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.
Sawing Timber.
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 into _planks_, _deals_,
_battens_, &c., as the different-sized boards into which it is reduced
are called.
Teak and mahogany are imported into this country in _logs_,
distinguished from the long beams known technically as _timber_, 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 the _top-sawyer_, a
term technically given in jest to any one who is, or fancies himself,
of superior importance.
Scarfing or Joining Timber.
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 called
_scarfing_; that is, the ends of the two lengths that 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.
[Illustration]
The last is a mode of scarfing invented by Mr. Roberts, of the Royal
Dock Yards.
Trussing or Strengthening.
When a beam of timber is long in proportion to its breadth and
thickness, it will bend by its own weight, and will be incapable of
supporting much additional load; it may be strengthened by _trussing_,
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 flat _truss_, usually of oak, with iron _king-bolts_ and 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.
[Illustration]
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 a long 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 beam A, called the
_tie-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 rafters B B, are called
_principals_; they are _mortised_ into 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.
[Illustration]
P is termed a _king-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
struts C 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 longitudinal _scantling_, or thin beam, called a _purline_, 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 rafters R,
which abut at their feet against a longitudinal scantling S, lying on,
and _halved_ down on, the tie-beams; at their upper ends, the rafters R
rest against a _ridge-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.
The Mortise and other Joints.
In constructing roofs, floors, and other structures of timber, the
various beams are _framed_, or fastened together, by certain processes
calculated to insure strength and permanence in the framing, which
ought to be understood, and their names remembered.
The _Mortise_ and _Tenon_ joint 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.
[Illustration]
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.
The _Dovetail_ is 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.
[Illustration]
When two beams of equal thickness are required to cross one another and
to lie in the same plane, they are _halved_ together; that is, a notch
is cut in each of half the thickness of the other, then the uncut part
of each lies in the notch of the other respectively, and the two are
pinned together.
Distinction between Carpentry and Joinery.
The smaller and better kind of work executed by the carpenter is
called _Joiner’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 of _framing_ and _panelling_. 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 called _stiles_ and _rails_, 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 are _ploughed_, that is, a
rectangular furrow is cut in the edge by means of a plane, to receive
the ends and sides of the _panels_. 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
are _rebated_, 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 be _flush_, and the edges of the stiles, &c., are
finished with a small bead, also flush with the panel when finished.
[Illustration]
In joiner’s work the whole surface of the work is made perfectly smooth
by _planing_ the 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.
The Tools employed.
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 as _rebating_ planes, O G planes, ovolo-planes, beading-planes,
and so on.
The next most important tools used by both carpenter and joiner,
are _saws_, 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 nicety are 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, _chisels_ are the most indispensable tool
to the carpenter. These _chisels_ are 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 employs _gimlets_ for 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 is _fluted_ or
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.
_Augers_ are large tools shaped like a gimlet, and, acting in the same
manner, are employed for making large holes for bolts, spikes, &c.
_Centre-bits_ are 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 the _bits_ or 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 its _ploughing_ up the wood before it
with greater efficacy than it would do if it were not so formed.
The _brad-awl_, or _nail-piercer_, is a short steel wire, sharpened at
the point into a flat chisel-edge, and put into a plain 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 a _screw-driver_, the edge of which is
inserted into a notch cut in the head of the screw to receive it.
The Glue employed.
Joiners fasten one piece of their work to another by _glue_, made by
boiling down refuse animal matter containing the animal principle
called _gelatine_ in 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.
A Window-sash, as an example of Joiner’s Work.
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 a _plane_ into 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 a _rebate_ in
which the glass lies. The annexed figure of the section of part of the
outer frame and one cross-bar, will make this clear.
[Illustration]
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 a _mitre_-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 a
_mitre-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.
A second example of Joiner’s Work.
In further explanation of joiner’s work, we will briefly describe the
mode of making a drawing-board, requiring to be _true_, _plane_, and
_square_. 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 be _true_. There are two modes of proceeding to make these
joints firm: one by _dowelling_, 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
its _warping_ or _casting_ by 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 or _tongued_,
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, _keying_ is 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.
[Illustration]
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 often _dowelled_
in 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.