CHAPTER XII.

EXAMPLES IN THIN WORK.

In the examples we have hitherto presented to the reader, we have supposed the pattern to be of such substance or thickness, as to be able to bear the pressure of the sand being rammed about it in molding, without breaking or altering its form; but this is not always the The parts of a stove, for instance, are cast often less than inch in thickness; the same may be said of most of the ornamental ironwork used in architecture, and even

case.

cornices and window sills range only about

or inch thick. It is true that for this kind of work metal patterns are almost invariably used; but for the pattern maker this is indifferent, as wood patterns have to be made from which the metal patterns are to be cast. Take, for example, the window sill, shown in section in Fig. 187. To enable it to withstand the pressure of the sand, while ramming, we must fill the interior with a form or block,

shown at F, which is to be used in conjunction with the board B. This form and board are no less useful to the pattern maker than to the molder; for let the form be once obtained of the proper size and shape, and the construction of the pattern is so far simplified as to be merely a covering of this form with wood slightly thinner than the required thickness of metal. Most thin work is made in this manner, especially if the patterns are of such size or shape as to need the joining together of many pieces. It is not the pattern itself that demands our first attention, but rather the form that supports it.

Thin work demands great care and patience, on account of its fragile nature. Scarcely any hold can be obtained for nails; and though the best glue is used, it cannot always be relied upon. Dovetails for square corners, if they are end wood to end wood, will be found very superior to glued joints. Furthermore, as few joints should be made as possible, and the pattern should be well protected by several coats of varnish. In working out thin moldingsas for instance, the portion of the sill from a to b, which should be of one piece-we plane up a piece of a suitable width and thickness, and trace the outline of the molding

Fig.188.

upon each end of the piece; then, as it lies flat upon the bench, we work out on one side to the lines which will fit the form, as in Fig. 188, and then, by temporarily fastening the piece to the form, F,

to

give it proper support, we are enabled to work out the opposite side to the required shape. In working out thin moldings, a circular saw with an adjustable table will be of great assistance, as by its means we may make a series of saw cuts so close together as practically to take out half the stuff, and form an excellent guide for cutting away

the other half (see Fig. 188). The part from a to c, Fig. 187, should not be formed by gluing thin stuff together at the obtuse angle, but should be of one piece. Fig. 189 is a section of a cornice lying upon its bed or follower board, B; it may be made of one piece, as in the previous example.

Fig.189.

In molding work of this kind, the procedure is as follows: The board, B, with the form and pattern, is placed upon a level bed of sand, so that it may not wind or twist under the weight that is to be put upon it, which will consist of the nowel rammed full of sand. The board and nowel are fastened together by clamps, and, the ramming finished, the whole is turned over; the board and form are then removed. There is no longer any necessity for the support of the latter, as

the sand, having been once rammed, does not press upon the pattern to its injury, but keeps its position, and becomes a good and sufficient support to it during the ramming up of the cope, which is now placed in position, and the molding continued in the usual manner.

Fig.190

Instead of the form, F, which fills the interior of the pattern, we may provide a strong enveloping form, as shown in Fig. 190; the difference is that the reverse side of the

casting will be uppermost as compared with the other case. The form must fit that side of the pattern which we wish to come next the cope. Forms of an irregular or difficult shape are often advantageously made by simply pouring plaster of Paris into the patterns for which they are intended. A great deal of thin work is formed by dry sand coring, often from necessity; but when practicable, the dry sand core is discarded, and the pattern made to leave its own core. This insures greater accuracy, is cheaper, and causes the interior surface of the casting to be the same as the exterior. When dry sand cores are employed, there is no difference between thin work and thick, and therefore the methods described in former pages are a sufficient explanation of the process.

CHAPTER XIII.

SWEEP AND LOAM WORK.

The above title applies to a class of work, generally of large size, in which boards or sweeps, fixed to a revolving spindle, serve instead of patterns to form the molds. This arrangement, of course, will only produce circular molds; patterns may, however, be used in conjunction with the sweeps, as we shall endeavor to illustrate further on. The spindle above named is a light vertical shaft, revolving in a step below and a bearing overhead; when a part of a mold has been swept up, the spindle can be raised out of the step sufficiently to enable the work to be removed and preparations for the next piece substituted.

Fig.191.

Let it be required to produce a casting, such as is shown in Fig. 191—a sort of pan or boiler, often used. Fig. 194 is a sectional view of the mold complete. It is formed of two parts, the lower being called the "seat," and the upper the "cope." Figs. 192 and 193 illustrate the method of forming each of those parts. The material used by the founder is called loam-a clayey, plastic composition, very soft. After a certain quantity of this material has been piled up, the sweep is revolved; it shears down the high places and indicates the holes or hollows. more material is placed, and the sweep is passed round again; and so on until the job is perfected. It will be noticed in Fig. 194, that the two parts of the mold are retained in their proper position by a projection on one

Into the latter