32 MOLDING CONCRETE CHIMNEYS together; these are fastened to one section of mold and hold the next section by a bolt through a slot in the strap-iron. This slot is 21" in length, in each one, thus permitting the outside circumference of mold to be decreased 20" by drawing the sections together. The molding surface of centering is made up of sheet steel-plates, 26 or 27 gauge. These are cut so as to just fit or lap over onto the next plate upon each side, when the form is extended to its greatest circumference. These plates are fastened with screws to each section of the mold. Thus when the sections are drawn together, the steel-plates lap on to those upon each side, and take up the surplus centering without disturbing the perfect circle. As the inside diameter of the chimney is usually the same for the entire height, the core form can be built with the sections fastened rigidly together; but where it is desired to increase or decrease the diameter of same as the forms are raised, the strapiron strips used to fasten the sections together can be employed in the same manner as for the outside form. In the illustration at Fig. 7, the strap-iron fastenings to each section are shown at g g; the concave or outside sections are designated by ff; the convex or core sections are shown at e e. The vertical posts in center, used to raise the forms, are designated by a a, while the guide-strips employed upon side of center posts to insure the forms being raised accurately are indicated at c c. The strip b b, extends entirely across the form and is attached to both the core and the outside sections of centering; this is placed between the two vertical posts in center, and is used to raise the forms as the work progresses. The braces shown by the dotted lines at d d are used to keep the sections to the true circle. This is more perfectly illustrated in Fig. 8, which shows a sectional view of the forms, and the vertical upright employed to raise same, as each course of concrete is placed. The position of the outside and inside sections and the arrangement of the supporting strip b b, are clearly shown, as well as the advantages secured in employing the short guide-strips at each side of the vertical posts. As the forms are raised by the rope tackle, these strips prevent one side of the forms from being raised higher than those upon the opposite side, thus insuring that the forms will always be level. The vertical posts are securely braced at the bottom, and must be amply strong for the work. As the chimney is constructed, other sections of these center posts are attached to the top of those in position, thus enabling the work to be carried to the height desired. This is accomplished by bolting the posts together at the top, with a block between same, that will hold them far enough apart so the guidestrips bb will slide easily. When the forms have been raised to the top of the posts, a bolt and block are placed below the lower cross-strip, and the bolt and block at top of posts removed. The second section of posts is then attached to the top of those erected; and, when these are securely stayed with guy ropes or wires with the tackle fastened at top of same, the forms are again raised to the height of this section, and again in the same manner until the work is finished. The forms at no time are dependent upon the walls of chimney for support, thus avoiding the chances of an accident by raising the forms too quickly. The vertical posts in center must be carefully selected, and be amply able to carry the forms as well as the weight of the center posts added to same. The position of the rope tackle employed to raise the forms is shown by the dotted lines in Fig. 8, although this may be changed to any method of raising the forms that the worker may desire. The batter to the walls is secured by adjusting the bottom of sections to fit the top of wall just molded, and adjusting the top sections of centering so the circumference is decreased the proper distance. This is arranged by estimating the number of times the forms must be raised to secure the height desired, then dividing the 2" slot in strapiron into spaces to conform to the number of adjustments demanded. AN OCTAGONAL MONOLITHIC FORM At Fig. 9 is shown a method of arranging strips to form an octagonal or circular, as may be desired, |