SECT. IV. CARPENTRY. 2003. Carpentry is the science of framing or letting into each other an assemblage of pieces of timber, as are those of a roof, floor, centre, &c. It is distinguished from joinery in being effected solely by the use of the are, the adze, the saw, and the chisel, which are the carpenter's tools; whereas joinery requires the use of the plane. See 2102, et seq. 2004. Though necessarily of high antiquity, the very scanty information which Pliny and Vitruvius have left us on the subject would merely show that the science was known by the ancients. The roofs of Egypt present us with no more than flat coverings of massy stone; a pediment roof, therefore, would seem to have been among the first efforts of constructive carpentry; and upon the pitch which this, then and since, has received in different countries, we shall hereafter have to speak. The Greeks appear to have used carpentry in the construction of their floors and some other purposes; but in a country abounding with stone and marble, it is not likely that wood was much used in the interiors of their buildings, unless where lightness, as in doors, for instance, required its employment. With the Romans it was much more commonly used; and from all that can be gathered, we may consider them as the fathers of the science. 2005. Among the moderns it has been very successfully cultivated; and, with very few exceptions, we may almost assert that the works of Palladio, Serlio, De Lorme, Sir Christopher Wren, Perronet, and a few others, exhibit specimens which have scarcely been surpassed in later times, notwithstanding the scientific form it has assumed in the present age. 2006. To the mechanical principles of carpentry we have, in Chap. I. Sect X. of this book, directed the attention of the student; and to the section now under our pen we should have added the words Descriptive and Practical to Carpentry, but that much of what could have been said on that head has already been anticipated in the section on Descriptive Geometry. Hence, in what follows, that which comes under such pred cament will be only given in particular cases, for the purpose of saving time and trouble to the reader in the application of its principles to them. We must, here, also remind the reader, that under the section BEAMS, &c., and TIMBER, have been described the different sorts of timber used for building purposes, their strengths, and the strains to which they are subject and which they are capable of resisting; and that therefore this section is confined simply to putting pieces of timber together, so as to form the assemblage of timbers under which we have commenced by defining the science. To do that properly requires great skill and much thought. Considerable waste, and consequent expense to the architect's employer, result from that ignorance which assigns to the scantlings of timber larger dimensions than are absolutely necessary for the office of each piece; insufficient scantlings will bring the architect into trouble and responsibility; and the improper connection of the pieces will be equally ruinous to his reputation. The principles of practical carpentry are, nevertheless, simple; and though to form new combinations and hazard bold and untried experiments in practice will require all the skill and science of a talented artist, the ordinary routine of carpentering is to be learnt by a little application and a due exercise of common sense. 2007. After these observations, we must introduce the student to the first operation which in practice may arise. It is not every where that timber can be obtained in sufficient lengths to stretch across the void he has to cover; and it will in such cases be necessary for him to know how one piece of timber may be so joined to another, for the purpose of lengthening it, that the two pieces, when joined, may be as nearly as possible equal in strength to one whole piece of timber of the same dimensions and length. This operation is of great service to the builder, and is technically called scarfing. To perform it, the joints are indented, and bolts are passed through the pieces within the length of the indents, such bolts being confined above and below by means of nuts and screws. In fig. 653. four ways are exhibited of accomplishing the object in question. A and B are the methods usually employed for joining together plates, lintels, and ties, in which bolts Fig. 665. B are rarely necessary; but if such a method is used for scarfing beams, bolts must be employed. The stronger forms, which only should be used for beams, shown in C and D, are not only in that respect such as should, on that account, be used for beams, but are executed without loss of length in the pieces of timber. The length of the joints of the scarfing may be increased at pleasure; the diagrams are merely given to show the mode of doing what was required. With fir, however, when bolts are used, about four times the depth of the timber is a usual length for a scarf. Scarfing requires great accuracy in execution; for if the indents do not bear equally, the greater part of the strength will be lost: hence it is improper to use very complicated forms for the indents. 2008. Pieces of timber are framed into and joined to one another, by the aid of mortices and tenons, and by iron straps and bolts; and on the proper placing of these depends the soundness of the work. If a piece of framing is to stand perpendicularly, as in the case of partitions, without pressure from either side, the mortice and tenon should be in the centre of the wood. But in the case of framing floors, in which the pressure is on the upper surface, and entirely on one side, the mortices and tenors ought to be nearest the side on which the pressure is, by which the timber will not be so much weakened; and hence it is the constant practice to cut the mortices and tenons as in figs. 664, 665. By the method shown in the last-named figure, the tenon obtains more strength from an additional bearing below, which is further increased by the inclined butment above, called a tusk. Fig. 664. Fig. 665. 