Chapter VI.THE WOOD-WORK. CARPENTRY.
Having thus briefly noticed the principal kinds of timber, and some of the modes of bringing it to market, we have in the present chapter to trace the wood through the various processes whereby it becomes part and parcel of a house.
When a timber-tree is felled, the branches, arms, and boughs, are cut off, and the bark stripped, this being valuable for many purposes. The trunk is then sawed square, and again cut intoplanks,deals,battens, &c., as the different-sized boards into which it is reduced are called.
Teak and mahogany are imported into this country inlogs, distinguished from the long beams known technically astimber, by their width and thickness being considerable in proportion to their length.
Timber is sawed in countries producing, or using it, in great quantities in saw-mills, in which the tools are worked by water or steam, as described in the last chapter; and it is also sawed into battens, laths, &c., by circular saws, turned by machinery, like a lathe; but when timber is sawed by hand, it is done by two men acting in concert in the following manner:—A pit is generally chosen, round the margin of which a stout frame is laid. The beam to be sawed is laid along the centre of this frame, in the direction of the length of the pit. One man stands on the beam while another is in the pit below him, and each alternately raises or pulls down a large vertical saw, with which the beam is cut lengthwise into planks. Wedges of wood are placed in the fissure as the work proceeds, to keep the cut open, and thus allow the saw to play freely. This is very hard labour, especially to the upper man, who has not only to raise the weight of the saw in the up-stroke, but to guide it correctly along the chalked line on the beam. This man gets higher wages, and is called thetop-sawyer, a term technically given in jest to any one who is, or fancies himself, of superior importance.
When timber is wanted in lengths exceeding those that can be procured from the tree in one piece, it must be joined by what is calledscarfing; that is, the ends of the two lengthsthat are to be united into one, are cut so that a portion of the one may lap over and fit into a portion of the other, which is cut so as to receive it. The timber, when united, is thus of the same uniform size. The joined ends are secured together by bolts or spikes. The following figures show the more usual modes of scarfing timber for different purposes.
The last is a mode of scarfing invented byMr.Roberts, of the Royal Dock Yards.
When a beam of timber is long in proportion to its breadth and thickness, it will bend by its own weight, and will beincapable of supporting much additional load; it may be strengthened bytrussing, in different modes, of which we will only describe that usually adopted for girders, intended for floors. The beam is sawed longitudinally into two equal beams, each, of course, half the thickness of the original: these halves are reversed, end for end, so that if there were any weak part in the original beam, this may be divided equally between the ends of the compound beam made up of the two halves when bolted together. A flattruss, usually of oak, with ironking-boltsand abutting plates, resembling in form and principle a timber roof or bridge, is placed between the two half beams, and let into a shallow groove cut in each half to receive it; the compound beam, with this truss in the middle, is then bolted together again by means of iron bolts, with washers and nuts, and consequently becomes rigid by the construction of the truss. The truss is not entirely let into the double beam, as the full effect of strength may be obtained without the necessity for cutting the groove in each half beam of half the thickness of the oak truss; consequently, when the girder is completed, there is a slit all along it, through which the truss is seen lying in its place between the two sides.
Iron trusses are often used instead of oak, and beams are frequently strengthened by screwing a thin flat iron truss on one or both sides, let into the beam for about half the thickness of the metal.
Strengthening a beam with trusses
This mode of strengthening a beam by trussing is only adopted in floors, where it is necessary to limit the depth of the truss to that of the beam, to obtain a level surface by means of joists laid across, and supported by, the beam. But it is obvious that much greater strength may be imparted to along beam by making it the base of a triangular frame, as is done in roofs, in various manners, when the slanting sides of the triangular frame carry the battens or laths for supporting the tiles or other covering.
