The fillets spoken of in connection with Fig. 195 are used in all except the most simple patterns. They consist of a small quarter curve varying in size from 1/8-inch radius upward, depending on the size of the pattern and the room they can be allowed to occupy. They should be placed in corners so that there may be no sudden changes in the direction of the surface of the casting, which causes weakness, the fillets adding greatly to the strength of the casting. Round corners and fillets should be used wherever possible, as they make a cleaner mold, the metal flows into and through the mold easier, the metal is not so liable to wash away the sand at the corners, and the shrinkage strains of the cooling metal are not so liable to start cracks at the corners.
Fig. 197. Section of Wood Fillet.
These fillets are made in various ways, the wooden fillet, cut as in Fig. 197, being commonly used for all long straight angles, or for very flat curves to which it can be bent. On large patterns intended for one or two castings, the fillets are three-sided pieces of stock nailed into the corner, giving a chamfered corner to the mold. The molder slicks this corner if necessary.
Wood fillets, where they can be built in, are more durable, and should be used on all patterns intended to be standard, as in Fig. 198.
For irregular angles and for short radius curves, beeswax was formerly used, but the modern leather fillet has almost entirely superseded beeswax and other material for this purpose. It is easily applied, shaping and adapting itself to any and all positions and angles. It can be bought in all sizes from 1/8 inch up, the sizes running by sixteenths.
The method of applying it is to cut it to the necessary length and lay it on a board where the glue can be easily brushed over it. It is then laid in the angle and rubbed into position by means of a dowel rod, the end of which must be rounded. The dowel rod must be of such size as to impart the required curve to the soft pliable leather fillet. As soon as the fillet is rubbed into position, all surplus glue must immediately be wiped off before it sets. This is easily done with a small piece of waste or a rag dipped in the hot water of the outer gluepot and wrung out nearly dry, care being taken not to wet any part of the pattern more than can possibly be helped, after which it must at once be wiped dry. These leather fillets will be found more pliable and more easily placed and rubbed into position if the glue used is first allowed to cool slightly. Very hot glue stiffens and crinkles the leather, causing it to work hard.
For patterns intended for temporary use, fillets made of linseed oil putty are often used. While this type takes some days to become hard, it is very low in cost and can be used for patterns of this class to good advantage.