2009. The method of framing wall plates together at an angle, for the reception of the hip rafter on the dragon beam, and the angle ties for retaining the wall plates in their places, is shown in fig. 666., wherein AB is the mortice cut for the tenon of the hip rafter shown in fig. 667. Fig. 668. is one of the wall plates, showing the halving to receive the other plate, and the cutting necessary for dovetailing the angular tie. Fig. 669. shows the method of cutting the mortices and tenons of principal and hip rafters; another method being given in fig 670., and to be preferred where a greater resistance to thrust is sought, because by it a double butting is obtained on the tie beam. Inasmuch, however, as in this last case the beam is cut across the grain to receive the rafter, the part left standing to receive the heel of the rafter may be easily split away; to obviate which, the socket may be cut, as at A, parallel to the grain of the wood. cd is the iron strap for securing the rafter's foot to the tie beam, and keeping it in its place. A plan of the upper part of the tie beam is given c at B, showing the socket and mortice of the section A in the last figure. Fig. 671. Fig. 670. B C exhibits the 2011. Straps in carpentry should be sparingly used. Professor Robison has very properly observed, that "a skilful carpenter never employs many straps, considering them as auxiliaries foreign to his art." The most important uses of them are, that of suspending the tie beam to the king-post, and of securing the feet of the principal rafters to the tie beams in roofs. 2012. Bolts are sometimes used for the last-named office, with washers and heads and screw nuts, in which case the washers, nuts, and heads should be well painted, though even then they are liable to rust. Wherever the iron work used for securing a system of framing is exposed to the humidity of the atmosphere, it should be rendered durable by frequent painting. Price (British Carpenter, 1759) observes thus: " There is one particular that had liked to have escaped my notice, concerning the placing of iron straps on any truss, thereby meaning to help its strength, which is by turning the end square (as shown at E, fig. 671.). This method embraces the timber in such a manner, to make it like a dovetail, which cannot draw from its place; another observation is, to bolt on your straps with square bolts, for this reason: if you use a round bolt, it must follow the auger, and cannot be helped; by this helping the auger-hole, that is, taking off the corners of the wood, you may draw a strap exceeding close, and at the same time it embraces the grain of the wood in a much firmer manner than a round pin can possibly do." The example given by Price, however, for turning square the strap, is injurious to the rafter, which must be partially cut to admit of it. FLOORS. 2013. The assemblage of timbers in a building, used for supporting the flooring boards and ceiling of a room, is, in carpentry, called naked flooring, whereof there are three different sorts, viz. single flooring, double flooring, and double-framed flooring. But before entering on the particulars of either of the sorts, we will make some general observations on the construction of floors, which require the architect's attention. FIRST, the wall plates, that is, the timbers which lie on the walls to receive the ends of the girders or joists, should be sufficiently strong and of sufficient length to throw the weight upon the piers. SECONDLY, if it can be avoided, girders should not lie with their ends over openings, as doors or windows; but when they do, the strength of the wall plates must be increased. To avoid the occurrence in question, it was formerly very much the practice in this country, and indeed is still partially so, to lay girders obliquely across rooms, so as to avoid openings and chimneys, the latter whereof must indeed be always attended to. THIRDLY. Wall plates and templets must be proportionately larger as their length and the weight of the floor increases. Their scantlings will, in this respect, vary to 4 by 3 inches, up to 7 by 5 inches. FOURTHLY. The timbers should always be kept rather higher, say half to three quarters of an inch higher, in the middle than at the sides of a room, when first framed, so that the natural shrinking and the settlement which occurs in all buildings, may not ultimately appear after the building is finished. Lastly, when the ends of joists or girders are supported by external walls whose height is great, the middles of such timbers ought not at first to rest upon any partition wall that does not rise higher than the floor, but a space should, says Vitruvius (lib. 7. c. 1.), be rather left between them, though, when all has settled, they may be brought to a bearing upon it. Neglect of this precaution will induce unequal settlements, and, besides causing the floor to be thrown out of a level, will most probably fracture the corners of the rooms below. 2014. SINGLE FLOORING is constructed with only one series of joists (as shown in fig. 672.). In this way of framing a floor, if a girder is used, it should be laid as nearly as possible over the centre of the apartment. A single floor containing the same quantity of timber as a double floor is much stronger; but the ceiling of the former is liable to crack, and cannot be got to so Fig. 672. good a surface when finished. Hence, where the bearings are long, it is much better to use double flooring. 2015. The scantlings of fir joists for single flooring are exhibited in the subjoined table, and are founded on our own practice. The weight of a square varies from 11 to 18 cwt. These scantlings may be varied if wanted, according to the laws laid down in the section BEAMS, PILLARS, &c.; 1622. et seq. 2016. In fig. 672. AAA are the joists, and B the noor boards. The laths for the ceiling are nailed to the under side of the joists AAA, 2017. In most floors, on account of the intervention of flues, chimney openings, and occasionally other causes, it will so happen that the ends of the joists cannot have a bearing on the wall. In such cases a piece of timber called a trimmer is framed into two of the nearest joists (then called trimming joists) that have a bearing on the wall. Into the trimmer, which is parallel to the wall, the ends of the joists thus intercepted from tailing into the wall are mortised. The operation is called trimming. The scantlings of trimmers and trimming joists may be the same as those hereafter given for binding joists; or if to the width of the common joists an eighth of an inch be added for each joist supported by the trimmer, the depth being the same, the scantling will generally be sufficient. 