4mm scale chassis and underframes for our kits

This document briefly describes various methods of completing the underrame for our kits with suggestions and examples.

Bogie Stock

Our kits are provided with locating holes which allow bogies to be positioned at the correct centres. The bogie type and underframe detail depends on the company. For GNR coaches, the bogie type was usually a Fox's patent type, used by many pre-grouping railways.  Later, LNER standard (Gresley) bogies would have replaced the Fox's bogies. Fox's pattern bogies had coil springs either side of  a central cross member.  An image of these bogies can be seen below in the section on articulation.  A number of pre-grouping lines used this patent bogie. Some BR bogies were quite similar to Fox's bogies in external appearance and can be adapted to suit by the modeller. There are detailed drawings of GNR 45' stock in "Historic Carriage Drawings" by N. Campling pp. 94-95, ISBN 1 899816 04 6.

Six wheeled Stock

There are a number of ways of making an underframe for a six wheeled coach.  The choice of method depends on the track. Sharp curves cannot be negotiated by a rigid six wheeled vehicle. The minimum allowable radius of the curves depends on the gauge of the track and the available freedom of movement of the axles.  The first image below, taken from “The Engineer”, 1878 shows how a six wheeled carriage is constrained by the track. The second image shows a Cleminson truck. The outer axles are pivoted. The movement of the outer axles is then transmitted to a floating central axis using a mechanical linkage.





In general, a four foot radius curve in “OO” can be negotiated by short six wheel coaches with prototypical lengths up to about 32 feet.  This minimum radius is increased for “EM” and “P4” (A wider gauge reqiures larger radius curves).  A simple modelling solution is to reduce, or eliminate, the flanges on the centre wheels. A basic alternative is to make the central axle pivot with side and vertical play.  A "T" arrangement using a tube soldered onto a thin springy wire works well (the sort of thing that Rev. P. Denny was making years ago). The third image shows a similar concept, painted black, constructed from wood. The central axle has sideplay and some rotation. This vehicle (a GNR 281 third break) will negotiate 3ft curves in “OO” gauge.

There is a discussion thread about Cleminson trucks on Rmweb at .

Another discussion thread describes the manufacture of a 6 wheel chassis for our D281 brake kit.

These threads mention a number of suppliers of etched brass kits. It is also possible to make Cleminson trucks using a 3d printer.

Articulated sets

Articulation of rolling stock is not a new idea. The engraving below was published in 1869. The photograph was published in 1913

Many six wheeled coaches were made into sets using bogies by N. Gresley for the GNR and LNER. This arrangement is fairly easy to model, using Fox's pattern bogies for GNR. Later, LNER standard bogies would have replaced the Fox's bogies. Fox's patent bogies had coil springs either side of a central cross member. A number of pre-grouping lines used this patent bogie. An example bogie with a 7ft  wheelbase taken from a SE&CR coach drawing is illustrated. GN/LNER bogies were 8ft or 8ft 6in wheelbase, Some BR bogies were quite similar in external appearance and can also be adapted to suit by the modeller.

“RMweb” thread on Diagram3D coach construction

Diagram3D coach construction was covered in a discussion thread on RMweb. The link to this thread is

Small Parts and availability

Small parts are available from a number of speciality manufacturers. Diagram3D does not maintain stocks of 3rd party products or make recommendations on the suitability of these parts.