POINTS TO BE CONSIDERED BEFORE COMMENCING THE CONSTRUCTION OF A
CARRIAGE.—COMPONENT PARTS OF THE BODY.—SMITH’S WORK.—GLUE.
As previously remarked the vehicle is divided into two parts—the
carriage and the body. After the drawing or draught is carefully
worked out to full-size on the black-board in the shop, with all
the curves and sweeps developed, and shown in elevation and plan,
patterns or templates are made from the draught, and from these the
construction of the body proceeds.
In commencing the construction of a vehicle there are several things
to be borne in mind; such as the purpose to which the vehicle is to
be applied, the size of horses to draw it, and other considerations
arising from these two. It is popularly believed that the shorter the
carriage the lighter it will run; in ascending an incline this may be
true, but on ordinary level ground a long carriage and short one must
be alike in friction, provided the total amount of weight and other
circumstances be equally balanced.
Another consideration is the height of the wheels. On level ground,
draught is easiest when the centre of the wheel is a little lower
than the point of draught, viz. the point where the traces are
affixed to the collar; but this in practice would be found rather
inconvenient, as very high wheels would be required, and consequently
the height of the whole vehicle would have to be increased, causing
great trouble and annoyance in getting in and out of the vehicle,
and the driver’s seat would have to be raised to a corresponding
height. Under equal circumstances a high wheel is more efficient
than a low one, and requires less power to draw it; though it may be
mentioned that a low wheel on a good and level road will do its work
far better than a very much higher wheel on a rougher road. The sizes
of the wheels of two-wheeled vehicles vary from 3 feet to 4 feet 6
inches.
It would be a very good thing if four-wheeled vehicles were to have
the wheels of equal size, in order that the friction and power might
be equal. But with the present mode of construction this is an
impossibility, as we have only one mode of making the lock or turn.
Therefore the height of the fore wheels must be regulated by the
height at which the body hangs, so that the wheels may pass beneath
it without striking, when the springs play. In practice this height
varies from 2 feet to 3 feet 8 inches, according to the kind of
carriage the wheels are intended for. The hind wheels vary from 3
feet to 4 feet 8 inches.
The next point is the dishing of the wheel, which is necessary for
strength to take the strain off the nuts, to throw off the mud and
prevent it clogging either the wheel or the body, and to give greater
room for the body between the wheels without increasing the track on
the ground. Whatever be the amount of dishing or coning, which varies
from 1½ to 2½ inches, one rule should always be observed, viz. so to
form the wheel that when running the lower spokes should maintain
a true vertical position both in the fore and hind wheels. This is
mainly accomplished by the dip of the axle, but if the fore and hind
wheels have the same dish, they will take the same track along the
ground. The dish of a wheel will be understood by referring to Fig.
10, in which it will be seen that the extremities of the spokes are
not in the same plane, thus forming a dish or hollow in the surface
of the wheel.
[Illustration: Fig. 10.]
Some ingenious persons have deduced from the foregoing that a wheel
runs best on an axle having a conical arm (the arm is the extremity
of the axle which fits into an axle-box in the nave or stock of the
wheel), in which case the axle would not dip, but the wheel would be
put on to a perfectly horizontal axle. The motion of a wheel thus
placed would be anything but artistic, though there would not be
so much friction on an arm of this sort as on an arm of the dipped
axle. Dipping the axle is shown at Fig. 10. It merely consists in
bending it so far out of the horizontal as to give the lower spokes
a vertical position. But in practice this theory of the conical arm
will not answer, inasmuch as curving the arm will reduce the front
bearing surface so much that the oil would be squeezed out, and it
would run dry, and the total amount of friction would be greatly
increased. Long practice has shown that a cylindrical or slightly
conical arm is the best that can be used.
