WHEELS.
A wheel for a locomotive vehicle is a circular roller, either
cylindrical or conical, the width or thickness of which is
considerably less than its diameter. It may be either solid or
constructed of various pieces, in which latter case it is called a
framed wheel. It may also be made of wood or metal, or a combination
of both.
Wheels which were made before the introduction of iron were of course
very clumsy in their construction, in order to obtain the requisite
strength. Specimens may still be seen in the broad wheels of waggons,
technically termed rollers. The naves of these wheels are of enormous
size. But when the naves of wheels were reduced for the purposes
of elegance, a thin hoop of iron was applied both to the front and
back, to prevent them from bursting by the strain on the spokes. When
the felloes of wheels were reduced in size, straps of iron, called
strakes or streaks, were applied to their convex surfaces covering
the joints. But the last improvement was the most important of all,
namely, the application of a “hoop-tire” instead of what was called
the “strake-tire.” Mr. Felton, in his treatise on coach-building,
1709, says, “Many persons prefer the common sort of wheel on account
of their being more easily repaired than the hoop-tyre wheel; but
though repairing the latter is more difficult, they are much less
subject to need it.”
The earliest form of wheel was no doubt a slice of the trunk of a
tree; portions of this being cut out for the purpose of lightening it
would be the forerunner of spokes, or we should think the pieces left
running from the nave to the felloe would be. The only improvement
then effected for a very long period was making them of different
pieces of timber instead of all from one piece, though of course the
proportions of the parts would be considerably improved, if only for
the sake of appearance.
At the end of the seventeenth century, among the wealthier classes,
decoration was applied to coaches generally, and wheels in
particular, to an extent which would surprise us nowadays. These
latter were again ornamented as in the times of the old Roman Empire;
the spokes were shaped and carved, the rim moulded, and the naves
highly embossed; though, as may be imagined, there was a great want
of taste in the application of all this ornament.
Towards the end of the eighteenth century, the extreme height of
wheels extended to 5 feet 8 inches, which had but 14 spokes; wheels
5 feet 4 inches high had 12 spokes; wheels 4 feet 6 inches had 10
spokes; and the lowest wheels, 3 feet 2 inches high, had 8 spokes.
The naves were of elm, the spokes of oak, and the rims or felloes
of ash or beech. The rims of the higher wheels were often of bent
timber, in two or more pieces, and were bolted to the tires by one
bolt between each pair of spokes. The tire was put on in pieces,
until the hoop-tire came into general use, when it superseded the old
ones entirely. In consequence of the great height of the wheels it
was necessary to make the carriages very long, and the distance from
the front to the hind axletree was 9 feet 2 inches in a chariot, and
9 feet 8 inches in a coach, or about 8 inches longer than we should
consider necessary now.
These extreme sizes are now very seldom used, except in the case of
large dress or state carriages and coaches.
The form of wheel now generally preferred in practice is of the
dished or conical kind, and the axle-arm on which it revolves is
sloped or bent so far out of the horizontal that the lower spokes
are in a vertical position. Undoubtedly the friction is increased
by this arrangement, because a wheel on a horizontal axle runs
easiest and smoothest; and when the axle-arm is slanted downwards
towards the point the wheel has a tendency to bind harder against the
shoulder which butts against the nave of the wheel, and the friction
between the two is greater than would be the case if the axle-arm
were perfectly horizontal. This, however, is a very small objection,
inasmuch as this collar is firm and strong, and well fitted to
bear any strain that may be thrown on it by the wheel; whereas, if
the force acted in the other direction, or against the nuts and
linch-pins, there are very few that would last out a day’s journey.
The advantage of throwing the strain on the firm and strong shoulder,
which is well able to withstand it, is evident; and in this case, in
the event of the nuts or linch-pins falling off or giving way, there
is not so much danger of the wheel coming off at the moment the nuts
go, as its tendency when on a level road is to run upwards towards
the shoulder. Besides this, as the lower spokes are in a vertical
position, the upper ones spread considerably outwards, and thus
afford a greater space for the body between the wheels without the
track on the ground being increased; and another advantage is that
the mud collected by these conical wheels is thrown off away from the
carriage.
