I am modelling in 4mm to the foot in OO gauge and my railway is my relaxation and enjoyment. To quote Peter Snow: “OO gauge is a lovely sensible practical gauge” to which I would add: “it’s not too big and not too small”. I know all the arguments for and against OO, EM, P4, etc, and can’t get excited about the additional precision afforded by a proper 4'-8½" for a railway that will rarely be viewed close up. Converting to EM or P4 is not just a matter of moving the wheels out. EM and P4 include a complete set of finescale standards for wheels and turnout clearances and some sort of compensation to all of the rolling stock is necessary unless you are confident of achieving perfect track. I have accumulated enough OO stock to make a conversion quite extensive and expensive, conversion would be all-or-nothing, it is not possible to do this progressively and still run trains.
My interests lie in achieving a good representation overall and in operating the railway in accordance with my interpretation of prototype practice. I spent several years working overseas on railways with gauges varying from metre (Malaysia and Thailand) to 5'-6" (Pakistan and India) and lots in between, so I believe that “correct gauge” is a matter of perception. One thing I am doing is to lay my track with a nominally correct six-foot way. At 12" to the foot, the six-foot is measured between the outside edges of the rails so twice the rail-head width (2 @ 2¾") needs to be added to the 4'-8½" to give us a distance between track centres of 11'-2". This is 45mm at 4mm to the foot (to the nearest millimetre) and the corresponding ten-foot space, or wide way, for a four-track railway gives track centres of 15'-2" or 61mm (to the nearest millimetre). I say this is “nominally correct” because, of course, the six-foot dimension is as wide as the track gauge is narrow. However, the track centre-to-centre distance is correct and thus the passing clearance between trains is right. The track spacing for British OO gauge sectional track is now standardised at 67mm (2⁵/₈"). This was arrived at by the use of the geometry of a standard sectional curve in turnouts when forming a crossover and it allows for the extra width needed for the overthrow of bogie vehicles on the tighter curves. This extra clearance is unnecessary on straight track and where gentler curves can be used. Where curves tighter than about 3 foot radius are necessary, the spacing can be eased out without being too obvious.
Having set out my aspirations, I realise that I need to run some tests with trains passing at speed on some long straights to check how much dynamic movement (wobble) I will get. At 12 inches to the foot this would be understood as an assessment of the kinematic envelope. If this is too much, I may need to widen my six-foot somewhat, perhaps to 50mm, with a corresponding increase in the ten-foot way to, say, 65mm, to keep the proportions looking right. Indeed, 50mm seems to be the normal dimension adopted by some 4mm finer scale modellers.
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