We have now to settle the form, combination, and proportion of the
springs. Springs which are laid on the axle at right angles have
to carry the whole of the weight of the carriage, save only the
wheels and axles. Where other springs are used in addition it is
not necessary that the axle-springs should have much play. It will
be sufficient to give them just so much play as will intercept
the concussion caused by moving over a road. The strength of the
springs must of course be adjusted to the weight they have to carry,
for it is evident that if they be made sufficiently elastic to
carry the weight of six persons, they will be found hard if only
three enter the carriage. This is a disadvantage all carriages must
labour under, for it is ridiculous to suppose that if a carriage is
constructed to hold six that number will always want to use it at
the same time. There would seem to be room for some improvement in
the way of introducing springs adjustable to any weight, though, to
give spring-makers their due, they do turn out really a first-class
article in this respect; this is more noticeable because it is so
recent. Light carriages are never so easy to ride as heavy ones,
even when the springs are well adjusted, because on meeting with an
obstacle there is not a sufficient resistance to the bound or jerk
upwards of the spring, which makes riding in a light carriage over a
rough road rather unpleasant.
The position of the front wheels next demands attention. As these
have to turn under the body it requires some skill to fix them, and
the play of the springs, the height of the axletree, and the height
of the arch (the portion of the body under which they turn) have
all to be considered. This will be more particularly described when
dealing with wheel-plates.
The rule for the height of the splinter-bar, to which the traces or
shafts are fixed, is that it should fall on a line drawn from the
horse’s shoulder to the centre of the hind wheel. This, however,
is not always convenient in practice, as the fore wheels regulate
the height of the framing of the under carriage, to which the
splinter-bar is fixed. The distance of the splinter-bar from the
central pin, on which the wheel-plate and fore carriage turn, is
regulated by the size of the wheels and the projection of the driving
seat footboard.
All the above particulars are considered when setting out the
full-sized draught, and all points capable of delineation are put on
the board in some convenient part. In Fig. 9 the outline is simply
given, as to show everything would only confuse the reader. Such
other details as are required are filled in after the draught has
reached the stage shown in the figure.
It is most necessary for the safe conduct of a coach and carriage
builder’s business that there should be a goodly stack of
well-seasoned timber of the various kinds required, otherwise great
trouble and vexation will arise in the course of business from a good
piece of timber being perhaps spoilt in working, and there not being
another piece in the factory to replace it.
Where there is sufficient accommodation it is usual for makers
to season their own timber in specially constructed sheds, which
are kept from bad weather, but at the same time thoroughly well
ventilated. In these the timber is stacked, with small fillets
between each plank or board, to insure a free current of air
circulating all round. One year should be allowed for seasoning for
every inch of thickness in the timber, and none should be used in
which this rule has not been observed.
Thin portions of timber, such as panel stuff and the like, should be
treated in the same way, and in addition the ends should be secured
to prevent splitting. The panel stuff undergoes another process
of seasoning after it is planed up; in fact, all the thin timber
required for roofs, sides, &c., does. And about the first thing done
in commencing to build a carriage is for the body-maker to get his
thin stuff ready, as far as planing it up goes, and then to put it
aside in some moderately dry place, with slips of wood between each
board to allow a circulation of air round them. The other stuff that
is likely to be required should also be selected and put aside. If
all these things be strictly attended to, there is not likely to
be much trouble about bad joints; and it will be to the employer’s
interest to look after such workmen who have not enough scientific
knowledge to see the reason of things themselves, and put them in the
right direction. But an intelligent workman will soon appreciate the
advantage of getting his stuff ready at the commencement, instead of
waiting till he wants to use it.
The parts composing the body may be thus enumerated:—
The frame or case.
The doors.
The glasses, which are fixed in thin frames of wainscot,
covered with cloth or velvet. It is a very good thing to have
india-rubber for these to fall on, and little india-rubber buffers
would prevent them from rattling.
The blinds, which are sometimes panel, but more generally
Venetian, so adjusted with springs that the bars may stand
open at any required angle.
The curtains, of silk, which slide up and down on spring
rollers.
