It would be a costly matter to make core boxes for long cylindrical cores, such as are used for pipe and similar castings; hence, for such purposes, a core is made as shown in Fig. 84, in which C represents a core for a pipe, having a

socket at one end. It is prepared as follows: Upon the two tressels, A A, is mounted the long tube, DD, which is perforated throughout its entire length with numerous small holes, and which is provided at one end with a crank handle, by means of which it may be revolved as it rests in the two rude V bearings, provided in the top of the tressels, as shown. Upon this tube a layer of rudely twisted straw rope, sufficient to make its diameter assume, from end to end, nearly the required diameter of the core, is coiled. Outside the straw rope there is then applied a coating composed of a mixture of loam and other material sufficient to increase the diameter from end to end, somewhat above finished size. To round up the core even, and make it of the necessary size, the core or loam board, B B, is employed. It is simply a board ranging in thickness

from seven eighths inch upwards, according to its length. One of the edges is cut to the conformation of the required core; and all but about three sixteenths of an inch of the thickness of this edge is beveled off at an angle of about 30°. This board is laid upon the tressels with the beveled edge uppermost, and is held in position by weights placed upon it over the tressels. The core is then revolved by the

Fig. 84.

Fig. 85.

handle in the direction of the arrow, as shown in Fig. 85, in which A represents the tube, B the straw rope, C the loam coating, and D the board. It follows that, as the loam is added, the board will level it off, leaving the surface round and true, and to whatever shape the edge of the board may be made. It is customary to mix with the coating of loam, horse dung, or a substitute therefor, the object of which is as follows: It will be readily perceived that it is a difficult matter in a long casting to give vent to and permit the escape of the air and the gases formed in the mold by the molten metal; but by mixing in with the loam a combustible material, the latter becomes con

sumed during the baking of the core, leaving the latter porous, so that the air and gases can pass from the mold through the loam coating and thence through the straw rope, and find exit through the hollow tube upon which the latter is wound.

CHAPTER V.

EXAMPLES OF SIMPLE LATHE WORK.

Fig.86.

WE may now commence a series of examples, accompa nying each example with the explanations and considerations necessary to, and governing the method of, the construction chosen. Fig. 86 represents a drawing of a gland for which a pattern is required. Now this is a very simple pattern, and yet there are at least six different methods of making it, any of which may be followed, as will appear more clearly to the reader by his glancing over Figs. 87, 89, 90, 92, 93, and £4. The first question is how to deter mine which method is the most suitable. Let us suppose the pattern maker to be uninformed of the purpose the casting is to serve, or how it is to be treated: in such a case he is guided partly by his knowledge of the use of

such patterns, and a consideration of being on the safe side. The form shown in Fig. 87 would suggest itself as being a very ready method of making the pattern; by coring out the hole it can be made parallel, which the drawing seems to require. The advantage of leaving the

hole parallel is that less metal will require to be left for boring, in case it should be necessary; because, if the hole is made taper, the largest end of the bore will require to have the proper amount of allowance to leave metal sufficient to allow the hole to be bored out true, and the smaller end would, therefore, have more than the necessary amount: while just the least taper given to the ex

terior would enable the Fig. 87.

molder to withdraw the

pattern from the mold. Made in this way, it would be molded as shown in Fig. 88, with the flange uppermost, because almost the whole of the pattern would be imbedded in the lower part of the flask, the top core print being all that would be contained in the

cope; and even this many be omitted if the hole requires to be bored, since the lower core print will hold the core sufficiently secure in small work, unless the core is requir ed to be very true. The parting of the mold (at C D, in Fig. 88) being level with the top face of the flange, much taper should be given to the top print (as shown in Fig. 87), so that the cope may be lifted off easily. Were this however the only reason, we might make the top print like the bottom one, providing we left it on loose, or made it part from the pattern and adjust to its place on the pattern by a taper pin; but another advantage is gained by well tapering the top print, in that it necessitates the tapering of the core print at that end; so that, when the two parts of the mold are being put together- that is to say, when the cope is being put in place- if the core has