The annexed is the simplest form of a roof, and will help to explain the subject of carpentry in other respects. The beamA, called thetie-beam, is of such a length as to rest on the side walls of the house at each of its ends, and is supposed to be of such dimensions in depth and thickness as would render it inadequate to support much more than its own weight. The two sloping raftersB B, are calledprincipals; they aremortisedinto the tie-beam at their ends by a joint, shown in the lower figure, by which they are provided with a firm abutment, to prevent the ends from slipping outwards; and in order to prevent the principal from starting upwards out of the mortise, it is strapped down to the tie-beam by an iron strap, bolted or screwed to both timbers.
Beams of a roof
Pis termed aking-post, and is cut out with a head and foot, the former to receive the upper ends of the principals, which, being cut square, abut firmly against the sloping face of the head. The sloping principals hold up the king-post, and the tie-beam is supported from the latter by a stirrup-shaped strap, that goes under the beam, and is bolted, or screwed, to the post on each side. To prevent the principals from bending by the strain, or by the weight of the roof covering, the strutsC C, are placed, abutting against the bevelled part of the foot of the king-post, and are strapped to the principals, or mortised into them.
The number of tie-beams, with their trusses, &c., of course depends on the length of the roof, or the material with which it is to be covered. A longitudinalscantling, or thin beam, called apurline,E, is laid lengthwise, resting on the principals over the ends of the struts, and is secured to the former by a spike, or else by being notched down on to the principal.These purlines support the common raftersR, which abut at their feet against a longitudinal scantlingS, lying on, andhalveddown on, the tie-beams; at their upper ends, the raftersRrest against aridge-piece, or thin plank, let edgeways into the head of the king-post. The rafters are placed about a foot apart, and on to them are nailed the laths or battens to carry the tiles or slates.
In constructing roofs, floors, and other structures of timber, the various beams areframed, or fastened together, by certain processes calculated to insure strength and permanence in the framing, which ought to be understood, and their names remembered.
TheMortiseandTenonjoint is used when one beam is to be attached to, and supported by, another, without resting on it, but so that the beams may be in the same plane. The mortise is a hole cut into, or through, the side of the one beam, into which hole the end of the other, cut down to fit the form of the hole, is inserted and fastened. It is obviously necessary to consider two things in determining the size and form of the mortise and tenon. First, that by the former the one beam may not be too much weakened, and yet that it should be large enough to give the tenon that fits into it, sufficient strength to enable the beam to carry the weight intended.
Mortise and tenon joint
If the one beam is horizontal, and the other to stand perpendicularly upon it, the tenon need only be large enough to retain the upright beam in its place. The foregoing figures are the most usual forms of mortises and tenons, and will explain their use and principle.
It is obvious that two mortises never should come opposite each other on the two sides of the same beam.
When the tenon comes through the beam, it is secured from drawing by a pin or peg put through it.
TheDovetailis used to secure one beam into another, when they have to resist any strain acting so as to draw them asunder, rather than to carry any weight; it is consequently employed to frame wall-plates, or the timber laid in walls to carry the ends of beams of floors, roofs, and so on, which plates tend to bind the walls together as well as to receive the ends of the beams. The term is derived from the end of one beam being cut into a shape resembling the spreading tail of a bird, which is pinned down in a corresponding wedge-shaped recess cut in the other beam to receive it. It is clear from this construction that no force, acting in the direction of its length, could pull the first beam out of the second without breaking off the dovetail, which the tenacity of wood-fibre renders nearly impracticable in one of any size. The dovetail is extensively used in all cabinet-making, and may be seen in almost any mahogany or deal-box.
Dovetail securing of beams
When two beams of equal thickness are required to cross one another and to lie in the same plane, they arehalvedtogether; that is, a notch is cut in each of half the thicknessof the other, then the uncut part of each lies in the notch of the other respectively, and the two are pinned together.
The smaller and better kind of work executed by the carpenter is calledJoiner’s work, such as the making of doors, windows, stairs, wainscotting, boxes, tables, &c. &c., which are usually formed of yellow or Norway deals, wainscot, or mahogany.
