wheels, flanges and back to backs

Wheels of railways are a great deal more complex than first meets the eye. The angles of the tread and the radius between the flange and the tread (blue area) are very carefully worked out to minimise friction and wear. Full size railways even use different materials for parts of the wheel profile. At regular intervals the wheels are built up again with weld and ground down to specification.

When model railways first began to become popular, no one cared very much about accurate rendition and concern was that the train stayed on the tracks. Wheel profiles could be described as 'agricultural'.

Many model railway manufacturers, have over the years developed their own standards and for a period of time, 00 scale trains could not properly run together. It was an excellent way to force customers to remain loyal to Hornby, Trix or Triang, I suppose. The problem was solved by Wren 'universal two or three rail track' by developing points that did not operate like the real thing at all.

Gradually, due to company takeovers, some standards became established in OO scale. Sadly, the scale included track was was a scale several inches too narrow. The Europeans from the start elected to build models in H0, which rendered the track gauge of 16.5mm correct. Nevertheless, they took a long time to standardise wheel, coupling and track standards. The whole sorry story of 00 is proof to me why Britain will always be a reluctant member of the EEC.

Things improved with the introduction of Peco track and even a chaired track system became available from Chairway.

Gradually, serious modellers in Britain have established more scale track gauges. EM gauge, (18mm gauge) and subsequently scales like protofour, (18.83mm). This is fine scale.

In these new scales, flange depths have been reduced to scale and for the first time in the UK, model 4mm/ft trains look right.

Most 4mm/ft modellers still use the 00 narrow gauge track and run their trains with deeper flanges than scale and heavier rail. This is course scale.

Similar differences exist between fine and course scales in gauge 0, 1 and upwards.

Points are now built as in prototype practice.  As the frog is fixed, outer check rails are needed to guide the wheels and prevent them hitting the point of the frog which will result in a derailment. The means that the gap between the stock rail and the check rail have to be specified and accurate. Likewise, the back to back measurements of the railway wheels have to be accurately set. Below are shown the dimensions for fine scale 00 gauge. Back to back measurements must be checked for all wheels. A gauge can be purchased for most scales.

Some commercial points, such as those of Peco, have the frog set in plastic so when a wheel cross the gap at the frog, the flange is supported. Sadly, wheels do not all have flanges set to a standard depth and some, such as Riverossi N scale, have such deep flanges that they will jump at the frog. It is then necessary to excavate the plastic to allow the wheel to cross freely (or throw the Riverossi away).

4mm two foot narrow gauge

Early narrow gauge  modellers had it all to do themselves. For those modelling 2ft gauge railways, a track gauge of 8mm was sensibly chosen. From the Hatfield, UK, came a company called Lone Star. They built die cast toys including things such as cap pistols. A range of push-along trains were released with a track gauge of 8mm. Eventually these were motorised and a new gauge of 9mm was selected. It was called 000 which was the start of the popular N scale.

These days, most of use who model in narrow gauge, employ the N scale gauge as standard although a few people do model in fine scale and 8mm gauge.

Models of three foot/metre gauge railways used TT scale track, (12mm gauge).

There is a standard for N gauge which is relatively fine scale. It was set by the NMRA (National Model Railroad Association).

Drawing from NMRA S-3.2 on track standards.

Norm/standard Gmin
NMRA S-3.2 8.97
7.92/8.05 *)

Drawing from NMRA S-4 on wheel standards.

Norm/standard -
NMRA S-4.2, RP25 -
0.56 **)

Drawing from NMRA RP25 on wheel profile.

Norm/standard N' T W D' P R1 R2 R3
NMRA RP25 1.83 0.51 1.32 0.51 0.18 0.20 0.23 0.23

Rather sadly, this standard did not really travel well to Europe and there is still a ghastly profusion of course wheel standards out there. So those working in H0e and 009 are left with having to fiddle around with our pointwork to find some happy compromise, unless we are absolutely brutal and insist on one wheel standard. Sadly, this is not always possible for those of use who have large collections of stock. Peco track seems to have found some reasonable compromise although the crazy track points should be avoided at all costs.

early Minitrix pizza cutter flanges