Model Railway News
A New Approach to Modelling Standards by A Model Standards Study Group
J.S. Brook Smith
Dr. B. Weller
Concluded from Part 1/2: Model Railway News, August 1966
It is clear from the Study Group's investigations that the BRMSB standards lack the basic dimensions to ensure complete reliability, i.e., standard wheel and rail contours designed to work together. Secondly the BRMSB dimensions can be shown to be critical in certain situations, and in the case of TT3, clearly defective. Under these circumstances, the Model Engineering Trade Association's task is indeed a thankless one.
The Protofour Standards, by adopting prototype practice, have eliminated these basic weaknesses and at the same time offer a balanced structure of dimensions and a truly prototypical appearance in the finished model.
For those who have no interest in accurate representation of the prototype, the BRMSB systems offer a range of components with which a working model may be assembled. On the other hand, those who are prepared to adopt minimal springing in the vehicles and to attempt to lay reasonably level track, can now produce a reliable and correctly scaled model railway with a completely authentic appearance.
With BB spacing plus twice the tyre width, it can be seen that the clearances between axleguards are almost the same as EM Gauge. This feature, combined with gauge widening, means that there are no greater restrictions on minimum radius curves than in the present EM Gauge.
The many technical advances on the present systems, and the correct appearance of the models, give reason to believe that Protofour might become the accepted scale railway modelling standard of the future.
In the diagram, four model wheel contours are compared to each other, and to a British Railways wheel drawn to the same comparative scale.
The diagram shows the variations in flange contours between model wheels in the same general category, and the variation in wheel clearances between standards.
The wheels are shown with a common datum, i.e., the wheel back. It is assumed that in all cases the opposite wheel back is in contact with the check rail; the running rails are thus positioned in accordance with the published standards. As the BRMSB wheel has an effective flange greater than the nominal figure, (approximately 0.8 mm. versus 0.5 mm.) the interference at the nose of the crossing can be seen as a shaded area.
A curiosity of the BRMSB standards for "00" Gauge is the discrepancy between the published check gauge and the distance over checks + flangeway, which should be identical, but in fact differ by 0.25 mm.
Unrestricted. Tyre width 2.00mm., minimum.
Possible interference at the crossing nose. Tyre width 2.00mm minimum.
With stated check gauge of 15.30mm., similar interference to EM Gauge. With check gauge 15.25mm. (distance over checks + one flangeway) operation satisfactory. Tyre width 2.50mm., minimum.
Unrestricted. Tyre width 2.70mm., minimum.
May be used if wheels are set to H0 BB gauge of 14.4mm. and track check gauge is standardised at 15.25mm. See (3) above. Tyre width 2.50mm., minimum.
Unsatisfactory owing to excessive flange width.
Copyright - Model Railway Study Group, reproduced with permission.