Engineering Wonders of the World
Volume I

228 ENGINEERING WONDERS OF THE WORLD. Fig. 6.—SAXBY AND FARMER’S FACING POINT LOCK. These possibilities have been negatived by the simple but ingenious Saxby and Farmer facing point lock, which is shown in Fig. 6, and is worthy of examination. A Point The points are shifted by one set of rods, B, and locked or unlocked by a quite separate set, H. Near the nose of the points is a stretcher bar, C, divided into two parts, one of which is at- tached to each switch. These parts are flattened out and overlap one another for about eighteen inches at the centre of the track. The overlapping portions ar© pierced with, two sets of holes, which under normal conditions coincide exactly. Should the bars connecting the switches break, the stretcher would divide, and the holes of the parts coincide no longer. Attached to the sleeper under the stretcher is a collar, through which works a plunger bolt, D, fitting the holes in the stretcher. This bolt is connected by rods and a rocking lever to a locking bar, E. The bar rides on swinging clips, F, and can be moved in either direction by the train of levers, HH, its upper surface rising at half-stroke to the level of the top of the rails. (The motions of the bar may be compared to that of one element of a pair of parallel rules.) If a vehicle happens to be passing, the bar cannot be thrown over, owing to the obstruc- tion caused by the wheel flanges, and conse- quently the bolt cannot be withdrawn from the stretcher bar, which, fact in turn prevents the shifting of the points. In the illustration the bar is seen lying over to the right, and the bolt withdrawn ready for the points to be shifted. As soon as they have been moved, the bar will be thrown to the left, and the locking bolt shot. It should be added that, should either of the tongues, AA, or the rods, KK, break, the two parts of the stretcher bar would separate, and the signalman would know, from his inability to shoot D home, that something was amiss. Interlocking. But these great improvements must appear small when compared with the introduction of the interlocking of points and signals. By this the lowering of conflicting signals— that is, those for opposing movements, such as signals 6 and 7 in Fig. 7—is rendered