2018. When the bearing of a single joist floor exceeds 8 feet, a row of strutting pieces should be introduced between the joists, by which they will be prevented from horizontal twisting, and the floor will be stiffened. If the bearing be more than 12 feet, two rows of stiffening pieces or struts should be introduced, and so on for each increase of 4 feet in bearing. They should be put in, in continued rows, and be well fitted. Beyond a bearing of 15 feet it is not advisable to use single flooring, neither ought it in any case to be used where it is required to prevent the passage of sound. 2019. A double floor consists in its thickness of three tiers of timbers, which are called binding joists (these perform the office of girders), bridging joists, and ceiling joists. From an inspection of fig. 673. the construction will be easily understood. AA are the binding joists, which are the principal support of the floor on the upper side, whereon BB, the bridging joists are notched; which is the best method, though sometimes they are framed between with chased mortices. The binders, of course, run from wall to wall; and as for carrying the floor, the bridging joists, as their name imports, are bridged on to them; so the lower tier of timbers, called the ceiling joists, are either notched to them, or are what is called pulley mortised into them; that is, a chase D is cut in the binder long enough to allow tenons of the ceiling joists C being obliquely introduced into them, and driven up to their places. The scantlings of timbers used in this method are the same as those for double-framed flooring of which, indeed, it is but a species. 2020. The double-framed floor differs only from the last-named by the binding joists, instead of going from wall to wall, being framed into large Fig. 674. D, and F is the floor. The great advantages of this sort of flooring are, that it prevents the passage of sound between the stories, and enables the architect to make a solid ceiling. 2021. As in a double-framed floor the girders are the chief supports, it is exceedingly important that they should be sound and free from shakes. The distances between one girder and another, or the wall, should not exceed 10 feet, and their scantlings as n the following table: Girders of the length of 10 feet should be 9 inches deep, 7 inches wide. 2021a. Girders or beams whose bearing exceeds 24 feet are difficult to be procured of sufficient depth, in which case an expedient is put in requisition to strengthen a less depth. The principles it involves are explained under the head of roofs, namely, those of trussing them (2031, et seq.), an operation that converts the beam within its own thickness into a piece of framework, for the purpose of preventing the bending, or, as it is technically called, its sagging, which produces an injurious horizontal thrust on the walls. This operation is represented in fig. 675, in two different ways. No. III represents the plan. The beam is cut into two halves in the direction of its depth and length, between and into which the truss is inserted, as shown. It is better that the truss posts A, and abutment pieces B, should be of wrought iron; the struts C may be of oak, or some stiffer wood than the beam itself. In I. and II., the whole, or nearly the whole of the timber, is in a state of tension. 2021b. This operation is further developed by trussing the beam below itself, an arrangement considered to be safer and stronger than that above described. a wrought iron tension od, with a stay in the V. centre, which takes the whole of the tension, whilst the timber is thrown e..tirely into compression. No. V. is the same with IV. No. IV. has port its own weight safely, may be made to carry a load of many tons without sensible deflection. The tension rod is useful in proportion to its distance from the beam (evidently within certain limits). If it be immediately under, or concealed within the under edge, it becomes nearly useless, especially in a cast iron beam with a wrought iron rod, where the beam is much less extensible than the rod. In such a case, the beam would break and fall before the rod has been brought into action. The respective size or sectional area of the rod and beam is regulated by the respective strength of the materials, as it is useless to apply a rod capable of sustaining double the tensile force that the bean can resist of crushing force, and vice versâ; it is merely adding weight (Warr, Dynamics, page 259.). The flitch girder is described in par. 1629u. 2021c. The resistance of beams of soft wood may be considerably increased by strengthening the centre of gravity. Du Hamel, Force des Bois, took twenty-four sticks, cut from young willows, of equal strength. Each stick was 3 feet (French) long, and 14 inch square. Six of these broke in the middle with an average weight of 566-48 lbs. In two other pieces he made a cut across it inch deep in the centre, and filled it out with a piece of oak; these broke with an average weight of 594-73 lbs. Two more were cut inch deep, and treated in the same manner; they broke with 585 lbs. Five were cut inch deep, and broke with 572 78 lbs. All the trials showed that the piece of harder wood increased the strength of the beam. 2021d. Laves's girder is a simple and effective contrivance for strengthening a beam. The piece of timber having been cut nearly from end to end (fig. 675a.), is bound at each Fig. 675a termination with an iron strap. Blocks are driven in the cut so as to separate the severed picces to several inches distance in the middle of the length, thereby throwing |