This section will be about the electrical aspects of laying pointwork.

There is a section of the Manual about the design and construction of trackwork, it can be found here Track

The Original Manual also include very comprehensive sections on building and wiring trackwork for DC.Guild Manual

The switch blades can controlled from the edge of the baseboards by wires or rods laid over or under the baseboards and Figure 1 shows one way of achieving this with a slide switch and “wire in tube” fixed down to the baseboard surface.

Slide switches are available with various sizes including some that suit the throw of O Gauge points. “Wire in tube” systems are available from Wizard Models, MerControl and model aircraft suppliers. The latter also refer to them as “Bowden tubes” or “snakes”.

The ptfe tube and nickel silver wire system can be bent down to 50mm radius to accommodate points that are not parallel to the baseboard edge and angle cranks are also available for points in very hard to reach locations.

Where points are roughly parallel with the baseboard edge they can be controlled by almost any small diameter rod (dowelling, bicycle spokes, welding rod etc.) laid in grooves cut into the base board surface or passing through the supporting framework below. Over the years many articles about different ways to do this have been published in the modelling press and no further details will be included here.

There are three types of widely available point motors; solenoid, slow-acting (stall current) and servo. They are usually designed to be mounted below the baseboard with an operating rod passing up through the baseboard to move the switch blades back and forth.

For those of us not keen on crawling about under our model railways, all of these point motors are readily adapted to be mounted above the baseboard and to move the switch blades by wire-in tube, some manufacturers produce mountings to facilitate this. At 1:43 scale these motors are small enough to be disguised with small lineside structures.

Wireless Control

WifiTrax make a range of products to enable wireless control of a model railway. Their range includes a universal switch machine control for up to 8 solenoid or slow acting point motors.

To operate a point or signal then, three things are needed; a servo, a mounting and an electronic controller.

The generally recommended servos are the TowerPro SG90 and the HobbyKing HK900, these cost a few pounds and are widely available from model aircraft and robotics suppliers.

It is not difficult to scratch build a suitable servo mounting using aluminium angle or mdf and most suppliers of electronic servo controllers also supply suitable mounts in a variety of materials.

For the avoidance of doubt the first illustration describes the main components of a standard point and these are the terms used throughout.

Figure 2 shows the problems that can arise with points built with switch rails, closure rails and the crossing vee built as one electrical unit.

The short circuit caused by the back of a locomotive wheel touching the switch blade should be momentary if the locomotive is moving. On a DC system the locomotive might briefly hesitate and the overload warning light come on, without causing any permanent damage. DCC command stations, however, have sensitive electronic short circuit protection and the short is very likely to close the command station down necessitating a system reset.

Some ready made points such as Peco Electrofrog rely on the contact between the switch blade and running rail to power the frog assembly. It can be difficult to keep this narrow gap clean and point motors need very careful adjustment to make sure that there is enough contact pressure for electrical continuity.

With this power switching arrangement only the rails in the direction for which the point is set have the correct polarity. The non-set rails will have a potential dead short if (as is generally advised) each discrete track section is fed direct from the track power bus.

There are some simple remedies to these problems.

Figure 3 shows a point modified to work reliably on both DC and DCC systems. Electrically this is the same as a Peco Unifrog point.

The switch blades are insulated from the frog assembly and electrically bonded to their adjacent stock rails, this both eliminates the potential short if a locomotive wheel touches the switch blade and also ensures that the switch blade is reliably connected to the track power bus.

Most point motors have built in switches that can be used to change the polarity of the frog assembly according to which direction the point is set for, this is also more reliable than the contact between the switch blade and stock rail described above.

The frog rails are insulated from the on-going stock rails and the latter are connected direct to the track feed bus.

This arrangement is ideal for DCC systems as every track section of which a locomotive might travel is energised and to the correct polarity. This is a slight drawback for DC systems because it is not possible to isolate a track section to “park” a locomotive without the use of additional section isolation switches.

Figure 4 shows a point modified for DC systems. Power feeds to the stock rails that are connected to frog rails is taken from the switched feed to the frog assembly. Thus the track in the direction to which the point is not set is electrically dead.