The patterns for the larger pipes or columns are to be glued up, as shown in Fig. 224, and, for turning, the two halves are held together by means of lathe dogs such as shown in Fig. 206. The treatment of this glued up stock in the lathe, is the same as employed in turning the small pipe shown in Fig. 220. The method of constructing the core box for this or similar patterns is shown at b, Fig. 224. Tees, elbows, and other bends and connections, when large, are built up in a similar way.

Hollow Construction

For large cylinders, a much lighter and simpler method of constructing the pattern is shown in Fig. 225. For each half of the pattern the two end disks and the middle semicircular disk are connected together by a strong center bar, which is fitted, glued, and screwed into each, serving not only to strengthen the pattern, but also to hold the connecting dowel pins. When the two halves of the pattern are clamped together, it serves also as a secure mean3 of centering in the lathe.

The staves forming the body of the cylinder are fitted and glued to each other, and screwed or nailed to the disks. After the cylinder has been turned, the core prints and flanges are built up and turned separately, and glued and screwed to the ends of the cylinder from the inside of the end disks.

Fig. 226 illustrates still another and better method of building up the cylinder and core prints in one piece and completing the hole at a single turning. The core prints, as shown, are staved up first, and then the staves to form the body of the pattern are fitted, glued, and screwed, or nailed, over the ends of those which form the core prints. For long cylinders use one, two, or more middle semicircular disks.

A similar construction for the core box is shown in Fig. 227, and is to be preferred to all others, because, if laid out and built to the exact size, the labor required to reduce the staves to a perfect semicircle of the required radius is very little.

Quantity Production

Patterns for such work as pipe fittings would come under the head of standard patterns, as usually these parts are required in large numbers. The present-day practice of molding patterns for the smaller sizes of pipe fittings is to either have a number of similar patterns gated, Fig. 228, or resort to plate molding and stripping-plate molding machines. Some present-day methods of machine-molding pipe fittings are considered in Part HI, Pattern Making.