Suppose Stair Parts Fig. 23 to be the ground plan of cylinder, with risers placed in a position that insures an easy, graceful rail, and also adds to the run by curving the landing and starting risers back to the platform.
Stair Parts Fig. 23
To construct Stair Parts Fig. 23, draw the center line of rail and tangents ABCD; from B and C as centers, swing around A and D, cutting B and C extended; swing around the risers E and F in like manner; place pitchboard with riser parallel to AB and touching H, and the raking side, cutting through G. Mark out the treads and risers as shown at XXXX. Draw pitchlines, as shown, cutting AB and DC extended up; join IK, and the pitch-line is complete. To obtain the angle of tangents at K draw dotted line from center of cylinder cutting IX at L. Draw MN through L parallel with BC. At right angles to upper pitch-line draw dotted line NO. From center K swing around KL to O; connect KO, and the angle is complete.
To obtain the spring bevels - from center B describe an arc, touching the pitch-line KI extended, and cutting BI at P; connect PG, and the bevel for center joint is found at P.
To obtain bevels for joints connecting with straight rail, take M as a center and describe an arc touching lower pitch extended connect with L, and the bevel is found.
Stair Parts Fig. 24 and 25
Stair Parts Figs. 24 and 25 show the sections and application of bevels on rails. Stair Parts Fig. 24 is the lower and Stair Parts Fig. 25 the upper wreath; the same face would serve for both, as the upper and lower pitches are the same.
Let us now examine Stair Parts Figs. 3 and 4, and endeavor to form rails to suit them. As before stated, these two examples represent on the ground plans obtuse and acute angles at the return landings; and in the formation of rails to meet the requirements for these stairs, the student will have covered the ground for the formation of rails for nearly every kind of rail required for a platform stair. In locating these risers at the landings be sure to place them, if possible, exactly half a step each way from angle B, Stair Parts Fig. 26. This will insure an easy rail.
Stair Parts Fig. 26
Stair Parts Fig. 26 shows the development of the angle of tangents for the face mould and the bevel for springing the wreath. Draw the angle ABC on center line of rail as shown; draw dotted line from center O to B; draw DE at right angles to OB; from center B swing around A and C to D and E; set up one riser from D, to F, and one down from E; mark one step above and below the pitch-board; draw pitch-line XX.
Connect CA, and continue OB to G; with B as a center, describe an arc touching CA; from G as a center with the same radius, describe an arc; from E draw line touching this arc; from G again swing around GF to H; connect GH, and d the angle of tangent is complete. The amount of straight wood on wreath is shown from E and H to the joints XX.
Stair Parts Fig. 27
To obtain the bevel it is first necessary to find the point I; from H with FD for radius, swing an arc and intersect with another from E; having CA for radius, connect El and HI; take a center, K, anywhere on the line EH, draw an arc touching GH and cutting EH at L; square down from K, cutting JH at M; connect LM, and the bevel is found for both joints of the wreath, the pitch being one straight line. Stair Parts Fig. 27 shows application of bevel to wreath.
Stair Parts Fig. 28
Stair Parts Fig. 29-30
Stair Parts Figs. 28 and 29 are simply a repetition of Stair Parts Figs. 26 and 27 excepting that the ground plan forms an obtuse angle. Fig. 30 shows the manner of sliding the mould on the wreath to mark it for blocking. We may state here that there have been worked some hundreds of rails during the past thirty years by this method, and we have come to the conclusion that the easiest and quickest way to block out a rail is to use just such moulds as are shown in the drawing, viz., of a parallel width, and just sufficiently large to square the rail properly for moulding. When the wreath is sawed out, the face of stuff carefully planed true, the tangents marked and the joints made perfectly square with the face and with the tangents, then square the tangent across the joints, mark the center and draw the bevel across, as shown in Stair Parts Fig. 27, mark the section of rail at right angles to bevel. The best method of doing this is to use a thin templet with a small hole in the center, through which put a, scratch awl, them swing the templet until exactly at right angles with bevel And mark all round it. The section being marked, square in from the joints on all sides to mike` sate the wreath will bolt on to the straight rail form a clean line. To mark the curve line Allae the mould up, as shown in Fig. 36, mark the Inside edge (this line will not be quite as accurate as one made from an elliptical mould on the sliding principle with wide ends, but it is near enough for all practical purposes) by roughing but the inside first and occasionally planing through the wreath. Looking in the direction of a plumb-line, it will be, seen at once when to take off the superfluous wood, and with a little care the inside will soon show a clean, true surface. As soon as this is done gauge the wreath to a width, then bend in a thin strip. Connecting the straight lines squared in from each end, mark around the outside in the same manner, mark off the top, gauge to a thickness, and the wreath is squared. The plumb-line can be marked on the inside of the wreath, and will give the line of sight by taking the bevel from the angle EHJ, Stair Parts Fig. 26.