The hind wheels of an ordinary carriage vary from 4 feet 3 inches to
4 feet 8 inches; the fore wheels are from 3 feet 4 inches to 3 feet 8
inches. The number of felloes in each circumference varies according
to the number of spokes, two spokes being driven into each felloe;
14 to 20 spokes are a usual number for a hind wheel, 12 to 18 for a
fore wheel; however, there is no rule to guide one in the matter,
experience being the only teacher.
The wheels should be made with a due regard to the offices they have
to fulfil; but we are inclined to think that this branch of the trade
has not received that careful study which it deserves. Coachmakers
seem in such a hurry to produce a perfect vehicle all at once,
instead of beginning by improving the parts and then applying these
improvements to the whole.
[Illustration: Fig. 11.]
The mode of constructing a wheel is as follows:—
The timbers that are to be used should be well and carefully
selected. The nave or stock, which is sliced from the limb of a tree,
should be as nearly as possible the size required in its natural
growth, so that it will require little reduction beyond what it
receives in the lathe in bringing it up to the true circular form.
The reason of this is that the annual rings which mark the grain of
the timber should be as little disturbed as possible, as they are not
all of equal strength and durability, the outer rings being pretty
strong, but as they get nearer to the centre the wood is much softer.
If, then, this outer hard casing is cut away, even only in part, it
is signing the death-warrant of the poor nave, for the interior parts
of the timber are not nearly so capable of resisting the destructive
influences around, and in a very short time they will become
completely soft and rotten.
[Illustration: Fig. 12.]
As already remarked, the spokes should be cleft, not cut. The felloes
which form the outer periphery of the wheel should also be cut as
closely following the grain as possible.
When the wheelwright has carefully selected his timbers, he commences
work by turning the stock in the lathe to the size required. Then
he marks with a gauge of the same width as the spokes 4 circles as
shown at _a_ _a_ _a_ _a_, Fig. 13. The first and third of these mark
the position of the front or face spoke, and the second and fourth
mark the position of the back spoke. Two holes are then bored in each
mortise in succession, after which they are squared out with proper
chisels. Truth of eye and skill of hand are the workmen’s only guide
in this operation, though it is evident that it is the most important
operation of the whole, as upon it depend the accuracy and solidity
of the wheel when finished. The tenons of the spokes are then cut to
fit the mortises, parallel in their thickness, but in width they are
cut slightly taper-wise, _i.e._ the extremity of the tenon is made
about the same size as the mortise, but at the shoulder it is about
one sixteenth of an inch larger, so as to make sure of the tenon
filling the mortise when driven home.
[Illustration: Fig. 13.]
Before cutting the mortises the stock should be fixed at some
convenient angle, regulated by the amount of dish it is intended to
give the wheel. This is particularly necessary, or when the felloes
come to be fitted, if the mortise-cutting has been done in a slovenly
way, the dish will not exist at all, or if it does it will be in the
wrong direction.
Each alternate spoke is now driven in by the blows of a mallet to a
perfectly close bearing of the shoulder of the tenon, the workman
guiding it as best he can. But it is evident that the position that
the spokes will take is by no means certain. Owing to the wedge-like
form given to the tenon, the spokes are driven home very tight, and
wood not being of a homogeneous texture will yield more in one part
than in another; and the mortise, cut in the way that it is, must be
to some extent uncertain. Every alternate spoke being driven, or
those in the same plane, the remainder are driven in between them in
the same manner.
[Illustration: Fig. 14.]
In Fig. 13, _b_, _b_, _b_, are the mortises for the face spoke, and
_c_, _c_, _c_, the mortises for the back spoke. Fig. 14 shows a
section of an ordinary spoke, the hatched part showing the form of
the greater part of its length, and the plain lines completing the
rectangle show the extent of the swelling at the shoulder of the
tenon at the nave.
[Illustration: Fig. 15.]
Fig. 15 shows a very handy adjunct to the wheelwright’s shop; it is
called the “centring square.” It is found extremely useful in marking
and setting out the mortises for the spokes. Its construction is very
simple, being but a T square, whose stock is the segment of a circle.
A is the blade, B the circular stock, the extremities of which should
be protected by steel or brass, or, better still, have a steel edge
round the whole of the inner surface of the stock, so that it will
always keep true; for if it wears at all, of course its true circular
form will be destroyed, and it will be rendered useless. And another
important thing should be borne in mind, and that is to make the
upper edge, C, of the blade in a line with the centre of the curve
from which the circular head is struck; the reason of this will be
apparent to the most obtuse, for unless the lines radiate from the
given centre it is useless for the wheelwright’s purpose.