The lining and cushions, of cloth, silk, or morocco, as the
case may be, ornamented with lace, &c. The cushions are
sometimes made elastic with small spiral springs.
The steps, which are made to fold up and fit into recesses
in the doors, or in the bottom, when they are not in use.
The lamps, which are fixed to the fore part of the body by
means of iron stays.
The boot, on which is carried the coachman’s seat.
In carriages suspended from C springs we have in addition:—
The check-brace rings, to which are attached leather braces
from the spring heads, to prevent the body from swinging
too much backwards and forwards.
The collar-brace rings, to which are attached leather braces
from the perch, to prevent the body swinging too much upwards
or sideways.
The curve or rounding given to the side of the body from end to end
is called the _side-cant_, and the rounding from the top to the
bottom the _turn-under_. Some makers arrive at this curve by framing
the skeleton of the body together with square timber, and then round
these off to the required curve _after_ they are put together. It
must be evident to any one that this proceeding will greatly strain
the joints, and under any circumstances will never give thorough
satisfaction or good results, and the waste of time and material must
be very considerable.
The proper way is to set the curve out beforehand on a board called
the “cant” board, and the method of doing this is as follows:—
Take a clean pine board, plane it up to a smooth surface. Shoot one
edge perfectly true with a trying-plane. This straight edge may be
taken to represent the side of the carriage if it were a straight
line. Apply this edge to the full-sized draught, and mark along it
the various parts of the body (see Fig. 8, in which the numbered
points are those required to form the side-cant). By means of these
points the required sweep can be set up or drawn, as shown by the
dotted line C in the figure. Now, if you choose, you can cut away the
portion between A and B, and a template will be formed to which the
constructional timbers can be cut; and it possesses the advantage
of being easily applied to the carriage as it proceeds, to see that
the curve is true and uniform. As this template forms the pattern to
which the timber, &c., is cut, great care is requisite in forming it,
so that it shall be perfectly true.
In order to get the turn-under, the same process is gone through
on another board. This gives what is called the “standing” pillar
pattern, the standing pillar being the upright timber to which the
door is hinged.
There is no rule in particular for determining the amount of
side-cant or turn-under to be given to a vehicle, 2½ or 3 inches on
each side making the outside width of the body; 5 or 6 inches less at
the bottom than at the elbow line is a usual allowance, but this is
entirely dependent on the will or taste of the workman.
The cant-board described above is one having a “concave” surface; but
it quite as often has a convex surface, and it is just as well to
have one of each, and use the convex for cutting the timbers to, and
the concave for trying them when in place, though, if this be done,
it is imperative that the curves on the two boards should be one and
the same. The same remarks apply to the standing pillar pattern.
The body is a species of box, fitted with doors and windows, and
lined and wadded for the purpose of comfort. As the greatest amount
of strain is put upon the bottom part, and the forces acting on the
other parts are transmitted to the bottom, it is necessary that it
should be very strongly put together. The two side bottom timbers
are bonded, or tied together, by two cross timbers called bottom
bars, which are firmly framed into them. To give depth to the floor,
without destroying the symmetry of the side, deep pieces of elm plank
are fixed to the inside of the side bottom pieces, and to these the
flooring-boards are nailed, being additionally secured by iron strap
plates, nailed or screwed beneath them. In the central portion of the
bottom sides are framed the door-posts, called standing pillars. At
the angles of the bottom framework are scarfed the corner pillars.
The cross framing pieces, which connect the pillars, are called
rails. Two of these rails stretch across the body inside, on which
the seats are formed; these are called seat rails. The doors are
framed double, to contain a hollow space for the glasses and blinds,
and they are fastened by means of a wedge lock, forced into a groove
by a lever handle. There is a window in each door and one in front
of an ordinary carriage, say a brougham. The doors are hinged with
secret or flush hinges.
