In drawing ordinates upon the plan, care should be taken that an ordinate be drawn through the points upon each side of the plan at the line of separation of the straight and circular parts, and also through each extremity of the ends; or, by finding m N. the line of' separation, and the point K, the point a will be Ibund by drawing K L parallel to N and zr L parallel to N s; and thus the portion N K I, corresponding to vxku on the plan, will be obtained.
The angle p o in gives the spring-bevel, Figure 2, No, 3; and the angle s r q gives the pitch-bevel, Figure 2, No. 2. The lace-mould is applied to the plank by laying the points r and K close to the edge that is sprung ; then drawing the pitch-bevel, No. 2, from either point P or s; for it is not necessary to draw them from both, as the corresponding point ;Nil] be found upon the other side of the plank ; then proceed with the remaining parts as bethre directed.
To spring the plank for a level landing through two given points, so us to parallel the grain.
Plate 111.—Let No. 3 be the fidling-mould, as before: draw any line, c A, for the base of the heights of the thee mould ; then c D is the lower height, where the two wreathed pieces meet, and A a is the upper height, making allowance for the squaring of the joint. Lay down the plan A k c, No. I ; draw c n parallel to A k; draw A B perpendicular to A k; make A B equal to A B. No, 3, and the angle A B E, No. 1, equal to the angle v w s, No. 3; produce A k to E; draw c D par allel to A B ; make c n to c D, No. 3, and the angle c n F equal to the angle A B E, that is, equal to the angle v w s, No. 3: produce a C to F; join F E; in F E take any point, E, and draw E i perpendicular to F c, meeting it in I; from I draw I K perpendicular to F G, cutting it in a ; make r a equal to I a, and join H E; make LK equal to H E, and join F K; then F E is the director of the ordinates of the base, and F that of the thee-mould. Proceed with the rest as in Plate 1. Figure 1.
No.2 shows the other mould ; but it must be observed, that one mould is sufficient for both wreaths.
Plate IV. shows the falling and face-moulds of a rail with winders. As to the method of laying down the moulds from three given heights, the principle is the sante as described in Plate]. for a level landing, It therefore only remains to
speak of the manner of forming the butt-joints. Draw a line at right angles to the sides of the falling-mould, through the middle of the vertical line, where otherwise would have been the splice joint; front the end of this line draw another at the upper edge, and also one from the under edge, perpendicular to the base line ; then the middle height being taken as usual, the remote line is the height of the face-mould.
Thus, n I, No. 1, is the height of h i, No. 2; a, No. 1, the height of k 1, No. 2; and at x, No. 1, the height of in n, No. 2; the remaining part of the construction is as usual. No. 3 is the upper thce-mould, taken from inverted heights: or the falling-mould may be considered as inverted. The same letters are put upon both constructions, to show the similar parts. Here are eight winders, all drawn to a scale, to show the proportion of the parts in practice. This hand rail requires two moulds, on account of' the middle of the falling-mould being much higher than the hypothenuse of the ers.
Plate V. shows the falling and face-moulds for a rail con structed as in Plate IV. The only difference is, that in this Plate the middle of the falling-mould is the hypothenuse of the wreath. This situation of the falling-moulds will cause both the face.moulds to be identical : that is, their figures will be equal and shnilar, so that considerable time will be saved in the preparation. This position, and the identifica tion of the moulds, Dilly always be adopted when the distance between the opposite parts of the string is more than ten inches. The mode of making the height of the rail in the middle of the w inders the same as that of the flyers, is prac tised by several celebrated staircase hands, though it is nothing more than a mere matter of opinion, and may be adopted or not, at the option of the architect, or of the workman, if left to him.
It is worthy of notice, that the springing of the plank is of the utmost consequence in the saving of stuff. where the well-hole is wide; but where it is narrow, very little will be gained by it.