When a large surface is to be of wood, it is not formed of planks fixed together side by side till the requisite width is attained, but it is formed offramingandpanelling. A frame-work of the area required to be covered, is formed of narrow planks, with cross-bars between to strengthen the frame; these are calledstilesandrails, according to the directions in which they run, the former name being given to the upright planks of the frame, while the horizontal ones are called rails.
The rails are mortised into the stiles, and the tenons, since they must be comparatively thin, are made proportionably wide, nearly as wide as the rail. The tenons are always pinned into the mortise holes by one or two wooden pins driven quite through the stiles and through the inclosed tenon.
The edges of the stiles and rails areploughed, that is, a rectangular furrow is cut in the edge by means of a plane, to receive the ends and sides of thepanels. These panels are formed of thinner deals than the stiles and rails, and are made by glueing the edges of two or more boards together to make the proper width of the panel; the ends and edges of the panel are thinned off to fit into the groove or furrow in the stiles and rails, or else the ends and sides of the panel arerebated, that is, worked by a plane into the form shown in the following figure, the projecting part being received into the furrow.
As the panels are thinner than the frame, the former constitute so many recesses, at least on one side of the framing; and a small moulding is glued round the edge of the panel to form a finish to the work. Or else the same object is attained by working the edge of the stiles and rails with such a moulding, so that when the panel is put in, the moulding may finish against it. Sometimes the face of the panel is made to lie in the same plane with the face of the stiles and rails, and the panel is then said to beflush, and the edges ofthe stiles, &c., are finished with a small bead, also flush with the panel when finished.
Joined work
In joiner’s work the whole surface of the work is made perfectly smooth byplaningthe material, and allowance must be made for the reduction in thickness and width of the wood, produced by this planing, in the choice of the rough material.
All mouldings in wood are worked out by planes made of the proper form, to leave the moulding in the wood when the plane has been passed over the part. The carpenter and joiner consequently require a vast variety of planes for these purposes, which constitutes the most expensive part of the expensive tools used by these workmen. These planes receive their names from the form they are intended to produce in the wood, such asrebatingplanes, O G planes, ovolo-planes, beading-planes, and so on.
The next most important tools used by both carpenter and joiner, aresaws, of different sizes, for reducing the rough wood to the size adapted for the purpose to which it is to be applied. Small, fine-toothed saws, both long and thin blades, termed spring-saws, are used for cutting out small holes in wood, and for analogous purposes, when precision and nicetyare required; these spring-saws are sometimes mounted in a frame on the same principle as that of the stone-mason’s saw, formerly described; but commonly, the blade of the saw, of whatever size it may be, is only fixed on a convenient handle, so that the whole blade of the saw may pass through the fissure it makes in the material. All saws are made of the best steel, highly tempered, so as to recover their form if bent by the resistance of the wood.
Next to the planes and saws,chiselsare the most indispensable tool to the carpenter. Thesechiselsare of different widths, adapted to different uses, and are not only used with a hammer or mallet, as the mason employs them, but also as cutting-tools, used by hand for finishing the re-entering angles of mortise-holes, or for finishing the ends of pieces of wood too small to be planed.
The carpenter employsgimletsfor making holes for screws and nails. The gimlet is a short rod of steel, finished at one end into a sharp-pointed screw of one or two turns only, which, acting on the principle of that mechanical power, compels the tool to sink deeper and deeper into the wood, as the tool is turned round: and to enable the workman to turn the gimlet, it is fixed into a cross handle, which, acting as a lever, allows the friction of the tool to be overcome. Just above the screw point, the rod or shaft of the gimlet isflutedor hollowed out: the sharp edges of this fluted part cut the hole made by the screw end larger and smoother, and the hollow receives the chips or shavings cut off, and prevents them from clogging the hole and stopping the progress of the tool.
