The work of the moulder differs from that of the carpenter, blacksmith or machinist. The blacksmith can see with each blow of his hammer how his work is progressing; the machinist has his work constantly under his eye so that he sees just what is being done even with the finest cut. But with the moulder, the progress of his work to some extent is not visible. He makes his moulds and cores but the progress of his work cannot be fully determined until the casting is completed. For this reason the moulder must work with great care; his skill comes largely from his own experience and that of his fellows. Knowing "the reason why" is of as much benefit in this work as in any other.
It is impossible to give explicit directions as to the force of the blow to be given to the rammer. This must be left to the judgment of the workman. He will soon learn to gauge the blow according to the work to be done. The general principles of ramming may be roughly stated to be:
The deeper the body of sand the harder the ramming.
The hardest ramming must be done near the lowest point of the sides of the moulds.
The lightest ramming should be done near the highest point of the sides of the mould.
To these statements it may be added, that light ramming continued, until the sand is in a proper state of compactness, will give better results than hard ramming for a shorter time. Evenness in the blows is of the greatest importance. Any bottom section of a mould that is to have a pressure put upon it by a rapid flow of molten metal will stand harder ramming than where it is to be covered over slowly. Hard ramming causes more trouble than light. The rammer should never be allowed strike the pattern.
The general method of making a mould is the same for all patterns, but there is an endless variety in the detail. As a simple example take the gland illustrated in Fig. 56 of "Pattern Making" and reproduced here in Fig. 23.
First select a flask of a suitable size. It should be at least 8 inches larger each way than the diameter of the pattern, and 2½ inches deeper. This leaves 4 inches of sand upon each side and 2½ Inches at the bottom. The flask consists of the two parts, the cope and drag or nowel to which must be added a moulding board. This moulding board is used repeatedly for successive moulds. It consists of smooth boards fastened together with cleats as in Fig. 24, and has one plain surface. The moulding board is laid in a level position on the floor with the plain surface uppermost. The pattern is placed in the middle of the board, with the side down which is to be at the parting line between the cope and drag. The drag should then be set on the moulding board (Fig. 25) bottom up. It must be adjusted so as to stand evenly about the pattern. Fill a riddle with sand and sift it over the pattern until it is entirely covered. Where there is to be a core formed of green sand, as in this case, the hole in the pattern must be filled with sifted sand. Tuck this sand down snugly into the hole before commencing to ram. When the ramming is completed scrape off the sand that projects beyond the edge of the drag, lay another board on top to hold the sand in position, and clamp the drag and the two boards together as in Fig, 26.
The clamps used for this purpose should be strongly made of iron about 1 inch square and of the shape shown in Fig. 27. They should be long enough to slip easily over board and drag and be held by wedges driven in as shown in Fig. 26.
When the drag and moulding boards have been clamped together the whole should be turned over and the moulding board removed. This exposes the surface of the sand with the pattern on top. Examine the mould carefully to see if the sand lies close about the edges of the pattern. If it does not, mend it by the addition of sand where needed. Do this work with the fingers and only use the trowel for smoothing.
After this face of the mould is made all right, sprinkle the whole surface with sharp sand, which is then called parting sand. This will prevent the sand of the cope from adhering to that in the drag. If the sand adheres the cope and the drag can not be separated and the pattern removed without injuring the mould.
After placing the cope in place, sift in enough sand to cover the upper surface of the drag, then shovel in enough to fill the same and ram. In ramming the cope be careful that the rammer does not strike the bars.
When the cope has been rammed and the superfluous sand removed from the top, it is lifted off and laid bottom up. The parting sand is then dusted from the faces of cope and drag. The pattern may now be removed. It is usually advisable to wet the swab and draw it around the edge of the pattern. This stiffens the sand and prevents it from breaking away when the pattern .starts. Great care should always be exercised in the use of the swab. If too much water is used it will cause blowing when the iron is poured. If it is necessary to make the sand very damp, it should I* dried somewhat before pouring. The pattern is lifted out of the sand by screwing a lifter into the lifting plate, if there is one. If no lifting plate has been put on the pattern, a sharp pointed lifter is driven into the wood. This is rapped gently to and fro, while being pulled. As soon as the pattern starts the rapping may stop. Be careful that the pattern is lifted vertically and does not strike the surface of the sand. The mould is now made and only requires finishing and blacking.