Preliminary to making the durable iron core box. Fig. 275, prepare stock for the flanges for the wooden core box 2/8 inch thick, obtaining the form and dimensions from the double-shrink zinc template, and making the inside edge £ inch outside of the template so as to run the stock for the outside wall from bottom to top, as shown in Fig. 276. The perspective sketches in Figs. 275 and 276 illustrate the appearance of these flanges, the pieces j and k being sawed to the full length and the tenons produced with the machine saw. The grain of the stock should be as nearly parallel to the length of each piece as possible. The layout for these flanges need only be made on one piece of stock. Nail two or more pieces of stock together, as the needs may be, band sawing all from the one layout. In nailing stock together for this purpose, use two slim finish nails and drive them one at each end - not near each other at the center, and not in the waste stock. These same nails will then hold the pieces firmly together while the edges are being trimmed smooth and true. Should the depth h be over 12 inches, an intermediate flange should be made and placed between the openings m and m. Glue j and j1, together, using care that the angle between them is correct. A slight draft should be made on these flanges, the outside edges being the thinnest. With stock for the pieces ww dressed to size, the flanges are nailed and glued together, as shown in Fig. 276. All parts should be hand-planed before they are assembled. Always nail each joint in correct location - driving the nails only far enough to locate each piece - before the glue is applied. When the nails are driven through the joint after the glue is applied, the glue acts as a. lubricant for a few seconds, causing the parts to slip, and some of the glue will be pressed out of the joint so as to obscure the construction lines, with the result that often a joint will be finally fastened together a little out of position.
Fig. 275. Diagram of Completed Iron Core Box.
Another rule that must be followed by the accurate pattern maker is never to use a lead pencil or a scratch awl for marking center and construction lines; use a thin pointed knife and make sharp deep lines. Pencil lines are too broad, and the awl tears the stock. Center lines should always show on the surface of the completed pattern, but construction lines should not, unless they mark the location of some future alteration or addition. The center lines are necessary for checking the dimensions of the pattern.
Fig. 276. Flanges and Partially Assembled Rear Half of Core-Box Pattern.
Having the flanges assembled, nail and glue the walls x in place. This stock is to be 1/4 inch thick, with the grain running vertically. Where the radius is short, narrow pieces should be used as shown. The work on the opposite half should be carried on at the same time. Smooth the inside of each half and the whole to fit the template.
Fig. 277. Vertical Section of Core Box on Line i i, Fig. 274.
The slots mm shall be carefully laid out to the dimensions a and b, shown in the vertical section of the core box, Fig, 277. Bore holes at each end, and saw with a thin backless saw. It will be necessary to start the cut with a keyhole saw. The edges should be trimmed with a chisel and have a decided draft to each side, as the slot is molded with a green-sand core. See that there is no back draft at the ends, and to prevent this, the slot should he made shorter than the required width, being filed out in the casting.
A pattern for the draw pieces l and l is to be made as shown in Figs. 274, 277, and 278; the radii c and d being shown in Fig. 272. The thickness is u, and an enlargement at one end is provided to serve as a handle. Two castings from this pattern are required.
A cast-iron bottom and top will require a right- and left-hand pattern, illustrated in Fig. 279. Stock should be glued of narrow pieces, say 3 inches wide, with the heart side of the stock reversed, and should be cut to the form shown in Figs. 275 and 279. The small blocks or lugs are so placed that they center the bottom with the sides. This bottom can be centered with the sides by dowel pins in holes drilled through the flange. However, as the bottom and top should extend outside of the flanges, to provide means for lifting, there will be plenty of room for these lugs.
Fig. 278. Draw Pieces for Core Box.
The piece y which forms the mold for the upper and lower crown is glued to the plate, and stock should be removed with carving gouges from the opposite side to prevent as much weight as possible. This piece is sawed to the form of the template and the radii c and d. The face shall be carved to the bevel and round cor-ner shown in Fig. 272. A radial template of thin wood can be made to show the form of this surface. If the template with its edge coated with blue chalk is passed over this surface, it will indicate the high spots. These can be reduced with the carving gouges until nearly to dimension, when the surface should be smoothed with one of the flat iron spokeshaves.
