What is point rodding in model railways?

Point rodding is a system of rods and bars that physically joins the lever of a signal box or ground frame with a set of points. They were a feature of manual signal boxes during the days of steam and could be seen running alongside railway tracks between the signal box and any points which came under its control. Although many have now been replaced with modern technology, a few have survived on the network well into the 21st century.

The concept of point rodding is quite simple - the signalman pulls a lever in the signal box, which in turn pulls on a rod that is connected to some point blades resulting in them moving into position.

There are two types of point rodding, one made from steel tubes and another made in the shape of a channel with a cross-section resembling an upside-down U.

Point rodding is supported just off the ground by special rollers that allow free movement of the rods whilst being operated, the supports are generally place every 6-8 feet along the length of the rodding but it should be noted distances between supports can vary to accommodate local requirements.

Another feature of rodding is called a crank which is a type of hinged joint. There are two types of crank used in a rodding's assembly, the first is called a bell crank and is used to facilitate a change in the rodding's direction allowing it to be routed to reach points, the second type is called a compensating crank and is used to break up long sections of rodding into independent smaller section, this is necessary to ensure that heat from the sun doesn't expand the metal of any single continuous section and move the point blades unintentionally. The clever design of a compensating crank acts as a pivot between two sections of rodding meaning that when one section is pulling, the next section is pushing, so any expansion is cancelled out in equal measures.