Great Western Echo — No.89. Spring 1985 pp.7-11
‘The Didcot Signals’ by Alan Price
© Great Western Society
Obviously the centre piece of any display of signalling is bound to be the signals themselves and the ones we have constructed already at Didcot have been the result of an enormous amount of thought.
In choosing what signals we wanted we often found ourselves with a dilemma. We must have signals that are photogenic and easily seen but signals that are too large will not be aesthetically acceptable on such a small scale site. We want to preserve obviously as wide a cross section of signalling as we can but clearly too many signals would be ridiculous and unnecessary. To reconcile these problems we have stuck rigidly to our basic project guideline - is it how the G.W.R. would have done the job?
The Radstock end of the site is now complete with all its signals and has been supplied with a set to fit the period around 1925 which is when distant signals went from red to yellow and when the first use of metal arms began. This then represents a significant period in the development of G.W. signalling. No. 2 signal on the link line is a standard wooden 3' arm with loop. This was put on the signals to indicate its application to goods lines or loops in places where confusion could exist. The 3' arm is normal for goods lines not usually meant for passenger running. It is constructed on a concrete post which came from Filton Junc. in 1976. These posts were made at Taunton Concrete Works from about 1917 onwards under licence from the M. & G.N.Jt. who held the patent. They were brought in as a cheap replacement for timber which was getting scarce at the time and over 100 were erected between 1918 and 1928, many in S. Wales. Ours is rather unusual in that it has no oval holes which were put in to reduce weight and give a handling point on what were very heavy objects. The post is drilled at standard positions to take the fittings - a range of options being catered for. The finial is also unusual in that it only has two sides to the base. This was because the concrete could not be trimmed to provide a snug fitting as was the custom with timber and so it was bolted tight to one face instead.
Signals 3 & 5 are on a normally proportioned bracket for a left hand turnout. It is deliberately small to suit the scale of the location and is constructed on a main post from Upton Lovell's down distant (Sic. Whilst the signal was originally constructed as a single post using the post from Upton Lovell, when it was reconfigured as a bracket, it is thought that the post, bracket and doll from Congresbury were used and the Upton Lovell post used elsewhere (thought to be Signal R.20)). The doll (small subsidiary post) came from Congresbury along with the bracket itself. The 2' siding arm has a spectacle plate weighted with lead to ensure its return to the normal position. The green (blue) aspect is elongated to ensure that such a small lens lines up with the lamp over an arc of 40 degrees in the off position thus saving extremely fine adjustment of the fall. The red aspect, of course always lines-up exactly with the lamp because the arm rests on a stop in the danger position. The arm came from Gara Bridge. The main arm is a ribbed metal type dating from the period 1927-1945. There are obvious advantages in using metal for arms as opposed to wood and with an enamel facing they require no maintenance at all. The first metal arms had these ribs to strengthen them while later the edges were simply folded back to a right angle thus achieving the same effect for less manufacturing cost. These arms are still common on B.R. today. Ribbed metal arms were used with wooden spectacle castings but around 1927 a new spectacle design was introduced for use with metal arms and this signal is supplied with one of these. It was quite common for these arms to be found on wooden post signals, the implication being that it was a later replacement for a rotten wooden arm. Standard wooden post finials are used on both posts.
No. 16, 17 & 19 bracket is by far the most complicated signal we have constructed so far and has three arms on it. The main arm is a 4' ribbed metal arm married to a wooden arm type spectacle plate - again a common configuration. The post is a 25' (above ground level) piece of douglas fir and came from Radstock where it was the down home. The height is branded into the wood near the base (Note: The post has subsequently been replaced with new timber). The 7' below ground level is 14" square and this tapers from the 12' shoulder down to 6" square at the top. The bracket section and the doll came from Totnes. On the doll is a 3' main to loop or goods line signal. These signals only have loops on them when they actually referred to a movement on a loop or goods line but when, as in this case, they referred to a movement on a main running line to a goods line, the loop was omitted. The spectacle plate is a piece of sheet steel from the bonnet of a Wolseley. On the main post is a 1'6" calling-on arm. These were used to allow a train to enter a section that was occupied or obstructed. They were mainly seen at stations where they particularly were used to allow a shunting loco into an occupied platform to add or remove vehicles. The use of the full arm here would be inappropriate since it implies clear line ahead and could cause an accident. The letters ‘CO’ on the arm signify the function. Shunt and Warning signals were very similar with subtle distinctions in the Rule Book separating their use or which was used where. Prior to World War 1 Shunt signals had a large ‘S’ on them and were 3' arms. Sometime around 1940, the calling-on arms changed to red and white horizontal bands which can still be seen in numerous locations today. The lamp behind the arm has a sideways periscope arrangement of mirrors so the light is cast onto a large translucent screen bearing the letter ‘C’.
No. 20 signal is a standard wooden post from Congresbury (Sic. Actually now though to be the post originally from Upton Lovell) with a normal wooden arm and standard spectacle plate casting. The spectacles on these were very large and it illustrates well the use of blue glass for the clear aspect, which of course goes green with a yellow lamp flame. The signal is fitted with a sighting board. These were used to provide a white background for the arm in places where the background was confusing or dark. In this case it is apt since the larger bracket signal further up the line can cause sighting confusion.
Signal No. 8 controls the exit from the siding which is protected with trap points. It is a disc signal of the 1918 period, one of the first generation of true disc signals used in sidings and goods yards for short local movements associated with shunting. The face is 12" in diameter (Sic. The disc is actually 16 inches in diameter), with a rib around the edge. It is made of vitreous enamel on sheet steel like the metal signal arms. As time went on later designs of disc signal were shorter and the faces tended to be smaller but these signals are in my opinion truly elegant examples of their type, standing some 3 feet high. The actuating arm has a rod connected to it which locates in a hole in the blade connected to the blade of the trap point. This is a simple method of detecting that the blade has moved exactly as it should. If there is the slightest gap the signal will not clear.
In addition to the broad gauge period disc and crossbar signal erected by the Taunton Group we plan over the next year to erect two more signals both at the Transfer Shed end of the site. The first is a double arm slotted post signal on the mixed gauge side of the period 1870 and the second is a short right-hand bracket using our converter bracket casting. This latter signal will have a main arm and a calling-on arm on the main post and a centre balance arm for the deviating route with a 3' wooden arm. We are also planning to erect a fixed distant on an extended No. 8 road since we have no distants on the site. The only notable designs of signals that will not be represented therefore in our display will be the working distant signal and the unique G.W.R. backing signal.
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