Stop-offs, shown in Fig. 279, should be screwed to the outside of these wooden patterns to prevent warping. They should have liberal draft, say about 3 inches to the foot, and should be finished to some color different from the body or core-print portions of the pattern. The imprints of these stop-offs are filled in after the pattern is drawn, and do not come in the casting for the metal core box.
The block p, Fig. 279, forms a pouring gate and generally is used in four of the cores. It can be made of hard wood or iron, and is held in place by two small steel dowels. The pattern maker should consult the molder for the dimensions of this gate.
Fig. 279. Bottom of Vane Core Box.
The gate continuation should be made of a dry-sand core, which is shown in Fig. 286, and the core box for which is illustrated in Figs.280 and 281.
Fig. 280. Perspective View of Core Box for Gate with Side Removed.
The top of the core box is made to the same dimensions as the bottom, but is made the opposite hand. The gate p is to be fitted to both bottom and top.
These guide rings are made both for turbines which rotate in a right-hand direction and also for left-hand rotation. The same core box can be used for both; consequently what is the bottom of the core for the right-hand turbine becomes the top of a left-hand turbine.
Fig. 281. Details of Core Box for Gate.
The hooks for locking the box together, while ramming the core, are iron or soft-steel forgings and can be fitted by the metal-pattern maker. In ramming the core, the sides are clamped together and placed on the bottom. Tore sand is rammed to the underside of the lower draw piece, and is then struck off with the strike shown in Fig. 277. Inserting the draw piece, the ramming goes on and the strike is again used when the upper draw piece is reached. With both draw pieces in place, the box is rammed to the top. Using the strike, it is possible to ram the sand firmly under each draw piece, where it would be rather difficult to ram in any other way. Sand is now cut out at the top nearly to the shape of the top crown, and the top of the core box pressed into place. This top may have to be removed several times until the right amount of sand has been removed. When the top of the core is completed, the space forming the top crown of the ring is filled with green sand, a drying plate placed on top and the core box and all are rolled over. The bottom can now be removed and the draw pieces drawn out through the side, forming the mold for the intermediate crowns ll, Fig. 272. The sides can now be taken from the core, which appears as in Fig. 282.
Fig. 284. Details of Bottom Core.
The core box for the bottom core is shown in Fig. 283, and the core in Fig. 284, and in the radial section of the assembled cores, Fig. 286. The number of flat cores to go around should not be the same as the number of vane cores, but enough to give an outside chord length of about 20 inches. The dimensions of this core, shown in Fig. 284, are not arbitrary, and should be made to correspond to the requirements of the weight of the vane cores. The illustration of the core box shows the construction; the thickness of the bottom should be about 7/8 inch, and the sides about 1 1/4 inch. The bottom can be made of pine or mahogany, and the sides of mahogany, maple, or birch.
Fig. 285. Gage for Setting Bottom Cores.
A measuring stick, Fig. 285, must be provided to locate the bottom cores. The semicircular notch at the inner end shall be the diameter of the spindle, which should be about 3 inches, and a small block should be nailed and glued on, or a notch cut in one edge, at the outer end. The radius r should be the same as the inner radius of the vane cores.
The covering core x, in Fig. 286, can be made in the core box for the bottom core by fitting a loose piece z, as shown in Fig. 283, into the core box to stop off the shoulder.
After bedding the drag flask in the foundry floor, a spindle made of a piece of steel shafting, bolted in the hub of an old pulley, or any other method which will hold the spindle in a vertical position, is bedded in the sand at the center of the flask. The sand inside the flask is rammed hard and struck off level to form what is called the bed. The spindle must stand vertical to this bed. Place the bottom cores on the bed and set them concentric with the spindle, using the measuring or gage stick, Fig. 285. Upon these cores the vane cores are placed, and the covering cores are placed on top of the vane cores. The spindle then is drawn out and the gate cores set. A portion of the shoulder on the bottom cores will be cut out to complete the gate into the mold, as shown in the assembly, Fig. 286. The sprue is made with a tapering wooden pattern placed in position at the junction of the gate cores. Iron or wood cheek flasks are placed outside of the cores, and rammed full of molding sand. The cores are thus held securely in place and the mold is made without having to turn the drag mold over, which is quite an advantage in heavy work of this class.