Before cutting the timber to the various sizes required, patterns or
templates of all the parts are made in thin wood from the full-sized
draught; also of the various curves likely to be given to the
different parts of the body.
Before a workman could be trusted with the making of a body, he must
of course have considerably advanced in the knowledge of his craft
beyond the mere use of his tools, because the success of a carriage
depends very largely upon the individual skill of the workman, more
so than perhaps in any other trade.
The stuff is marked out from the thin patterns before mentioned
by means of chalk, and in doing so care should be taken to lay
the patterns on the timber so that the grain may run as nearly
as possible in a line with it, and thus obtaining the greatest
possible strength in the wood, which lies in the direction of the
grain. Thus if the pattern be straight, lay it down on a piece of
straight-grained timber; if the pattern sweep round, then get a piece
of timber the grain of which will follow, or nearly follow, the line
of pattern.
The strongest timber that can be obtained is necessary for the
construction of the hind and front bottom sides; for the weight is
directly transmitted to these, more particularly the hind bottom
sides, where the pump-handles are fixed.
The body-maker, having marked and cut out the various pieces of
timber he will require, planes a flat side to each of them, from
which all the other sides, whether plain or curved, are formed and
finished. They are then framed and scarfed together, after which
the various grooves are formed for the panels and rebates, for the
floor-boards to fit on to. Then, if there is to be any carved or
beaded work, it is performed by the carver. Previous to being fitted
in, some of the panels have strong canvas glued firmly on their
backs, and when fitted in blocks are glued round the internal angles
to give greater security to the joints, and to fix the panels firmly
in their places. Before the upper panels are put in, the roof is
nailed on, and all the joints stuck over with glued blocks inside.
The upper panels are then put on, united at the corners, and blocked
inside.
If the foreman who superintends all this be a thoroughly skilful
artisan, and the men under him possess equal intelligence and skill,
the work might be distributed amongst almost as many men as there are
parts in the framework of the body. These parts will be worked up,
the mortises and tenons, the rabbets and tongues, being all cut to
specified gauges; and when they are all ready it will be found that
they go together like a Chinese puzzle.
The woodwork being completed, the currier now takes the body in
hand, and a hide of undressed leather, specially prepared for it, is
strained over the roof, the back, and the top quarters of the body
whilst in a soft pulpy state, and carefully sleeked or flattened down
till it is perfectly flat. This sleeking down is a rather tedious
process, and takes a long time and a great amount of care to bring it
to a successful issue; when it is flattened down satisfactorily, it
is nailed round the edges and left to dry, which will take several
days.
Such panels as require bending may be brought to the required sweep
by wetting one side and subjecting the other to heat, as of a small
furnace.
The doors are now made and hinged, and the hollow spaces intended
to hold the glasses and blinds are covered in with thin boards, to
prevent any foreign matter from getting down into the space, and
being a source of trouble to dislodge.
In constructing the body the aid of the smith is called in. His
services are required to strengthen the parts subjected to great
strain, more particularly the timbers forming the construction of the
lower portion. All along each side of the body should be plated with
iron; this should be of the best brand and toughest quality. It is
several inches wide, and varies from ¼ to ¾ of an inch in thickness.
This is called the “edge plate,” and is really the backbone of the
body, for everything depends on its stability. It should run from
one extremity to the other, commencing at the hind bottom bar, on
to which it should be cranked, and ending at the front part of the
front boot, bottom side. This plate should take a perfectly flat
bearing at every point. Great care must be taken in fitting it, for
although the plate may be of the requisite strength the absence of
this perfect fitting will render it comparatively weak, the result
of which will be found, when the carriage is completed and mounted
on the wheels, by the springing of the sides, which will cause the
pillars of the body to press on the doors, and it will be a matter of
great difficulty to open them.
In the application of smith’s work to coach-building, it is often
necessary to fit the iron to intricate parts while it is red hot, and
if due precaution be not taken the wood becomes charred and useless,
and in cases where there are glued joints it may cause the loosening
or breaking of these joints and other material defects. It is an
easy matter to have the means at hand to get over the difficulty.
