EM Gauge
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EM gauge (named after the track gauge of a nominal Eighteen Millimetres) is a variant of 4 mm to a foot (1:76) scale used in
model railway Railway modelling (UK, Australia, New Zealand, and Ireland) or model railroading (US and Canada) is a hobby in which rail transport systems are Model building, modelled at a reduced Scale (ratio), scale. The scale models include locomotives ...
s. EM was developed because
OO gauge OO gauge or OO scale (also, 00 gauge and 00 scale) is the most popular standard gauge model railway standard in the United Kingdom, outside of which it is virtually unknown. OO gauge is one of several 4 mm-scale standards (4 mm to , or 1: ...
, favoured by manufacturers of British prototype models, utilised track that was too narrow. OO was developed in the UK in the 1930s as a response to manufacturers finding they were unable to fit the motors of the time into British prototype small boilered locomotives when scaled at the globally popular
HO scale HO or H0 is a rail transport modelling scale using a 1:87 scale (3.5 mm to 1 foot). It is the most popular scale of model railway in the world. The rails are spaced apart for modelling standard gauge tracks and trains in HO. The ...
's 3.5 mm to a foot (1:87). As the scale was increased to 4 mm to the foot to make the locomotives larger, the track gauge was left at , and hence is too narrow (by a scale ) to correctly depict the prototype's
track gauge In rail transport, track gauge is the distance between the two rails of a railway track. All vehicles on a rail network must have Wheelset (rail transport), wheelsets that are compatible with the track gauge. Since many different track gauges ...
of . EM gauge was founded in the 1950s, originally with gauge track and
rolling stock The term rolling stock in the rail transport industry refers to railway vehicles, including both powered and unpowered vehicles: for example, locomotives, Railroad car#Freight cars, freight and Passenger railroad car, passenger cars (or coaches) ...
wheelsets based upon the crude and massively out-of-scale products of the contemporary OO model manufacturers. 18 mm gauge was still undersize by almost a millimetre. With the limitations of modelling at this time, particularly the width of tyres, the largest gauge that could fit within the outline of a scale model would be 18.5 mm, no larger. This was mostly an issue for steam locomotives, where the popular technique at the time of making connecting and coupling rods from rail required an excessive spacing between wheel faces and the cylinders. Attempts to make finer tyre and flange standards were thwarted initially by the overscale rail sections available commercially, it being impractical for an individual modeller to make smaller rails – although some did attempt to, by cutting down commercial rail. Smaller flange and tyre dimensions were also unsuccessful, as the narrow tyres tended to detach from the wheel centres. More critically, small flanges required comparably smaller rail, trackwork gaps and point frogs in order to work reliably. Wheelset standards did become more fine in time, allowing EM to evolve into gauge track (for a while called EEM gauge until it was adopted into the mainstream standard). Some modellers were still not happy with this, it is still a scale too narrow, and developed the P4 standards ( gauge). Most EM modellers will have started off using OO gauge and having acquired the necessary modelling skills, then advanced into EM. Modellers in EM typically re-wheel their rolling stock and hand-build their trackwork, although pre-built track is available from specialist suppliers. There are also many 4 mm scale kits which can be used by all 4 mm scale gauges, and since the advanced skills, advanced kitbuilding and scratchbuilding are also common. EM standards are set by the EM Gauge Society, defining gauge and wheel dimensions to ensure compatibility across layouts.


See also

* Pendon Museum *
Rail transport modelling scales Rail transport modelling uses a variety of scales (ratio between the real world and the model) to ensure scale models look correct when placed next to each other. Model railway scales are standardized worldwide by many organizations and hobbyi ...


References

{{Reflist, refs= {{Cite book , title=The 4mm Engine , last=Williams , first=R. Guy , author-link=R. Guy Williams , year=1988 , publisher=Wild Swan Publications , isbn=0-906867-70-3 , page=1


External links


EM Gauge Society
4 mm scale