“During the early stages of the turning, or, in other words, during the roughing out, we must occasionally stop the lathe and examine the flat places on the body; for unless these places disappear evenly, the work is not true, and one half will be thicker than the other, so that the joint of the pattern will not be in the middle. It was to insure this that the pieces were directed to be planed of equal thickness, since, if such is the case, and the flat sides disappear equally and simultaneously during the turning, the joint or parting of the pattern is sure to be central. If the lathe centres are not exactly true in the joint of the two pieces, they may be made so by tapping the work on the side having the narrowest flat place, the process being continued and the work being trued with the turning tool at each trial until the flat places become equal. By this means, we insure, without much trouble, two exact halves in the pattern, which is very important in a globe valve pattern on account of the branch and other parts, not to mention the moulding. Having turned the body of the pattern to the requisite outline, and made, while in the lathe, a fine line around the centre of the ball where the centre of the branch is to come, as shown in [Fig. 2800] by the line a, we make a prick point (with a scriber) at each crossing of the line a and the joint or parting of the pattern. We then mount the body upon a lathe chuck, in the manner shown in [Fig. 2802]. A point centre should be placed in the lathe and should come exactly even with the line a. In [Fig. 2802], v v are two V-blocks made to receive the core prints. These Vs are screwed to the lathe chuck, and the pattern is held to them by two thin straps of iron, placed over the core prints and fastened to the Vs by screws. If the chuck and centre point run true, the V-blocks are of equal height, and the core prints are equal in diameter, the prick point opposite to the one placed to the centre point will run quite true; and we may face off the ball or body to the required diameter of branch, and bore the recess to receive the same. We make the holes in the flanges of the same size as the core prints; but we should not check in the print, because, if a flange with a different length of hub were substituted, it would be a disadvantage. To obtain the half flanges, we take a chuck and face it off true in the lathe; then, with a fine scriber point, we mark the centre while the chuck is revolving. We then stop the lathe, and, placing a straight-edge to intersect the chuck centre, we draw a straight line across the chuck face. We then take two pieces suitable for the half flanges, and plane up one flat side and one edge of each piece. If the flanges are not large ones, they may be planed all at once in a long strip. We place the pieces in pairs, and mark on each pair a circle a little larger than the required finished size of flange. We then fix each pair to the chuck, with the planed faces against the chuck, and the planed edges placed in contact, their joint coming exactly even with the straight line marked on the chuck face, and we may then turn them as though they were made in one piece and to the requisite size.
Fig. 2803.
“In [Fig. 2803] we have a representation of one half of a suitable core box, the other half being exactly the same, with the exception that the position of the internal partition is reversed. To get out this core box, we plane up two pieces of exactly the same size and length as the pattern, and of such width and thickness as will give sufficient strength around the sphere, allowing space for the third opening. After pegging these two pieces together, we gauge, on the joint face of each, lines representing the centres of the openings and the centre of the sphere. We then chuck them (separately) in the lathe, and turn out the half sphere. We next place the two halves together, and chuck the block so formed in the three positions necessary to bore out the openings; or if preferred, we may pare them out. The partition (a, in [Fig. 2803]) follows the roundness of the centre hole, and is on that account more difficult to extract from the core than if it were straight and vertical. When, however, the partitions are of this curved form, the pieces of which they are formed are composed of metal, brass being generally preferred. Patterns have in this case to be made wherefrom to cast these pieces, and they may be made as follows: First, two half pieces are turned; each is then cut away so as to leave the shape as shown at a in the same figure, and is then fitted into the spherical recess in the core box, letting each down until both are nearly but not quite level. The two wing pieces are then fastened on, and this pattern is complete. When the pieces are cast, they must be filed to fit the core box, and finished off level with its joint face, a small hole being drilled in the centre, and a pin being driven through the piece and into the box to steady the corners. We then saw the pieces in halves with a very fine saw.
Fig. 2804.
“If the partition, instead of following the roundness of the valve seat, is made straight, the construction of the core box is much more simple. In this case, a zigzag mortice is made clear through each half of the box, its size and shape being that of the required partition. [Fig. 2804] represents a half-core box of this kind. A piece of wood a is fixed, as shown, to the partition, to enable the core maker to draw it out before removing the core from the box. The mortice for the partition should be turned out before the half-spherical recess, the mortice being temporarily plugged with wood to render easy the operation of turning.