15. In geometrical stairways, the hand rail travels, unobstructed by newels, from the first step to the last, sometimes over six or more flights; it then becomes necessary to wreath the stringer and rail around the well holes. The well holes thus treated are said to contain a cylinder. In stair building, any form of a curve constitutes a cylinder when used for this purpose. In a circular stairway, the cylinder assumed has a complete circumference of a circle for its plan, and the stringer and rail are made to wind around it, following a curve termed a helix - a curve of the same nature as the winding thread of an ordinary screw. The finished treatment of the stringer and balustrade is continued around the cylinder, and where the stairway terminates in a landing, the same treatment is continued along the trimmer beam. The portion on the beam corresponding to the stringer is called the facia. Thus it will be seen that the stringer of the flights, the cylinder of the well hole, and the facia of the trimmer beam arc but parts of one continued stringer known by different terms.

Cylinders are built up as shown in Fig. 14. The construction shown at (a) is used for small cylinders, while for larger ones, the methods shown at (b) and (c) are used. The joints, as s t and v s, are glued and strengthened by screws or wooden dowel-pins. For extra fine work the face of the cylinder is veneered, so that the joints of the staves in the semicircle from a to b, in (c), are covered. The veneer is bent over a skeleton cylinder whose diameter is equal to the diameter of the well cylinder, and then backed with properly fitted staves, as c and d, well glued, and screwed or doweled at the joints, if necessary.

The end staves of small cylinders are fastened to the stringers in various ways. Two common methods are shown in Fig. 15. In the first method (a), a dovetailed groove is cut in the stringer into which the end stave fits. Wedges W, glued in, hold the stave in place, In the second method (b), the end staves are merely set into the stringers and screwed fast from the outside.

(a)

(b)

Fig. 14.

Fig. 15.