Augersare large tools shaped like a gimlet, and, acting in the same manner, are employed for making large holes for bolts, spikes, &c.Centre-bitsare steel tools of different shapes made to fit into a bent handle something like the letter G, which, acting as a lever, allows of the tool being turned round and round by one hand, while by the other the workman holds the top of the handle steady and vertically over the point of the tool. Some of thebitsor tools are for cutting out cylindrical holes, and are shaped at the cutting-edge like a chisel, with a small point projecting from the centre of the edge, on which the instrument turns in the wood and acts on the principle of a lathe. On each side this point, the chisel-edge is bent sideways in opposite directions, to allow of itsploughingup the wood before it with greater efficacy than it would do if it were not so formed.
Thebrad-awl, ornail-piercer, is a short steel wire, sharpened at the point into a flat chisel-edge, and put into aplain turned handle. This edge being pushed into the wood, and the handle turned round, the tool divides the fibre, and makes its way on the simple principle of a wedge, and does not cut away or remove any portion of the material, as the above-described tools do.
The carpenter uses nails and screws to fasten the different parts of his work together, and it is necessary to make a hole to receive them before they are driven in, or else the wood would split by the action of forcing the nail or screw into the solid material, and, indeed, it would be impossible to force a screw into the solid wood at all.
The screw is forced into the wood by being turned round and round by means of a blunt chisel, called ascrew-driver, the edge of which is inserted into a notch cut in the head of the screw to receive it.
Joiners fasten one piece of their work to another byglue, made by boiling down refuse animal matter containing the animal principle calledgelatinein abundance, such as hoofs, horns, tendons, skin, gristle, &c.: it is a property of gelatine to dissolve in hot water, and to harden again when cold, and the water evaporates. Accordingly the glue, which is only concentrated impure gelatine, is dissolved by heat in a small quantity of water, and being applied to the clean faces of the wood to be united, by a coarse brush, these faces are closely pressed and retained together till the water evaporates, when such is the tenacity of the glue, that the wood may be broken in another place as easily as at the glued joint. To enable glue, however, to act in this manner well, the wood should be clean, the parts to be glued well warmed before the glue is applied, and the joint should be close, or the parts accurately brought together.
Besides the before-mentioned tools and materials, and some others, such as hammers, axes, &c., which need not be described, carpenters and joiners use instruments for measuring and setting out their work, and for drawing on the surface of the material the forms into which it is to be reduced, or the shape and situations of portions of the material to be removed for the purposes of framing. The instruments are compasses, squares, rules, levels, plumb-lines, and so on, common to all artificers who form their materials into geometrical shapes: and, like the mason, the carpenter and joiner must be conversant with the more elementary problems of practical geometry.
In illustration of the nature of joiner’s work, we may point out the mode of proceeding in making a window-sash, which is one of the most delicate operations of the common joiner. The outer part of the sash is made broader and stronger than the intermediate cross-bars which receive the panes of glass, in order to give strength and rigidity to the sash. This outer part is framed together at the four angles by mortises and tenons, the latter coming quite through the stuff, and having a small sharp wedge driven into the middle of the tenon when inserted into the mortise: by means of this wedge, the tenon is expanded at its end into a wedge-shaped form, by which it fits more tightly into the mortise, and is retained in its place, the wedge-shape not allowing the tenon to be withdrawn again. But it may be here remarked, that, besides this precaution, all small mortises and tenons are put together with glue, to ensure the stability of the joint.
The inner edge of this frame is formed by aplaneinto the half moulding, of which the cross-bars present the entire section, so that when the sash is completed, each panel, as it were, which is filled in with the glass, is surrounded on its sides by a continuous moulding, and on the other side of the frame each panel presents arebatein which the glass lies. The annexed figure of the section of part of the outer frame and one cross-bar, will make this clear.
Joined window sash
The cross-bars are made in lengths out of slips of wood, by a plane, which first forms the mouldings and rebate on one side, and then by turning the slip over, the same plane finishes the other with an exact counterpart of the first. These bars are framed into the outer part of the sash by delicate mortises and tenons put together in the manner before described; but it will be seen by reference to the figure,that the moulded part of the bar must unite to that of the outer frame, or of another bar, by amitre-joint, that is, by one which allows of the lines of mouldings returning on the second piece, at right angles to their direction on the first, without any interruption to the continuity of the surface.
