In [Fig. 125] is shown a case where the risers are placed at a distance from c equal to a full tread, the effect in respect to the tangents of the face-mould and bevel being the same as in the two preceding examples. In [Fig. 126] is shown the plan of [Fig. 123]; in [Fig. 127], the plan of [Fig. 124]; and in [Fig. 128], the plan of [Fig. 125]. For the wreaths shown in all these figures, there will be no necessity of springing the plank, which is a term used in handrailing to denote the twisting of the wreath; and no other bevel than the one at the upper end of the pitch-board will be required. This type of wreath, also, is the one that is required at the top of a landing when the rail of the flight intersects with a level-landing rail.
In [Fig. 129] is shown a very simple method of drawing the face-mould for this wreath from the pitch-board. Make a c equal to the radius of the plan central line of rail as shown at the curve in [Fig. 130]. From where line c c″ cuts the long side of the pitch-board, the line c″ a″ is drawn at right angles to the long edge, and is made equal to the length of the plan tangent a c, [Fig. 130]. The curve is drawn by means of pins and string or a trammel.
In [Fig. 131] is shown a quarter-turn between two flights. The correct method of placing the risers in and around the curve, is to put the last one in the first flight and the first one in the second flight one-half a step from the intersection of the crown tangents. By this arrangement, as shown in [Fig. 132], the pitch-line of the tangents will equal the pitch of the connecting flight, thus securing the second easiest condition of tangents for the face-mould—namely, as shown, two equal tangents. For this wreath, only one bevel will be needed, and it is made up of the radius of the plan central line of the rail o c, [Fig. 131], for base, and the line 1-2, [Fig. 132], for altitude, as shown in [Fig. 133].
The bevel shown in this figure has been previously explained in [Figs. 105] and [106]. It is to be applied to both ends of the wreath.
The example shown in [Fig. 134] is of a well-hole having a riser in the center. If the radius of the plan central line of rail is made equal to one-half a tread, the pitch of tangents will be the same as of the flights adjoining, thus securing two equal tangents for the two sections of wreath. In this figure the tangents of the face-mould are developed, and also the central line of the rail, as shown over and above each quadrant and upon the pitch-line of tangents.
The same method may be employed in stairways having obtuse-angle and acute-angle plans, as shown in [Fig. 135], in which two flights are placed at an obtuse angle to each other. If the risers shown at a and a are placed one-half a tread from c, this will produce in the elevation a pitch-line over the tangents equal to that over the flights adjoining, as shown in [Fig. 136], in which also is shown the face-mould for the wreath that will span over the curve from one flight to another.
In [Fig. 137] is shown a flight having the same curve at a landing. The same arrangement is adhered to respecting the placing of the risers, as shown at a and a. In [Fig. 138] is shown how to develop the face-moulds.
FINISHED ROOF TRUSS IN FIRST PRESBYTERIAN CHURCH, SYRACUSE, N. Y.
Tracy & Swartwout, Architects; Ballantyne & Evans, Associated.
Reproduced by courtesy of “The Architectural Review.”