Nikola Tesla Books
168 HIGH FREQUENCY APPARATUS With the third coat of shellac quite dry, the cylinder may be mounted in the lathe between centers, a slender screw driven into the wooden head and catching a slot in the faceplate to afford a means of driving. The lathe should then be speeded up and the surface of the cylinder carefully gone over with the finest sandpaper to remove the inevitable irregularities caused by particles of dust and dirt. On no account must emery paper or cloth be used and the lathe bed must be scrupulously clean while the cylinder is being handled, as the least trace of metal chip or dust under the winding would be fatal to good results. The surface of the cylinder having been carefully smoothed over, the lathe may be prepared for the winding. The gears are set to cut 24 threads per inch and the winding of No. 30 D. C. C. wire is started one-fourth inch from the end. In starting, the wire should be passed through a small hole in the cylinder and the hole immediately plugged with a bit of wood covered with wet shellac. This will prevent the winding from coming loose during subsequent handling. The lathe should be turned slowly and backward, and the wire fed through a guide held in the tool post. When the finishing turn, the 300th, is in place, the final end of wire may be passed through the cylinder and secured as was the starting end. While the coil is still in the lathe, the winding should be coated with shellac applied in a thick solution and with a soft brush, the greatest of care being taken to see that the fluid soaks well into the turns and between them and also that no air bubbles or particles of dirt are permitted to remain. When the first coat has dried for an hour or more, the cylinder may be carefully removed and placed in the oven, wherein the temperature should not be over 150 degrees F. The baking may continue for a few hours and the second coat applied after the coil has been put
