The first thing in the practice is to spring the plank, then to cut away the superfluous wood, as directed by the draughts formed by the fitee-mould. This may be cut so very exactly with a saw, by an experienced hand, as to require no further reduction ; and N% hen set in its place, the suifice on both sides will be vertical in all parts, and in a sin thee perpendicula• to the plan. In order to form the hack and lower surface, the falling-mould is applied to one side, which is generally the convex side, in such a manner, that the upper edge of the thlling-mould at one end may coincide with the face of the plank, the same in the middle, and to leave so much wood at the other end to be taken away, a,% not to reduce the plank on the Concave side. The piece of wood to be thus 'brined into the w reath or twist, being agreeable to three given heights. This description i_s general, in order to elm] prebend the follow ing construction of the moulds themselves, which when explained, we shall then enter into a inure particular detail of their application.
To construct the filling and jiice-moulds of a rail to a level landing, supposing the plane of the plank to rest upon the middle point of the section, which separates the upper and lower circular parts, and to rest upon the line parallel to, and in the middle of the straight part, so as to have the grain the wood parallel.
Plate I. Figure I.—The falling-mould of the hand-rail : n c the extension of the semicircular part ; 13 A and e n the treads of the adjoining flyers.
To find the extension of the semicircular part, from the middle point, 1, of a c, draw 1 K L perpendicular to ; divide the radius 1 x into four equal pacts, and repeat one of these parts from s to L seven times ; draw the diameter at N parallel to e; join a If and t. N, and produce each of these lines to 13 and c ; then B C is the rectification of the semi-eircumferenee • I N. Draw a T and o n perpendicular to A a; make B E equal to the height of a step ; t o on the straight line 1 L, one step and a half; c F equal to the height of two steps ; and v in equal to the height of three steps ; join A E and it F, and through o draw a o parallel to u e ; produce A E and tr F to meet r Q at a and u ; then cut on' the angles at a and o by equal touching curves, one at each ; then A E o F IS the middle of the fidling-mould ; and as the rail is generally made two inches deep, draw two parallel lines each an inch distant from this central line, and s u will be the upper edge of the fidling-mould, and d v J the lower edge.
Tu find the lace-mould of the handrail.
Figure 2.—At any convenient place lay down the half plan, bedefa, of the 1i:111d-rail ; (IGO' being the straight part of the rail, and c d eftlie plan of the circular part; draw g e d parallel to a f or b c; bisect d e at b, and draw h i perpen dicular to g d ; make /t i equal tot u, Figure 1, and the angle h i k equal to the angle o rt F ; let b. represent the middle
point of the section between the two circular parts ; and suppose a to represent the resting point in the middle of the section, which separates the straight and circular loarts ; make in a., _Figure 1, equal to c b or f a, Figure 2, and draw it s, Figure perpendicular to A B, cutting the upper edge of the falfing at s ; make h r, Figure 2, coin's! to n T, Figure and draw r s, Figure 2, parallel to y d, cutting i k at s; make It in equal to rs, and join in a, which is the directing ordinate ; from k draw k 1 parallel to in n, and A.1 is the intersection of the plane of the plank ; find the countersection as in the SEe•oss OF CvLINDEas, or as in the subsequent part of this Work, under Soul, ANGLES.
To find any point in the curve of the facc-mould.—Draw ear iv parallel to A' 1, cutting k d at a, and this concave side of Ale plan at a, and the convex side at no; draw u x parallel to b cutting i at x; draw x y z parallel to k ; make. y equal to and .r z equal to a w; then y is a point in the concave side of the face-mould, and z is a point in the convex side. The pitch-bevel shown by the darns lines, is found by drawing a vertical line to the pitch-line,and the angle formed by these lines is the pitch-bevel.
In this manner as many points may be found as will be neeessa•y to complete the concave and convex sides of the falling-mould ; or rule each system of lines at the same line, thus; take as many points in the convex side of the plan as will be found requisite ; through all these points draw lines parallel to A- to ent g 1.1 ; from all the points of division in y d draw lines parallel to h i, cutting k i; through all the points of division in A. I draw lines parallel to A. ; terminate each line from the point of intersection equal to the corres ponding outer and inner (ordinates of the plan, and through the points found by its concave side draw a line ; also through the points found by the convex side of the plan draw another curve : then the points found for each ext•emity of the plan will complete the It is evident that the parts 3•4, 5-6 of the face-mould corres ponding to a b, (ion the plan, is a parallelogram, therefore if the point 6, where the concave side and the straight parts meet, and the point 5, where the convex and straight parts meet, are found and joined by the line 5-6 ; and if 5-4 and 6-3 be drawn parallel to i, and the point /-/ corresponding to o, be found. by drawing- through 9., the straight part of the face-mould will be completed.