This and all analogous mitre-joints are formed by planing the ends of the wood to form a face, making an angle of 45° with the axis or length of the stuff, and the joiner is provided with a tool called amitre-box, consisting of a stock or frame, in which the stuff being put, resting against one another’s surface, guides the plane so as to cut off the end obliquely at the requisite angle. It is clear that this mitre must be made on both faces of the bar, and therefore the two mitre faces form a wedge-shaped termination by meeting at a right angle, as shown in the last figure. Now, as besides the mitre end, a tenon is to be left to fit into a mortise in the outer frame, it is clear that the whole must be a very nice piece of workmanship to be executed on so small a material as the thin bar of a modern sash.
The bevelled mitred end of the bar is received into a corresponding-shaped notch cut the depth of the half moulding in the outer frame to receive it, and at the bottom of this notch is the fine mortise-hole intended to receive the tenon.
The bars of the sash can, of course, only be made in one length in one direction, and the cross-bars which divide the long panels, formed by these continuous bars, into the sizes of the glass, are made of similar short pieces with mitred ends; but these ends, where they frame into the long bars, have no tenon, the thinness of the stuff not admitting of one, since the cross-bars come, end for end, opposite each other, on the two sides of the upright bars.
It is evident that the long bars must be put together with the outside frame, or else the tenons could not be inserted into the mortises made in this last.
In further explanation of joiner’s work, we will briefly describe the mode of making a drawing-board, requiring to betrue,plane, andsquare. Suppose the board is intended to be so wide as to require three boards side by side to make it: these three boards being sawn out of the right length, their edges are first planed perfectly straight and smooth, so that when any two are placed side by side, the edges touching, those edges may touch or fit together accurately for their whole length; this accuracy of joint is obtained by testing the edge after each time the plane is applied, by a straight-edge,or rule, known to betrue. There are two modes of proceeding to make these joints firm: one bydowelling, that is, by inserting short pieces of hard wood, as oak or wainscot, let for half their length into a mortise cut in the edges of the boards that are to fit together; these mortises, being, of course, made opposite each other, these dowels prevent the boards from rising up or starting from their places when the work is finished. Instead of short dowels, a strip, the whole length of the boards, is let into each joint, half the strip lying in a ploughed groove, made in the middle of the corresponding edges of the two boards. But, besides those precautions, the joints are well glued up.
There are two modes by which this board may be strengthened, to prevent itswarpingorcastingby the drying or shrinking of the wood. A cross-piece of deal, or better still, of wainscot, is fixed across the ends of the boards, these ends being double rebated ortongued, to fit into a groove made in the cross-piece to receive the tongue; these cross-pieces prevent the long boards from warping, since the cross-pieces would have no tendency to alter their figure in the direction of their grain.
If, however, the board be larger,keyingis better than this clamping. Keying consists in attaching two stout cross-pieces at the back of the boards, the faces of which pieces are worked so as to fit, and are glued into a dovetail-shaped groove cut across the direction of the boards at their back to receive the keys, as will be understood from the annexed sketch.
Keying of board
When the board is made, and the glued joints quite dry, the face is planed perfectly smooth and level, and the edges made truly square, or at right angles; if the board be keyed, the back must be planed smooth before the keys are put in.
The flooring-boards in the better kinds of houses are oftendowelledin the manner above described, and the ends of the flooring-boards are tongued and grooved to fit together, to prevent the boards from starting up from the joists and becoming uneven.
Beyond this point, it will be not necessary to trace the operations of the carpenter and joiner; for the sawing, scarfing, trussing, and joining large beams for the roof, and the minuter details connected with the window-sash, will illustrate pretty accurately the general nature of the whole routine of processes.