All that is necessary is to have handy some heat neutraliser. One of
the commonest things that can be used is chalk, and no smith’s shop
should ever be without it. If chalk is rubbed over the surface to
which the hot iron is to be applied it will not char or burn. Plaster
of Paris is a still more powerful heat neutraliser, and it is freer
from grit. A small quantity of the plaster mixed with water, and
worked up to the proper consistency, will be ready for use in about
two hours. Many smiths will say that they never have any accidents in
applying heated iron, but on inquiry the reason is apparent, for it
will generally be found that such men use chalk, in order to see that
the iron plate takes its proper bearings, thus inadvertently using
a proper heat neutraliser. If it were more generally known that the
difficulty could be met by such simple means, there would be less
material spoilt in the smith’s shop.
It has been very common of late years for body-makers to use glue
instead of screws and nails for panel work, &c.; but it requires
a great deal of experience for a man to use glue with successful
results. It is useless for the tyro to try it; he will only spoil the
work. So, unless the artisan be well experienced in the treatment
and application of glue, he had better leave it alone. To render the
operation successful two considerations must be taken into account.
_First_: To do good gluing requires that the timber should be well
seasoned and the work well fitted. _Second_: In preparing for gluing
use a scratch plane or rasp to form a rough surface of the pieces
to be joined together, for the same purpose that a plasterer scores
over his first coat of plaster-work, in order to give a key or hold.
The shop in which the gluing is done should be at a pretty good
temperature, and so should the material, so that the glue may flow
freely. Having the glue properly prepared, spread it upon the parts,
so as to fill up the pores and grain of the wood, and put the pieces
together; then keep the joints tight by means of iron cramps where
it is possible, and if this cannot be done the joints must be pushed
tightly up, and held till the glue is a little set and there is no
fear of its giving way. All superfluous glue will be forced out by
this pressure and can be cleaned off.
A great cause of bad gluing is using inferior glue and laying it on
too thick. Before using a new quality of glue, the body-maker should
always test it by taking, say a piece of poplar and a piece of ash,
and glue them together, and if when dry the joints give way under
leverage caused by the insertion of the chisel, the glue is not fit
for the purposes of carriage-building and should be rejected. With
good glue, like good cement, the material should rather give way than
the substance promoting adhesion. This is a very severe test, but in
putting it into practice you will be repaid by the stability of your
work.
_Waterproof Glue._
It is often found that joints glued together will allow water to
dissolve the glue, and thereby destroy its adhesive power. It may
have been well painted and every care taken to make it impervious to
water, but owing to its exposed position water has managed to get in.
Often where screws are put in the glue around them will be dissolved,
caused by the screws sweating; and it is very often found, where the
screws are inserted in a panel, that the glue loses its strength
and allows the joint to open, and there is little or no appearance
of glue on the wood, which shows that it has been absorbed by the
moisture.
To render ordinary glue insoluble, the water with which it is mixed
should have a little bichromate of potash dissolved in it. Chromic
acid has the property of rendering glue or gelatine insoluble. And,
as the operation of heating the glue pot is conducted in the light,
no special exposure of the pieces joined is necessary.
Glue prepared in this manner is preferable in gluing the panels on
bodies, which are liable to the action of water or damp. The strength
of the glue is not affected by the addition of the potash.
In plugging screw holes glue the edge of the plug; put no glue into
the hole. By this means the surplus glue is left on the surface, and
if the plug does not hit the screw it will seldom show.
Where brads are used the heads should be well set in; then pass a
sponge well saturated with hot water over them, filling the holes
with water. This brings the wood more to its natural position, and it
closes by degrees over the brad heads. The brad must have a chance
to expand, when exposed to the heat of the sun, without hitting the
putty stopping; if it does it will force the putty out so as to show,
by disturbing the surface, after the work is finished.