In the first of the two methods of making the cast-iron roll, Fig. 372, to be considered, the steel shaft is placed in the mold, and, having been spotted with a drill on the portions which are in the hubs, is practically bonded with the hubs.
The split pattern illustrated in Fig. 373 is constructed of wide lagging nailed and glued to heads. The core prints are assembled as separate members and fastened to the body of the pattern with wooden screws. The pattern is to be assembled complete with dowel pins, and the halves are held together by metal lathe centers, such as considered on similar work in Part II, Pattern Making.
The core box can be made of glued stock, as shown in Fig. 374, or a skeleton form of construction can be used if the roll is very large. The glued stock illustrated in this figure will probably stand up under the wear and tear of the foundry longer than the skeleton construction. Glue the bark side and the heart side of adjoining pieces of stock together, and the center pieces may be made of narrow stock, thus saving considerable material.
Cut the inside to a semicircle with a core-box plane. At g and i the stock is mortised to receive the ends of the arm pattern which is illustrated in Fig. 375. Two patterns will be required of this part as shown in gg, Fig. 374. The dimension e, Fig. 375, should be slightly larger than the diameter of the steel shaft. The part j, Fig. 374, which fits into the recesses e of the arm pattern is semicircular in section, and forms the recess in which the steel shaft is placed. The parts h h h h are patterns of the gate. They are not fastened to the arm pattern but are bedded in the top face of the core.
After ramming the core and bedding in the parts h and j, these parts together with the arm pattern are drawn, and the space is filled with molding sand. This molding sand prevents the core sand from settling when the core has been turned over onto its flat side. When pasting the halves together the steel shaft is placed in position.
The mold is cast on end, the sprues being connected to the gate h. The metal passes through the upper hub, then on into the lower hub and out through the arms, filling the rim; in this manner the steel shaft is brought to a very high temperature, which fuses the shaft with the hub castings and makes a very firm joint.