F. W. PUTNAM

It often becomes necessary for the pattern maker to make a pattern for a casting that is to be hollow, or to have a hole through it, in which case it is customary to make the pattern of such form that it will leave a body of sand in the mold about which the metal will flow. The body of sand left in the mold forms the desired hole or opening, as shown at a, Fig. 9. This body of sand projecting up into the mold to form the opening in the casting is a called a core, and may be left by the pattern itself, as in Fig. 9, or it may be made in a separate device, called a core box, and placed in the mold after the pattern has been drawn out. Cores made by the pattern alone are called green sand core.

Fig. 9 represents a mold made by a pattern of the shape shown in Fig. 10, which shows the casting of shoe. The pattern for this shoe will be the same shape as the casting, the necessary allowance being made in the size of the pattern to cover the shrinkage and finish of the casting.

Shoe Patter

For this pattern use a piece of clean dry pine. Plane the block to the required width and thickness and square the ends to the desired length. The first side planed up should be carefully tested with a try square; when found to be perfectly straight and true, it should be marked with two short parallel lines. This side is called the face side, and we will generally, in this pattern work, consider the top surface of the pattern, as it is drawn from the mold, to be the face side. The next side is planed up it at right angles to the face side and is called the joint side. This side is tested with the try square, and when found to be straight and exactly at right angles to the face side is marked with one short mark. The block is gauged for thickness from the face side, and the third side is then planed down to the gauge line and is tested from the joint side.

Fig. 9. Mold Made By Pattern.

The block is gauged for width from the joint side, and the fourth side is planed down to this gauge line, being tested from the third side. Gauging should always be done from the face and

Fig. 10. Pattern For Shoe.

joint sides of the block. In setting the gauge always measure the distance from the spur to the head with a rule, as the spur may easily have been bent and so make the scale which is cut on the bar of the gauge of no practical value, the zero point on the scale originally coming directly in line with the spur. The marks which are to be made on the face and joint sides of the block are called witness marks and are shown in Fig. 10.

Having finished the block to the required size, mark out the rectangular hole which is to be cut through the block as indicated by the dotted lines in the right end view of Fig. 10. The lines should be marked on both the top and bottom faces of the block, making sure that both the top rectangles are correctly located and of the right dimensions. Holding the block in a vise, next bore fuor holes with a 1/4" auger bit, one in each corner of the rectangle, the edge of the hole coming 1/16" inside the rectangle. In boring holes advance the bit until the spur just pierces the opposite surface, then remove the bit, turn the block round in vice and bore back. In this way there should be no splintered surfaces as a result of boring. A 5/8" auger bit should next be used, six holes being bored, one next each short side, and two next each long side, 1/16" being left in each case from the edge of the bit holes to the border lines of the rectangle.

The hole is to be finished with a chisel, following the directions given in the last article. This hole should first be squared up from the face side, with no allowance for draft. Remembering that the face side is to be the top side of the pattern, the allowance for draft is next made. The sides of the hole may be tapered with a flat wood rasp, in which case a file with one narrow edge "dead smooth" should be used. Such a file is generally known as a safety edge file. The safety edge is brought against the corners of the hole and prevents the file from digging in and so spoiling the shape of the hole. The sides of this hole should be carefully tested for draft, being very sure that there is no back draft. The draft allowance on the outside surfaces is finished last.

In clamping the pattern in the vise for chiselling, it will be found advisable to clamp a block against the pattern, thus preventing the wood from being broken away on the back surface of the pattern. A very little practice of this sort in the use of chisels, will be sufficient to warn the amateur that his chisels must be kept sharp, with a perfectly straight bevel not too blunt, and a straight edge.