and the pattern laid in center of same, the top edge of the form is even with the center line of pattern if it were cut in halves. This box form is now filled with dry sand, all around the pattern and up to the edge; this is simply to support the division plate at the proper point, and to make a solid support for same so the sand mixture that is to make the mold may be tamped above it; the division plates are laid upon this form, that is filled with dry sand and the first section of flask placed upon that; the drag or first section of flask is now filled with the sand mixture in the ordinary manner, as described for making mold. The dry sand in lower box is simply to hold the pattern solid and exactly in center while this first section of mold is made.

As soon as drag is filled with sand mixture, a coverboard is placed upon same and the whole thing reversed or turned over, bringing the box form with the dry sand uppermost; this is now removed, thus exposing the other half of pattern. The cope or upper section of flask is now placed over this and the second section of mold made with the sand mixture; in making

this section cover the pattern carefully with the sifted dry sand as when the cope is lifted it must part from the pattern. Either the pattern, which is in one piece, must draw from the cope or the drag section of flask, as you grasp the metal division plate with the cope or upper section of flask and lift both together, thus parting the two sections of mold and at the same time drawing the pattern from one section of the mold.

This is a necessary part of the work where it is an impossibility to divide the pattern, and the pattern is in such shape that exactly onehalf must be imprinted in each section of mold; with concrete patterns or those made of metal this manner of dividing the mold will be found invaluable.

The same idea may be adapted to the use of wood patterns that are in halves; the two halves of the pattern are nailed to opposite sides of a coverboard, so they will be exactly in line with each other, but on opposite sides of the board; in making the first section of mold, the coverboard rests upon an empty section of flask,

and by reversing same brings the other half of pattern uppermost, when it is desired to make the second section of mold.

In preparing clay models for a two-piece pattern, it is of great advantage to make exactly one-half of the model on each of two modeling boards; these should be spaced so that the center of model is exactly in the center of modeling board and a line drawn around same, on the board, to designate where the section of flask is to be placed. This is important, so that each section of flask will be placed at the same distance from the model at all points, thus bringing the model in the exact center of each section of flask, and when the two sections of flask are placed together, for molding work, the impressions of model will meet perfectly, as if the pattern were in one piece.

This method permits easy work in using clay models, as one-half of a clay model is quite easily built up on the modeling board, when impossible to model the entire piece and have in shape for making a mold from same; again

the clay model does not require handling, the mold or impression is taken of same as it rests on the modeling board, hence the danger of injury to model is lessened and a more successful mold assured.

CHAPTER VII

CORES, HOW TO MAKE AND USE WITH SAND MOLDS

THE proper making and use of cores is one of the most difficult operations connected with the molding of concrete with sand molds. The core must be carefully planned with a view to the fact that it must remain in position with exactness, while the concrete is being poured and must be so planned that it can be easily removed, if a hard baked core is employed. For all small cores that are of such shape as to permit their removal from the work in one piece, it is advisable to make them of a sand mixture that permits hardening or baking; this is an advantage from the fact that a green sand core is very apt to be swept away, or a portion of same disintegrated by the action of the concrete poured into mold, which would not be the case with one of a hardened mate