Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/540

482 BUILDING [CARPENTRY. arches. always cut in with the saw ; but the cheek is for the most part struck out with the mallet and chisel, or adze, as may be most convenient. Tenons should be made entirely with the saw. Mortises are generally bored at the ends with an auger whose diameter equals their thickness ; the inter vening part is taken out with a wide chisel, cutting in the direction of the fibre ; and the ends are squared down with a chisel whose breadth just equals the thickness of the mortise. Wood pins must be rent to insure the equal tenacity of their whole mass. Wedges are cut with the saw, but straight-grained stuff is always preferred for them. Bond-timbers and wall-plates should be carefully notched together at every angle and return, and scarfed at every longitudinal joint. The scarf shown at fig. 1, Plate XXIV., is sufficient ; and the notch at No. 3, fig. 2, may be preferred where notching is required ; neither pinning nor nailing, however, can be of great use to either the notch or the scarf. Bond-timbers are passed along and through all openings, and are not cut out until such openings are to be permanently occupied, that is, by windows with their sash-frames, &c., because they assist in preventing irregular settlements, by helping to carry the weight of a heavy part along the substruction generally, instead of allowing it to press unduly upon the part immediately under it. It is the duty of the carpenter to supply the bricklayer or mason with wood bricks in sufficient quantity, arid to direct him where they should be placed to receive the joiner s fittings, or the battening, which the carpenter himself may have to put up for the plasterer. Centres for The carpenter makes and fixes or sets centres of all kinds, whether for single arches or niches, or even in bridge construction. Large centres are framed in distinct ribs, and are connected by horizontal ties ; whilst small ones are made of mere boards cut to the required sweep, nailed together, and connected by battens notched into or nailed on their edges. Precision and stability are nevertheless equally and absolutely necessary, as it is impossible for an arch to be turned or set correctly on an incorrect or unstable centre. Floors. Descriptions of various sorts of flooring are noticed in the earlier part of this article as for fireproof structures ; and also under Brickwork and Mason-work. The timbers or framework of ordinary house and warehouse floors is called naked flooring, and it is distinguished as single, double, and framed. Of these the first, under ordinary circum stances, is the strongest. Single Single flooring (Plate XXV. figs. 1, 2) consists of one row flooring. or ^[ er O f j i s t s alone, bearing from one wall or partition to another, without any intermediate support, and receiving the flooring boards on the upper surface or edges of the joists, and the ceiling, if there be one, on the lower. Joists in single floors should never be less than 2 inches in thickness, because of their liability to be split by the brads or nails of the boards if they are thinner ; and they should never be much more, because of the keying of the ceiling, which is injuriously affected by great thickness of the joists. Twelve inches from joist to joist is the distance generally allowed ; that dimen sion, however, from centre to centre of the joists would be bet ter Strength to almost any extent may be given by adding to the depth of the joists, and diminishing the distance be tween them ; and they may be made firm, and be prevented from buckling or tvisting, by putting struts between them. The struts are short pieces of batten, fig. 31, which should not be less than an inch, and need not be more than an inch and a half thick, and 3 or 4 inches wide, placed diagonally between the joists, to which they are nailed, in a double series, or crossing, as indicated by ,-, , the full and dotted lines in Plate XXIV. fig. 7 ; and they should be made to range in a right line, that none of their effect may be lost ; and these ranges Fio. 32. Herring bone Strutting. or rows should be repeated at intervals not exceeding 5 or G feet. The struts should be cut at the ends with exactly the same inclination or bevel, to fit closely. Great care should be taken, too, not to split the struts iu nailing ; but the trouble of boring with a gimlet is saved by making a slight nick or incision with a wide-set saw for each nail, of which there should not be less than two at each end ; and the nails used should be clasp-nails. If the struts were notched into the joists, as in fig. 32, it would add very materially to their efficiency, but perhaps not in proportion to the additional labour it would involve. This strutting should be done to single floor ing under any circumstances, as it adds materially to its firmness and indeed to its strength, by making the joists trans mit any stress or pressure from one to another. The efficiency of single flooring is materially affected by THmm the necessity which constantly occurs in practice of trimming round fire-places and flues, and across vacuities. Trimming is a mode of supporting the end of a joist by tenoning it into a piece of timber crossing it, and called a trimmer, instead of running it on or into the wall which supports the ends of the other joists generally. A trimmer requires for the most part to be carried or supported at one or both of its ends by some of the joists, which are called trimming joists, and are necessarily made stouter than if they had to bear no more than their own share of the stress. Commonly it is found enough to make the trim mers and trimming joists from half an inch to an inch thicker than common joists. In trimming, tusk tenons should be used ; and the long tongue or main body of the tenon should run not less than 2 inches through, and be draw-pinned and wedged, moreover, if it do not completely fill the mortise in the direction of the length of the latter. The principal objection, however, to single flooring is, Object: that sound readily passes through, the attachment of the to sing boards above and of the ceiling below being to the same lloors> joists throughout. Another objection, and one already referred to, is the necessity of making the joists so thin, not to injure the ceilings, that they with difficulty receive the flooring brads in their upper edges without splitting. A partial remedy for both these disadvantages is found in a mode sometimes adopted of making every third or fourth joist an inch or an inch and a half deeper than the inter vening joists ; and to these, ceiling joists are notched and nailed, or nailed alone, as shown in Plate XXIV. fig. 7. This, by diminishing the number of points of contact be tween the upper and the lower surface, for the ceiling joists must be carefully kept from touching the shallower joists of the floor, is less apt to convey sound from one story to another, and allows conveniently thin joists to be used for the ceiling without affecting those of the floor. Double flooring (see Plate XXIV. fig. 8, Nos. 1 and 2, Doubl and Plate XXV. fig. 3) consists of three distinct series of flooriri joists, which are called binding, bridging, and ceiling joists. The binders in this are the real support of the floor ; they run from wall to wall, and carry the bridging joists above and the ceiling joists below them. Binders need not be less and should not be much more than 6 feet apart, that is, if the bridging or flooring joists are not inordinately weak. The bridging joists form the upper tier, and are notched down on the binders with the notch No. 5, Plate XXIV. fig. 2. The ceiling joists range under the binders, and are notched and nailed as shown at No. 1, fig. 8 ; but the notch must be taken entirely out of the ceiling joists, for. the lower face or edge of the binder may not be wounded by any means or on any account, and, moreover, no good

would be gained in any other respect by doing so. When