It is well to fit the screw D' loosely, so that the flange f will come perfectly flat with the upper surface of the base plate B. The slide G N on the pillar D can be made of two pieces of small brass tube, one fitting the pillar D and the other the bar F. The slide G N is held in position by the set screw g, and the rod F by the set screw h.
The piece H can be permanently attached to the rod F. We show separate at Figs. 113 and 114 the slide G N on an enlarged scale from Fig. 109. Fig. 114 is a view of Fig. 113 seen in the direction of the arrow e. All joints and movable parts should work free, in order that the center I may be readily and accurately set. The parts H F are shown separate and enlarged at Figs. 115 and 116. The piece H can be made of thick sheet brass securely attached to F in such a way as to bring the V-shaped groove at right angles to the axis of the rod F. It is well to make the rod F about 1/8" in diameter, while the sliding center I need not be more than 1/16" in diameter. The cone point n should be hardened to a spring temper and turned to a true cone in an accurately running wire chuck.
The hollow cone end m of I should also be hardened, but this is best done after the hollow cone is turned in. The hardening of both ends should only be at the tips. The sliding center I can be held in the V-shaped groove by two light friction springs, as indicated at the dotted lines s s, Fig. 115, or a flat plate of No. 24 or 25 sheet brass of the size of H can be employed, as shown at Figs. 116 and 117, where o represents the plate of No. 24 brass, p p the small screws attaching the plate o to H, and k a clamping screw to fasten I in position. It will be found that the two light springs s s, Fig. 115 will be the most satisfactory. The wire legs, shown at L, will aid in making the device set steady. The pillar E is provided with the same slides and other parts as described and illustrated as attached to D. The position of the pillars D and E are indicated at Fig. 110.
