This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Sometimes it is necessary to build a structure with the walls inclined inward, so that they approach each other at the top, and so that the top is smaller than the bottom. This is the case with the frames which support water tanks or windmills. An elevation of one side of a frame of this kind is shown in Fig. 211 with a plan in outline at C. It will be seen that the corner posts A A are inclined so as to approach each other at the top, and that they are not perpendicular to the sill at the bottom. This means that the foot of the post, where it is tenoned into the sill, must be cut on a bevel, and the bevel must be cut diagonally across the post, from corner to corner, since the post pitches diagonally toward the center, and is set so that its outside faces coincide approximately with the planes of the sides of the structure as indicated in the plan shown in Fig. 212. The girts B, Fig. 211, will also have to have special bevels cut at their ends, where they are framed into the posts.
Fig. 211. Battered Frame.
After a corner post has been cut to the proper bevel to fit against the sill the section cut out at the foot will be diamond shaped, as shown at A B C D in Fig. 212, which shows a plan of one corner of the sill. It will be noticed that the faces A B and A D of the post do not coincide with the edges of the sill A F and A G. If the structure is merely a frame and is not to be covered over with the boarding on the outside, it is not necessary that the outside faces of the post should coincide exactly with the planes of the sides of the structure, and in this case posts of square or rectangular section may be used, with no framing except the bevels and the mortises for the girts. If, however, the frame is to be covered in, the post must be backed in order that it may be prepared to receive the boarding.
Fig. 212. Battered Frame Detail.
The backing consists in cutting the post to such a shape that when the bevel is cut at the foot, the section cut out will be similar to that shown at E B C D in Fig. 212. The backed post must then be set on the sills so that the point E will come at the corner A. The face of the post E B will then coincide with the face of the sill A F. The post should be backed before the top bevel is cut because setting it back the distance A E may make a difference in the required length between bevels. If the post is of square section before backing it will have, after backing, a peculiar rhombus-shaped section, as is shown at A in Fig. 212. Here H I J K shows the original square section, and L I J K shows the section after backing. These sections are taken square across the post perpendicular to the edges.
Fig. 213 shows how the foot cut for the inclined post may be obtained by using the steel square. In Fig. 211 it will be seen that the post A slopes toward the center in the elevation there shown, and it likewise slopes toward the center in the other elevations, either with the same pitch or with a different pitch. The result of the two slopes is to cause the post to slope diagonally. It is an easy matter to find the pitch in each elevation since it depends upon the size of the base and top, and the height between them. We then have the two pitches, the combination of which gives the true pitch diagonally; they can, however, be treated separately. The square may be applied to the post, as shown in Fig. 213, with the rise on the blade and the run on the tongue, and a line may be drawn along the tongue. The post can then be turned over and the pitch shown in the other elevation may be laid off on the adjacent side in the same way, with the rise on the blade and the run on the tongue of the square. Thus a continuous line A B C D may be drawn around the post and it can be cut to this line.
Fig. 214. Method of Finding Amount of Backing for Post.
Fig. 214 shows how the amount of backing necessary in any particular case may be determined. Suppose that we have a case where the plan of the frame is not square, as shown in Fig. 211, but is rectangular, one side being much longer than the other. In this case the diagonal of the frame formed by the sills will not coincide with the diagonal section of the post. Fig. 214 shows at A a plan of the post as it would appear if it were set up with one edge perpendicular to the sill M, after the bottom bevel is cut. To cut the backing, lay the steel square along the side of the post parallel to M, and so as to coincide with the opposite corner 0. When the triangular piece R S O is cut away, the backing is complete. At B is a plan where the post is set with corners T T, so as to coincide with the outside edges of the plate. To back the post in this position, place the square so as to coincide with the points T T, making the distance C T and C T proportional to the lengths of the sills M and. N. In this case, the backing consists in cutting away the area S T C T.