After the spokes have been driven in they are shaved off by the
spokeshave to their proper form, Fig. 14; and the lengths being
measured from the nave, the outer tenons are cut, sometimes square,
sometimes cylindrical, but leaving the back shoulder square to abut
on the felloe with greater firmness. In the manner of tonguing there
is a great deal of difference of opinion amongst wheelwrights;
that the tongues in size should be slightly in excess of the hole
or mortise to receive them, is a generally received idea, but a
difference of opinion exists as to the length. But certainly it seems
more reasonable to cut the tongues a little _shorter_ than the length
of the hole in the felloe to receive them, because when the tyre is
put on it shrinks in cooling and draws up all the joints. Now suppose
the tongues are a little longer than the holes, the shrinking of the
tire causes it to press on these; and as they are firmly fixed at the
nave, there is no escape for them, and the result is that the spoke
is seriously crippled. It is fair to say that there are many good
practical men who work in this latter way, and with to all appearance
good results, but it is evident that the principle is not a good one.
One of the difficulties in making light carriage wheels is to get the
spoke tightly into the felloe without splitting it, and the manner
of accomplishing this is more successfully done, not by making the
tongue on the spoke so large that it will fill the hole in the felloe
of itself, but by making the tongue rather smaller and slitting the
edges after it has been driven in, and then wedging up with small
wedges, just in the same manner that a joiner would wedge up the
mortises and tenons of a door.
When the wheel is so far progressed with it is laid on the ground,
and the felloes are ranged round it in the order they are to be
fitted. It is of the greatest importance that the holes should be
bored in the felloe in an exact radial line from the nave; if this is
not done, the spoke will have to be strained out of the straight line
in order to get it into the hole; this will put an undue pressure
upon it, and it is very likely that before the wheel has been long in
use the spoke will break off short at the felloe. The exact position
of all the mortises and joints should, therefore, be worked out on a
full-sized drawing, and this being accurately done, there will not
be much danger of going wrong. As the construction of a wheel is
somewhat analogous to the arch, it is considered that by giving the
felloes a number of joints the strength of the wheel is very much
increased. Whether this be so or not must be left to the theorists
to determine, as we have no trustworthy results from the various
experiments under this heading.
The number of felloes in a wheel is decided by its size and number
of spokes, two spokes being driven into each felloe. For an
ordinary-sized brougham the felloes should be seven in number for the
hind wheels, and six for the front wheels, or fourteen and twelve
spokes respectively. For the purpose of connecting the felloes, a
dowel or pin is cut on the end of one of them, and a corresponding
hole bored on another, and they are fitted together; in common work
holes are bored in each felloe, and an independent pin of hard wood
or iron fitted into them. There is less time and labour consumed in
this latter method; but the felloes constructed on this plan are not
very reliable, and their weakness is soon shown by what is known as
“dropping,” which is simply caused by the wear and tear to which
wheels are subject working the dowels in the holes and enlarging them
(the holes), and destroying the truth of the joint, which loss is
soon discovered by the play or freedom given to the felloes allowing
them to slip out of their place. But it must be borne in mind that
this defect is just as liable to take place in felloes put together
in the other way if the holes are not truly bored, and the joints are
not well fitted.
The following directions as to putting on the tires are given in the
“Coachmaker’s Handbook,” an American work:—
“First examine the wheels and see what condition they are in for the
tire, so that we can determine what draught to give them. See if the
felloes are drawn snug on the shoulder of the spokes, and how much
open there is in the rim; for instance, one set we will suppose to
be 1½-inch felloe, open ³⁄₁₆ of an inch, give a good ¼-inch draught;
1⅜-inch felloe, ³⁄₁₆ open, just ¼-inch draught; 1¼-inch felloe, ³⁄₁₆
open, ³⁄₁₆-draught, and so on.
