Fig. 103. Developing Face-Mould, Obtuse-Angle Plan.
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 square with the square end of the level-landing rail. The level tangent is shown revolved to its position on the face-mould, as from 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 enable the student to draw the mould for this wreath, as shown in [Fig. 99], by merely drawing two lines perpendicular 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 tangents on the plan were at right angles; that is, they were square to one another.
Fig. 104. Cutting Wreath from Plank.
Fig. 105. Wreath Twisted, Ready to be Moulded.