Before taking up the design and construction of the parts required to adapt the patterns to machine molding, the conditions presented by the hand-molded patterns may be briefly considered. The working drawing, without dimensions, of a holder frame is illustrated in Fig. 308; and in Fig. 309 is a view of the iron-gated patterns. The cover is designed to pass endwise onto the holder frame, as indicated in Fig. 308, the bevel on the inside of the lugs o being molded with a dry-sand core, and the round recesses in the holder also being molded with a dry-sand core. The least imperfection to these dry-sand cores means that considerable fitting has to be done to get the parts assembled. With the machine-molded castings, the castings and the hard-wood bearings are literally thrown together.
Fig. 308. Working Drawing of Holder Frame that Requires Side Draw.
Fig. 309. Original Gated Patterns, Showing First Attempt to Increase Production. They Require Dry-Sand Core for Each Costing. With Machine-Maunted Patterns, Entire Mold Is Made in Green Sand.
Fig. 310. Nowel or Drag Stripping-Plate Hand-Rammed Making Machine.
Fig. 312. End Elevation of Pattern Equipment for Reid Hand-Rammed Stripping-Plale Machine.
In Fig. 310 is illustrated the drag machine, and in Fig. 311, the machine with the pattern in position for molding. An end view of the stripping plate, draw plate, and assembled mechanism of the drag machine is illustrated in Fig. 312, and Fig. 313 is a section through the center of one pattern. This machine is fitted to make four molds which are all gated to one sprue. The mechanism unit is duplicated for each pattern.
The proposition with this drag machine is to draw the pattern at an angle of about 30 degrees from the vertical, and therefore the pattern cannot be bolted directly to the draw plate a. To obtain space beneath the stripping plate to install the mechanism spacers are interposed between the top of the machine frame and the underside of the stripping plate, as shown at m and m. In Fig. 313 the pattern is illustrated in its raised position, and the dotted lines illustrate the position of the draw plate and levers when the pattern has been drawn.
A perspective sketch of the stripping plate is illustrated in Fig. 314, part of the casting having been broken away to illustrate the position of the holes through which the pattern is drawn, and Fig. 315 is a sketch of the pattern for the stripping plate. Small blocks o, of cast iron or steel are to be fastened at each end of the depression after the machine planing is completed.
Fig. 314. Diagram of Stripping Plate. One End Broken to Show Holes through Which Pattern Is Drawn.
The plate is made of narrow strips of stock, glued so as to reverse the heart side of adjoining pieces. It will not be necessary to spline these patterns, for only one casting is usually required and the pattern is generally molded as soon as it is completed.
What is to be the top of the casting is molded in the dry mold so as to be sure of obtaining a clear surface. Most of the causes of imperfections in castings rise to the top of the mold while the metal is being poured, and thus, if there are gas or dirt blowholes in a casting, they will be found in the cope side of the casting. The casting is parted where shown, and the cope part of the pattern should be located on the drag with two dowel pins.
The core for the cope shall be made in a skeleton core box. No sketch is shown of this core box, but its construction would be similar to the core box for the part g, illustrated in Fig. 318. Fig. 316 illustrates the dry-sand core used in the drag mold, and Fig. 317 the core box for the core. This sketch shows the box partly assembled and cut away so as to illustrate the construction. When it is certain that the parts are accurately cut to the required dimensions, they should be nailed and glued. One end is fastened to one side of the box, and the opposite end to the other side. No dowel pins are required as the shoulder holds the sides in alignment. Produce a slight draft to the parts forming the holes p, and a filing finish of about 1/12 inch should he allowed on the sides of these holes.
Fig. 318. Casting Puttern and Core Box for Part e, Fig. 312.
The sketches of the parts g and k, Figs. 318 and 319, should readily explain themselves. A dry-sand core is used to mold the part g, a sketch of the pattern and skeleton core box being given in Fig. 318. This was deemed necessary owing to the length of the dimension g1. At best, the pattern would be quite fragile. The pattern for the part k. Fig. 319, should he made without a core print.
The master pattern and core box for the part c, Fig. 320, which is the pattern for the drag machine, are illustrated in Figs. 321 and 322. When making the wood pattern, double shrink should be allowed, and a filing finish of not over 1/32 inch should be added to all surfaces. The sketch of the core box shows a construction similar to that of those described in Part II, Pattern Making. The round hole at the lower end of the casting is to be finished to slide easily over the stool.
Fig. 320. Casting for Pattern e, Fig. 312.