“Now in determining what draught to give the above wheels, we
supposed them all to be good, sound, hard, hickory felloes; if the
felloes are of soft timber just give them a trifle more draught. If
the wheels should be above ¼-inch dish, the felloes would want only
one-half the opening, but give them the same draught as the above. In
running the tire, lay all the above tire in sets on the floor, roll
the wheels on them, and allow 1 inch for taking up in bending; then
mark the end of the nave with chalk, 1, 2, 3, 4, &c., and the tire
with a sharp cold chisel mark I., II., III., IV., &c. Then straighten
on a block set up endwise about 2 feet high, a little concave or
hollow in the centre, letting the helper strike while the smith
manages the tires until the kinks are all taken out of them. Then
bend one end a little, so that it can be got into the machine, and
take pains to get them as round as possible.
“In running the wheels with a ‘traveller,’ a wedge must be driven in
one of the joints of the felloe for the purpose of tightening the
other joints in the rim. Then get the length of the felloe, and in
running the tire cut it ⅛ inch shorter than the rim measures. In this
explanation we are supposed to have steel tire, and we have a kind
of steel tire now that is very high and difficult to weld, and there
are many smiths that will profit by this lesson if they attend to the
precaution we give. This tire steel will not stand as heavy heat as
even cast steel, and if it is over-heated in the least it will crack
or break in two while hot.
“There is one peculiar fact connected with it that we find in no
other kind of steel, and that is this: it is apt to slip, however
good the heat, and to obviate this, after scaffing the ends down
to a sharp edge, make a rather sharp lap, and while hot take a
sharp-pointed punch and punch a hole nearly through both laps, and
drive in a sharp pin made of ³⁄₁₆-inch steel wire and ½ inch long.
This will not show on the outside of the tire when on the wheel,
neither does it weaken the tire like a rivet. We have often seen
tires broken where the rivet went through.
“In welding, first have your fire perfectly clean, the coal pretty
well charred, and the fire hot, but rather small, for the smaller the
fire, if hot, the less it will waste your tire each side of the weld;
have the borax charred; put a little on the weld while hot, pull the
fire open with the poker and place the lap in the hottest part; roll
a few pieces of coked coal on the weld, blow steadily, carrying your
tire back and forward through the fire, or stop the blast a moment
until the lap is heated alike all through; take it out and weld with
hammer and sledge. With this precaution you will never fail getting
a good welding heat, and need not upset your tire before welding. If
your tire is upset before welding it makes the lap so much thicker
that before it can be heated through alike there is a liability to
over-heat, and waste away the tire on each side of the weld.
“In laying the tires down the heaviest should be laid at the bottom,
and levelled with brick, so that the tire will rest permanently on
every brick or bearing, and the rest laid on top the way they will
fit best, to prevent warping the tire in the fire. A level stone
should be used to lay the wheel on when the tire is put on. If the
tires do not get warped in the fire do not hammer them at all,
without there are some kinks left in the tires in fitting them; avoid
hammering if possible, for it marks the tire; cool off, gradually
pouring the water on out of the spout of a tea-kettle until it
shrinks enough so it can be taken up; then roll it in soap-water
to prevent it from hardening, until it is so cool that it will not
burn the felloes, truing up while the helper is rolling it in the
water with a mallet covered with thick leather at both ends; let
the third person take the wheel and finish truing the tire with a
leather-covered mallet; while it is so hot that you cannot bear your
hand on it the felloes move easily under the tire, and it should not
be moved after it has cooled off if it can be otherwise avoided,
for this reason, when the tire gets cold all its roughness and
imperfections become embedded in the felloe.”
“The tire once moved will move the easier next time. After the tires
are all on examine the wheels, and see if there are any crooked spots
in the tire that do not set down to the rim; should there be any,
heat a short piece of iron and lay on the tire, it will soon heat
it enough to burn the felloe, but take it off before that time, and
rap it down with a hammer. It is a bad practice to heat the tires on
a forge as some do, for in truing them in fitting we have to bend
them cold, and if heated on the forge and one place red hot, you
will often find there a short crook edgewise. If some of the wheels
are dished more than the others, put them on the off-side of the
carriage. Never take a tire off if it can be avoided, without it is
so loose or tight as to spoil the wheel when run.”
When the tire has got sufficiently cold it is riveted to the felloe
by countersunk rivets, one on each side of the felloe joints.
