Pattern makers receive drawings of finished iron-work; from these drawings they must lay out and construct the wood-work necessary to obtain molds for the castings.

Fig. 1 represents a cast-iron pillow-block, to receive an inch-shaft; Fig. 2, the plan of the box without the cap. The surfaces through, from a to b, Fig. 1, are to be finished.

Fig. 3 represents the pattern for the cap; it is made of four pieces, a, b, c, d, nailed together.

The measures taken from the drawings, or specifications, are increased a small amount, about 1/8" to 1', to allow for shrinkage of the iron.

Those surfaces which are to be finished should be about 1/16" thicker than shown in the drawings. In Fig. 3 the wood beyond the broken line, e, e, shows the allowance made on the pattern for finishing.

The smoothest surface, containing the least number of blowholes, on a casting, is the one which was down; therefore, the pattern must be built with that in view. In order to facilitate drawing the pattern from the sand, it should have its vertical sides slightly inclined and very smooth.

The base, Fig. 4, is made of the several pieces, a, b, c, d, and e, to secure smoother surfaces than could be obtained by cutting the pattern from a solid block. The lower part of the piece, d, may be made separately.

The holes for the bolts are either to be bored in the metal or cored. In the latter case, a core-print, f, is fastened in the proper place, and the molder inserts in the mold a core of the proper size.

The box is to have hollows, to receive Babbit metal linings; these hollows must be cored out; c, Fig. 3, and e, Fig. 4, are the core-prints, and Fig. 6, the core-box for the hollows, which are in-dicated by broken lines in Figs. 3, 4, and 5. The core-box is made of five pieces; the block, a, with the thin pieces, b, nailed to its ends; the pieces, c, c, held in position by dowels, are removed, to free the core.

The pattern has its nail-holes filled with wax or putty, and is varnished with shellac dissolved in alcohol. The core-prints are covered with shellac varnish in which lamp-black has been mixed.

Ex. 37.

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6