" did not get out so easily.  Again we take the track gauge 56.5" / 7.250" = 7.79. Once again we take 12"/7.79 =1.540" We simply then find the nearest easist practical fraction to use. 40 thou is reasonably close of 1/32 (32 thou). Therefore we use 1 17/32" : 12" for 7 1/4".


To recapitulate 1 1/16" : 12" is for standard guage locomotives running of 5" gauge track and 1 17/32" : 12" is for standard gauge locomotives running of 7 1/4" gauge track.  These scales apply mainly in the United Kingdom and other countries where English practice is followed eg Australia, New Zealand, South Africa and parts of Canada and North America.


In Australia before the advent of scale plans  and pocket caluculators it was found that scale rule could be used to convert the prototype drawings easily using a scale of 3/32" : 1" or 1 1/8" : 12". This gave slightly larger locomotive and rather than convert the tracks the gauge of 5" was retained in order to allow these locomotives the opportunity to operate on 5" gauge track. Although technically these locomotives are "Narrow Gauge" that is the track that they are operating on does not represent standard gauge using this scale, many fine and indeed magnificent examples have been built and continue to be built and is a scale/ gauge combination worthy of consideration. We find a similar simplfying in the adoption of 1 1/2" :12" in the 7 1/4" field.  The main reason for the adoption of this scale/ gauge combination was due to the prototype plans being drawn at   1 1/2" : 12".  This meant that the engineer could simply measure directly from the drawings thus saving a considerable amount of time in either producing drawings or rescaling plans.


Many other options are available for the model engineer. A Narrow Gauge locomotive operating on 2' Gauge track would be scaled at 2 1/2" : 12" running of 5" gauge track and would easily dwarf any standard gauge locomotive running on the same track.  Unlike most other hobbies that employ scale ratios, model engineers are fixed by the track gauge.  We simply ask what was the full size track gauge ( 2' for example) and what track gauge do we wish to run on (5" for example).  A simple calculation 5"/2 =2.5. This gives us scale of 2.5" :12".  If we all chose to model in a specific ratio of say 1 1/16" :12" the track gauge for a 2' gauge loco would be 1 1/16" x 2 = 2 1/8". In full size the larger the track gauge the larger the engine and the smaller the track gauge the smaller the engine. As we use our fixed track widith to give us of scale in miniature the smaller the track gauge of the prototype the larger the engine.


There are many other possible combinations for other broad and narrow gauge interests plus freelancing your own ideas.  No scale/ gauge combination is better or worse than another.  The choice is yours and yours alone.  Simple mathematics we tell you which is the closest scale to gauge ratio for standard gauge in various gauges. I hope this helps answer those many questions regarding scale/ gauge and what should I model.  FYI our plans for NSWGR and BR 5" gauge are drawn in 1 1/16" and our 7 1/4" are drawn in 1 17/32".