The face-mould, as here presented, will further help toward an under standing of the lay out of face-moulds as shown in Figs. 96 and 97. It will be observed that the pitch of the bottom rail is con tinued from a" to b", a condition caused by the necessity of jointing the wreath to the end of the straight rail at a", the joint being made square to both the straight rail and the bottom tangent a". From 5" a line is drawn to d", which is a fixed point determined by the number of risers in the well-hole. From point d", the level tangent d" 5 is drawn in line with the level rail of the landing; thus the pitch-line of the tangents over the well-hole is found, and, as was shown in the explanation of Fig. 95, the tangents as here presented will be those required on the face-mould to square the joints of the wreath.
In Fig. OS the tangents of the face-mould for the bottom -wreath are shown to be a" and 5". To place tangent a" in position on the face-mould, it is revolved, as shown by the arc, to m, cutting a line previously drawn from w square to the tangent b" extended. Then, by connecting m to b", the bottom tangent is placed in position on the face-mould. The joint at m is to be made square to it; and the joint at c, the other end of the mould, is to be made square to the tangent b".
The upper piece of wreath in this example is shown to have tangent c" inclining, the inclination being the same as that of the upper tangent b" of the bottom wreath, so that the joint at c", when made square to both tangents, will butt square when put together.
The tangent d" is shown to be level, so that the joint at 5, when squared with it, will butt squareiwith the square end of the level-landing rail. The level tangent is shown revolved to its position on the face-mould, as frorri 5 to 2. In this last position, it will be observed that its angle with the inclined tangent c" is a right angle; and it should be remembered that in every similar case where one tangent inclines and one is level over a square-angle plan tangent, the angle between the two tangents will be a right angle on the face-mould.
A knowledge of this principle will en able the student to draw the mould for this wreath, as shown in Fig. 99, by merely drawing two lines perpen dicular to each other, as d" 5 and d" c", equal respectively to the level tangent d" 5 and the inclined tangent c" in Fig.
98. The joint at 5 is to be made square to d" 5; and that at c", to d" c".
Comparing this figure with the face mould as shown for the upper wreath in Fig. 98, it will be observed
that both are alike.
In practical work the stair-builder is often called upon to deal with cases in which the conditions of tangents differ from all the examples thus far given. An instance of this sort is shown in Fig. 100, in which the angles between the tangents on the plan are acute.
In all the preceding examples, the gents on the plan were at right angles; that is, they were square to one another.
Fig. 100 is a plan of a few curved steps placed' at the bottom of a stairway with a curved stringer,which is struck from a center o. The plan tangents a awl b are shown to form an acute angle with each other. The rail above a plan of this design is usually ramped at the bottom end, where it intersects the newel post, and, when so treated, the bottom tangent a will have to be level.
In Fig. 101 is shown how to find the angle be tween the tangents on the face-mould that gives them the correct direction for squaring the joints of the wreath when it is determined to have it ramped. This figure must be drawn full size. Usually an ordinary drawing-board will answer the purpose. Upon the board, reproduce the plan of the tangents and curve of the center line of rail as shown in Fig.100. Measure the height of 5 risers, as shown in Fig. 101, from the floor line to 5; and draw the pitch of the flight adjoining the wreath, from 5 to the floor line. From the newel, draw the dotted line to w, square to the floor line; from w, draw the line w m, square to the pitch-line IA Now take the length of the bottom level tangent on a trammel, or on dividers if large enough, and extend it from to nt, cutting the line drawn previously from w, at 711. Connect in to n as shown by the line a". The intersection of this line with b" determines the angle between the two tangents a" and b" of the face-mould, which gives them the correct direction as required on the face-mould for squaring the joints. The joint at M is made square to tangent a"; and the joint at 5, to tangent In Fig. 102 is presented an example of a few steps at the bottom of a stairway in which the tangents of the plan form an obtuse angle with each other. The curve of the central line of the rail in this case will be less than a quadrant, and, as shown, is struck from the center o, the curve covering the three first steps from the newel to the springing.