| Jens Emmerman, Henk Oversloot | updated 21/3/2000 |
Track standard:
standard gauge G = 9.0 mm gauge widening max = .3 mm *) flange clearing F = 0.5 mm between flangeways S = max 8 mm check gauge C = min 8.5mm minimum height H = min 0.5 mm
*) N.B. maximum gauge widening is based upon NEM 310 in order to be able to exchange scenic track modules between various group standards, for prototype scale wheels G max = 9,2 mm and recommended is to use an effective maximum of .1 mm for new modules. When using the Fremo advised 1 m minimum radius, gauge widening is not necessary.
wheel standard:
back to back B = 8.2 mm back over flange K = max 8.5 mm tyre width N = min 1.3 mm *) flange width T = 0.3 mm flange depth D = max 0.5mm
*) prototype tyre width of .9 mm will not run faultless over turnout crossings but does not lead to derailments.
Important details
The minimum gauge (9.0 mm) - 2x the flange width (2 x 0.3) mm
- the back to back (8.2 mm) = track tolerance (0.2 mm = 2 x 0.1
mm)
This dimension is also the maximum acceptable tolerance from
ideal dimensions due to manufacturing and mounting practicalities
-> back to back B + 2x tyre width T < 9mm (wheelset
should run free over rails)
-> back to back B > 8 mm = S between checkrails (back to
back the wheelset should run free through flangeways)
-> back to back B + flange width T < 8.5 mm = K (back to
opposite flange the wheelset should run free through crossings)
The wheelset should be running free in ALL positions (wheel
wobble + dimensional errors around circumference)
Test criterium is the clear running
through dimensional correct and error free pointwork
(to define all dimensions and clearances with exact tolerances will lead to dimensions that can not be manufactured and measured with the normal hobby equipment of the average modeller. This extreme accuracy is not necessary as the above maximum tolerance of 0.2 mm shows. The above dimensions have been eased to make modelling more practical and are based on the 40 years engineering practice of the 2 mm Scale Association.)
The flange depth bears a relation to wheelbase and chassis construction. Chassis with fixed axles and long wheelbases profit from the maximum flange depth in order to compensate for track failures such as uneven track.Short wheelbase chassis and equalised or compensated chassis that guarantee track-wheel contact under all track circumstances may use wheelsets that are close to prototypical dimensions. Different flange depths may come to use within a single chassis depending on the application. Particularly the very visable pony and bogey wheelsets can often profit from finer flange depths due their independent suspension from the main chassis.
The nominal tread width is 1.0 mm but in practice this can be between the width of a standard N wheel(1.6 mm) and the minimal dimension of 0.8 mm without the wheelset falling in between the rails due to gauge widening.When one adheres to implementing a gauge widening of less then 0.2 mm throughout, smaller tread widths are possible, if a small dipping of the wheels into crossing gaps is accepted.
About 0.2 mm is used in the tapered section to the tread. This is also the range necessary for tolerances in track lineout (transverse offset) between modules and in the range of tongues in pointwork.Narrower flanges are possible (min. about .2 mm), but the track keeping properties due to dimensional track failures will be low. The wheelset will show a strong tendency to climb over obstacles when the track is not free of dimensional errors.
The actual flange tyre radius and conus are not very critical to collected experience. Particularly the surface flatness of the tapered section is important and the width of the tapered section should have a ratio of about 2/3 of the total flange width. The flange-tyre radius should not be too large. The ideal track play is circa 0.1 mm. With a flange-tyre radius larger than 0.15 mm the wheelset will be running on the radiused section and this will lead to a continuous rocking of the chassis along its main axis. Particularly "Fleischmann" wheels have a very large radius between flange and thread. When you use these as semimanufactured product than this radius should be machined. When the transition looks as an obtuse angle it is about right.