The keystones were molded in wooden forms, consisting of one piece, a, forming the top and front; of two side pieces, f, of a bottom consisting of two parts, b and c; and of a back piece, g. The back and side pieces are stiffened with 2×3½-in. pieces, and the front, sides and back are held together by yokes or clamps. The front of the mold was the only portion calling for particular work, and this was made of boards laminated together.
The bracket molds consisted of two side pieces provided with grooves for receiving the front and back pieces, and with slots for tie rods clamping the whole mold together. It will be noted also that the side pieces had nailed to them inside a beveled strip to form a groove in each side of the cast block. The purpose of this groove was to provide a bond to hold the bracket more firmly in the adjoining concrete of the wall. The bottom of the mold was formed by a 2-in. plank, and when the concrete had been tamped in place the forms were removed, and the bracket was left on the bottom to set. It may be noted here that a goodly number of the brackets showed a crack at the joint marked x caused by tamping at the point y. In construction the bracket castings were set at proper intervals on the spandrel walls, which had been completed up to the level of the line X Y. The coping course was then built up around the bracket blocks to the level of the bottom of the railing base.
Fig. 288.—Molds for Railings and Ornaments for Concrete Arch Bridge.
The mold or form for the coping course was designed to build the coping in successive sections, and was built up around the bracket blocks, and supported from the centers as shown by the drawings. To form the expansion joints in the coping course there were inserted across the mold at proper intervals a short iron plate ¼ in. thick, cut to fit. The cutting of this plate was found to be a slow operation.
The forms for the base of the railing (Section D) consisted of 1¾-in. stock for the sides, and ¾-in. stock for the slopes. They extended across the arch, and were held together by a very simple though very efficient clamp. This consisted of two 2×3×33-in. pieces nailed to a 2×3×17-in. piece by means of galvanized iron strips. About half-way down the long pieces, a ½-in. rod was run through, and secured up against blocks, h, placed about 56 ins. apart. These blocks were removed as the concrete was put in place. It will be noticed from the cross-section of the railing that the balusters are set into sockets formed in the top of the base course. These sockets were formed by means of the mold shown at W and Z.
In casting the balusters, Section (E), a ⅜-in. cast iron mold, consisting of four iron sides and an iron top, was used. Originally there were two end plates of iron, but it was found more convenient to have the bottom one of wood and allow the cast spindle to stand and set. The mold was held together by ½-in. bolts. It would have been more practical to have had the side casting composed of two parts.
The form for the railing is built up around the tops of the spindles. The bottom piece is 1×9 ins., to which 4¼-in. ogee molding is nailed. The sides are of 1-in. stock, and are clamped together. The top is finished off with a trowel.
The mold for the posts is made in four parts, which fit together at the top and bottom by a bevel joint, as shown in the one-fourth section. The broad sides rest against the narrow ones, and are held against the same by means of ½-in. rods running through 2×3-in. stock: 2-in. projections of the broad sides facilitate the removal of the form from the completed post.
