The ordinary track-spikes are very largely responsible for the removal of ties, since they induce decay around the spike-hole even if the tie is not spike-killed by the frequent re-driving of spikes. Even the treated ties are ruined by the spikes, especially when the ties have been treated with a chemical which is soluble in water, since the water will soak into the spike-hole and leach the chemical, which then leaves the wood-fibers unprotected and subject to decay. The best substitute for spikes, and the method which has been frequently adopted, is the screw-spike. Although the details of their design as adopted by various roads have a considerable variation, they all agree essentially in having a length of about five or six inches; have a square or hexagonal head so that they can be screwed with a suitable wrench; they taper to a blunt point, and have a screw-thread similar to those used for any wooden screw. Of course one essential to the form of the head is that it shall have a flange wide enough to extend over the base of the rail and thus hold it down. It is essential that a hole, somewhat smaller than the diameter of the spike, shall be previously drilled into the tie. When a large number of screw-spikes are to be placed, the work is accomplished by a drilling-machine, which not only does the work more accurately but with greater speed. It has been found by actual test that such machines can put in two screw-spikes while three ordinary spikes are being driven. Even the additional time required is much more than saved by the reduction in track-work made possible by the use of screw-spikes. Although the holding-power of screw-spikes, compared with ordinary spikes, varies with the character of the wood, the average of a large number of tests showed that the relative holding-power of screw-spikes and common spikes in white oak was as 1.87 : 1, while in long-leaf pine the ratio was as 4.63 :1. This shows that screw-spikes are especially advantageous in soft-wood ties, which are so readily subject to spike-killing.

Fig. 21. Screw-spike.

112. Use Of Dowels

Another device for retarding the destruction of ties is the invention of a French engineer and consists in using a creosoted piece of wood, into which the spike, which may be either a common spike or a screw-spike, is inserted. A cylindrical hole is first bored into the tie; following this a shaper cuts a screw-thread in the sides of the hole already bored; the wooden dowels, which are already provided with a corresponding screw-thread, are then screwed in the tie. Since the upper part of the dowel is conical, the dowel is readily screwed down until it fits the hole, and there is no danger that water will soak in around the dowel. After the dowel is in place, another machine cuts it off even with the top of the tie. The dowel has a hole through the center which is bored the proper size for the insertion of the screw-spike.

Wooden dowels for ties.

Fig. 22. Wooden dowels for ties.

Usually a hole the proper size is provided, even when com-mon spikes are to be used. It is found that the comparative resistance to displacement, both lateral and vertical, when dowels are used with soft-wood ties is very remarkable, as it very largely increases the holding-power of the spikes and thus retards one of the most common causes of tie deterioration.