Nikola Tesla Books
106 HIGH FREQUENCY APPARATUS in the chuck and threading to the required length before cutting off. As shown in the detailed drawing, Fig. 3, the length of this spindle is 21 in. The frame plates 5 and 6 are iron castings. The pattern is a simple one that may well be cut out on a scroll saw, the boss for spindle and the small elevation in each corner being turned separately and fastened on with brads and glue. The finished size of this casting is shown in Fig. 2. The one pattern serves for both castings, but the machine work on each casting differs slightly from that on the other. As will be noted, the central hole in casting 6 is tapped for the -18 spindle, while that on casting 5 is drilled and reamed to provide a good sliding fit for the plain portion of the spindle 3. The clearance holes for the pins in the upper electrode casting are also indicated in casting 5. A smooth file-cut on the corner bosses finishes the machine work on the frames after all holes have been drilled. The four corner posts are of fiber rod 3/4 in. in diameter and faced off accurately to 4½ in. in length. Tapped holes are made in the ends for the 1/4-20 screws which fasten the structure together. The remaining details are obvious in construction. In assembling the gap, the feet and four corner posts are first secured to the lower frame. Then the lower electrode is set up tightly on its spindle in the frame. The upper electrode is placed on the lower and the coiled spring slipped over the spindle. The top frame is next slipped on, making sure that the pins engage the proper holes in the frame. The driving home of the corner screws and screwing on of the insulated adjusting knob completes the assembly, and the builder is ready to see how well he has done his work. The only "snag" is likely to be found in the inaccuracy of the filed bosses on the upper frame. To make a thoroughly good job these should have been faced off in a lathe at the same time as
