THE PROTOFOUR MANUAL	2.0.(1)
	SECTION 2. STANDARD DIMENSIONS.
	2. 0. PROTOFOUR_&_PREFERRED_PROTO-RATIOS.

When the Protofour 4mm/1ft scale standard track and wheel dimensions were finalised by the Model Railway Study Group in March 1966, many modellers in other scales expressed a desire to adopt the Protofour concept of authentic modelling. Investigation by the Group resulted in Proto-standards, and associated data, being computed for sixteen of the scales in common use throughout the world. With the exception of the basic Protofour 4mm/1ft, these scales fall into six groups, each centred upon a nominal track gauge and having variations of scale within each group according to country of origin. Since there were, even then, clear indications that the appeal of the Protofour concept was becoming an international one, a rationalisation of the basic scales was obviously necessary to avoid confusion.

Broadly speaking the situation was as follows. British scales are traditionally based on metric equivalents of imperial feet, with track gauges adopted from other countries. As a consequence these track gauges are generally out of scale. Whereas the American scales use inch fractions or decimal equivalents of feet with near scale track gauges, the European scales are expressed as round figure ratios, or proportions, of the prototype and have virtually correct scale track gauges. Furthermore the European series of scales is more evenly spaced, and achieves a near consistent (approximately twofold) area ratio for adjacent steps in the scale series.

In attempting to resolve the problem of rationalisation many factors were borne in mind; firstly, the obvious need to retain the Protofour 4mm/1ft scale as the British basis of the Protofour concept. Britain, Australia and New Zealand are joining 90% of the world’s population by adopting a metric system, while the United States and Canada are considering similar changes. In a generation or so imperial-based scales will not only be obsolete, but they will leave an illogical series of decimalised ratios peculiar to this country.

It seemed logical, therefore, to suggest the adoption of the European series of round figure ratios, as this also has the advantage of offering internationally accepted track gauge dimensions which are themselves virtually dead scale; the worst case of such rounding up error is only 0.35% in Proto-160. amounting to less than 0.032mm over gauge.

Six scales other than the basic Protofour 4mm/ift scale have been selected for adoption as basic scales and these are termed the Preferred Proto ratios. The accompanying table is headed with the basic Protofour standards, followed by the track and wheel dimensions, with tolerances as necessary, for the six preferred Proto ratios. For consistency these dimensions and tolerances are directly proportional to the Protofour dimensions. It is important to emphasise that although the preferred ratios give decimalised metric/imperial feet scales, the provision of conversion tables, charts and prototype information compiled by the Study Group completely eliminatesthe often quoted problem of metrication. One very important aspect of the preferred ratios is that it will be possible for modellers in other than 4mm/1ft scale to continue using their traditional track gauges, but with turnouts and wheels correctly scaled to the appropriate Proto-standard for improved appearance and performance.

Research and the development of products to the preferred ratios is continuing within the Study Group and the Protofour Society. Comments and enquiries on any aspect of the standards and their use will be welcomed, and should be addressed to the M.R.S.G., c/o The Editor of Precision, the Journal of the Protofour Society.

September 1970

STANDARD DIMENSIONS FOR PROTOFOUR

Scale 4mm to lft. (1:76.2)

	THE PROTOFOUR MANUAL	2.0.(1)

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