A New Approach to Modelling Standards by A Model Standards Study Group
J.S. Brook Smith
Dr. B. Weller
READERS of the MRN from April, 1962, onwards will recall the correspondence and articles on the subject of EEM Gauge, an experiment into the possibilities of authentic modelling in 4 mm/ft. scale. Results of the experiments were sufficiently convincing to warrant the development of a proper table of standards suitable for general use, and to this end a Model Standards Study Group was formed.
The Study Group undertook four projects:
1. The tabulation of the requirements of small scale railway modelling.
2. The choice of a suitable scale for modelling.
3. The development of a table of working dimensions.
4. The introduction of a programme of tooling for gauges andcomponents.
These projects have been brought to a successful conclusion in the form of "Protofour" - a new Table of Standards for authentic scale railway modelling.
Protofour has been so named because the standards were derived from the prototype and as such are the first fully integrated and justified standards for railway modelling in 4mm. scale. Protofour is a complete breakaway from past practice, and it supersedes the experimental EEM Gauge, which, having served its purpose, is now abandoned and the settings withdrawn.
Scale Railway Modelling requirements
The investigation into the problems of small scale railway operations developed into a most fascinating study, which produced results quite unexpected when the study began. The most important of these results was the discovery of defects in the BRMSB recommended Standard Dimensions. In BRMSB modelling there is no specification for the contour of the running rail head, and only a vague definition of the contour of the wheel tread and flange. Investigation shows that these two contours together, control the entire structure of track and wheel settings. In the prototype, wheel and rail contours are laid down in the British Standard Specifications, and regular shop checks ensure that wheel treads and flanges are within limits, or the wheels are re-turned or given new tyres.
Control of these fundamental dimensions is not practised in railway modelling, where manufacturers are free to produce wheels and rail to their own specifications of contour, without proper consultation with other manufacturers, and with no responsibility for the results. As a wheel showing only slightly different appearance to another may have very different running characteristics, reliability of running under the present BRMSB rules of play is something of a lottery.
Protofour has an advantage over BRMSB in that the wheel and rail contours have been taken from the prototype, and these form the basis of the remaining settings. A further advantage is the adoption of correctly proportioned flange depths. The flange depth controls to a large degree the width of the flange, and therefore, the flangeway width. As the width of the wheel cannot be less than twice the width of the crossing flangeway, it will be seen that the flange depth controls wheel width; deep flanges and scale wheel widths simply cannot co-exist, and a comparison of BRMSB and prototype flanges makes this point abundantly clear.
While discussing flangeways, it might be opportune to mention that prototype flangeways are not necessarily of equal value. The crossing flangeway is always set at 15/8", and this spacing is maintained permanently by bolting the rails together with spacing blocks, or by special chairs. However, with gauge widening on curves, and with the check rail set only in relation to the outer running rail, the flangeway between the check rail and the adjacent running rail is simply the difference between the Track Gauge and the Check Gauge at that particular point.
On prototype tracks the gauge is deliberately widened on curves, those less than 5½ chains radius having an increase of ¾in. to 4ft. 9¼ in. At the other extreme LTE straight track is normally gauged at 4ft. 83/8 in. and widened on curves to 4ft. 8½ in., but this is a special case where long inflexible wheelbases are not found. Both gauge widening and fixed and variable flangeways are a feature of Protofour operations.
The EEM experiments aimed at controlling running conditions by checks made with only two gauges; while this was perhaps too optimistic, it was nonetheless, very close to the truth. Completely reliable operations in any model railway system require the control of five dimensions :-
1. Both wheel and rail contours must be matching sets for the standards in use.
2. Wheel spacing on axle (BB) must be correct.
3. Track Gauge (TG) must not be less than the nominal value, and should include a gauge widening factor for curved track.
4. Check Gauge (CG) measured from the face of the check rail to the face of the outer running rail, must not be less than the nominal value.
5. Crossing Flangeway (CF) between the wing rails and the vee at a crossing, must be a specified value.
Once again it will be seen that the wheel and rail contours determine the remaining dimensions.
Although Protofour settings may be translated into other modelling scales, the choice of 4 mm/ft. scale was made to avoid confusion between established standards and also to take advantage of the many detailed superstructures and other equipment produced in this scale.
The table of working dimensions has been derived from prototype settings and represents what is believed to be the closest practicable approach to correct scale in 4mm. modelling. It will be seen that wheel and rail contours are specified, and that a new dimension "Effective Flange" is used in the calculation of wheel settings. Effective flange is the thickness of the flange measured between the gauge face of the rail and the back face of the wheel with the wheel deflected against the rail. This may be very different to the Nominal Flange, and in the case of the BRMSB wheel it is the effective flange that puts the standards into question. Having justified the Protofour standards by computer, there is no doubt on the part of the Study Group that they are entirely practicable.
|TG||TRACK GAUGE||4' 8½"||18.83||18.83||MIN|
|CG||CHECK GAUGE||4' 6¾"||18.25||18.15||MIN|
B.S.S. 9 EQUIV*
SEE DWG P4-1**
|BB||BACK TO BACK||4' 55/8"||17.87||17.67||MIN|
|BB+EF||CHECK CLEARANCE||4' 63/8"||18.25||18.15||MAX|
SCALE BULLHEAD RAIL CONFORMS.
|** P4-1 WHEEL MANDATORY|
The five dimensional checks mentioned earlier must be made by the modeller or incorporated into manufactured components. The wheel contour is obtained through the use of form tools made to close tolerances by specialist firms, and designed for production runs or the modification of suitable stock wheels.
Correct section rail is obtainable from the Model Railway (Mfg.) Co. Ltd. of Kings Cross. This has finally made authentic modelling possible in 4mm. scale, and is one of the most important developments in the British market in many years.
The provision of the correct rail and wheels leaves the modeller with four further checks to carry out; Track Gauge, Check Gauge, Crossing Flangeway and Wheel Back to Back. The track gauge includes gauge widening for curves.
To whatever gauge the modeller works, the correct rail and wheel, plus the four gauges, must form the basic equipment. With Protofour, these checks are at least clearly specified.
Copyright - Model Railway Study Group, reproduced with permission.