[Fig. 51] is another, a little more ornate and of a different pattern. The process is essentially the same, except that there are no spurs and a solid disk is left inside. This disk is turned out of a ball, left inside the exterior shell. One side of it is squared up before the ball is cut free from the globe, and the job is then reversed and the other side squared. The ball is then cut free, and the loose disk is held fast between a flat-ended driver in the live spindle, and a loose, flat-ended button on the back center. The diameter is then decided through the hole which is toward the reader.
Fig. 52.
A little tool, which is very convenient for making small screws, is here shown in [Fig. 52], rather out of place, but it was overlooked before. In construction it explains itself. Holes of different sizes are made in a steel rod, and the end filed into shape, as seen. It has been found difficult by some to make these cutters work, but that was because they were not properly made. The trouble lies in drilling the hole. When the drill starts at first, the hole is larger on the outside, so that the screw blank, when cut, gets tighter as it goes in, and twists it off.
The remedy is, to drill the hole in some distance and then turn off the outside end, so that it gets where the bore is the same size. This refers only to small bolts, a sixteenth of an inch in diameter; where they are large, the trouble mentioned is not experienced.
It is convenient to have two sizes in the tool so that the heaviest part of the work can be done by one cutter, the tool reversed by turning it over in the fork of the jaws, and finishing the blank with the last cutter. A watchmaker’s fine saw is to be used to sever the screw from the rod. The tool itself is to fit in the spindle of the tail stock, and the screw wire is held by a drill chuck.
In the matter of ornamental work, there are other details and plans in vogue among experienced turners, which can only be alluded to, not discussed at length, for the reason that the styles are so numerous that an elaborate work might be made of them alone, with great profit. The scroll chuck or geometrical chuck, as it is sometimes called, is a complicated piece of mechanism, too costly for general use, and too limited in its application, to mechanics in general, to be of much utility. It does such work as may be seen on bank bills. The chuck plate, on which the work is fixed, is connected, by a train of gearing on its back, with a fixed gear about the spindle on the head stock, so that when the relation these gears bear to one another is altered, the motion of the work on the chuck is accelerated or retarded, or is made to assume certain positions. An elliptic chuck is quite another thing, the work done by it is shown in [Fig. 53], which consists, chiefly, of ornamental designs disposed in a certain order. In fact, the changes that can be made are infinite.
Fig. 53.
Mandrels—arbors, as many call them—are very useful tools. Mandrels are made of wood and steel—usually steel, and never of wood, unless for some special reason. As, for instance, when a large brass ring has to be turned. For this use a wooden mandrel is cheaper and more quickly made than a steel one. Besides, it is quite as good. Wooden mandrels should have iron center plates let in them, so that they will run true; if the center was made in the wood itself, it would be liable to run out. Take a piece of sheet iron, one eighth of an inch thick and one inch square, hammer the corners thin, then turn them over at right angles with the plate. This gives four sharp corners, so that, when driven in the end of a block, it will not slip; three small screws will hold the plate to the mandrel so that it cannot get loose. The center must then be countersunk, as any other is. Such a mandrel, made of hard wood, hickory for instance, will last a long time.