Page:Model Steam Locomotives by Greenly Henry.pdf/195

Model Steam Locomotives railways. A typicnil design is illustrated in Fig. 217. Its only merit is that it makes gland packing a little easier and less troublesome. All types of slide bars, single, two-bar and four-bar, are often modelled by employing round rods, the crossheads being drilled to suit them, after the manner shown in Fig. 218. The tubular slide bar may also be employed where the cylinders have cylindrical stuffing boxes and no other provision for fixing the bars. In such cases a separate socket is often made to hold the bars, and then, complete with the bars, pushed on to the cylindrical stuffing box as shown in Fig. 219. For small models Figs. 218 and 220 show two simple modifications of the orthodox pattern. In the first the crosshead is drilled for the slide bars, which are two rods projecting from the cylinder cover. The other is provided with a slotted slide bar. The holes for the crosshead, Fig. 218, need to be carefully jig-drilled to ensure align- ment with the tapped holes in the cylinder. Motion Plates.-The illustrations (Figs. 221 and 222) are typical of those employed for inside- and outside cylinder engines respectively. They, in all cases, need modification to suit the disposition and dimensions of the particular form of valve gear and motion adopted. In the normal engine with a leading bogie it will be found necessary to allow plenty of clearance for the bogie wheels and frames at the points marked a on the two drawings. The special pattern of outside bracket is necessiiry in some forms of six- and eight-coupled engines, and is sometimes made up of plate material as a pierced or “spectacle” plate. The forked pattern of bracket is perhaps the best, but in some cases the characteristics of the prototype require 186