The strength or weakness of wheels plays an important part in the
durability of the vehicle, for in whatever manner the various forces
are mechanically met they at last concentrate themselves on the
wheel; it is highly necessary, therefore, that great pains should
be taken in constructing them. The stock is not necessarily the
foundation on which to build a wheel, and, further, there are many
objections to its being so constituted. In the first place, when
its centre is all scooped out for the reception of the axle-box,
and its sides are mortised out to receive the ends of the spokes,
it is nothing but a mere shell. Every mortise hole is more or less
a receptacle for water, which the best workmanship cannot wholly
exclude; and as one part of the stock is always more porous than
another, that is the part that will soonest absorb wet and begin
to decay. If, therefore, the stock could be dispensed with greater
durability would be insured.
[Illustration: Fig. 16.]
[Illustration: Fig. 17.]
A thoughtful inventor, turning over these things in his mind, has,
during the last few years, produced a wheel of novel construction,
which is found practically to be superior to the one in common use.
All the spokes, instead of being shouldered down to enter the stock,
are made wedge-shaped at the end, and instead of the wheel being
constructed from the centre to the felloe, it is constructed from the
felloe to the centre. Every felloe is made and fitted with its two
spokes, which, as they converge towards the centre, press upon each
other in such a manner that when the whole periphery is put together
a solid centre is produced by the spokes themselves, as shown in
Figs. 16 and 17; so that instead of being dependent on wooden stocks
the spokes are dependent upon each other, and by being tightly wedged
together create a mutual support and resistance. The whole are
secured by two metal flanges, one at the back and one at the front of
the centre of the wheel, which are tightly screwed up, by which means
the greatest amount of solidity is obtained for the entire structure
of the wheel.
This invention is due to the Messrs. McNeile Brothers, of the
Patent Steam Wheel and Axle Company, and it is a significant fact
that wheels similarly constructed have for a considerable time been
adopted by the Royal Artillery; moreover, they have been extensively
used on street cabs, heavy carts, more particularly the latter,
and have invariably maintained their character for superiority.
For ourselves, we can see that a wheel so constructed must possess
peculiar advantages. There is no stock to rot, and the wheel cannot
in any sense be spoke-bound, as is frequently the case with wheels
of ordinary construction, by the mortise in the stock and the bore
in the felloe not ranging in a true line with the spoke. In the
growing desire to produce wheels of light construction, great efforts
have been made to reduce the size of the centre, and the inventors
of these wheels have been very successful in obtaining this object.
At the centre their wheels are exceedingly light and ornamental in
appearance, and to render them still more uniform they have shortened
the arm of their axles, and consequently curtailed the length of
the axle-box, so that there is the smallest possible projection at
the centre of the wheel. At the same time all the advantages and
peculiarities of Collinge’s principle are retained. In the ordinary
Collinge axle the bearing is not upon the whole length of the arm,
and practically speaking Messrs. McNeile have in their axles cut out
all that part which is useless in this respect, so that although
their axle-arm is considerably shorter, the bearing is the same as in
the Collinge axle of ordinary construction.
One of the greatest disadvantages in the manufacture of wheels is the
want of uniformity between one another. Scarcely any two wheels are
alike. Scarcely any spokes in a wheel radiate alike; some are as much
as an inch apart more than others at the felloe; and as the shrinking
of the tire varies, some wheels, as a consequence, get more dish
than others, the spokes either compressing in the nave mortises, or
yielding by elasticity in the direction of their length. To get them
at all accurate, it is necessary to employ very skilful workmen, and
as skilful workmen are not so numerous as they might be, the cost of
wheels is very much increased. Another disadvantage attends them: a
workman may put his work badly together, and there is no means of
detecting it till the wheel is in actual use. A badly framed wheel
will show as well to the eye as a good one, and until it breaks down,
no one, whether maker or customer, can detect the inaccuracy. Unless
the master watches every wheel while the spokes are driving he can
only depend on the good faith of his workmen.
There is no remedy for this evil except substituting machines for
men’s hands. The machine, if it cuts true once, will cut true always.
Every piece of wood in a wheel ought to be shaped by machinery. The
felloes should be sawn to their exact size, curve, and length by
machine saws; they should be bored by machine augurs, and rounded by
machine shavers. The spokes should be tenoned by machine saws, and
shaped by machine lathes. The naves should be cut by a machine lathe,
and the mortises in the same cut by a machine chisel. The spokes
should not be driven in by the irregular strokes of a mallet, but
be forced into their places by the regular pressure of a machine.
And when the tire is put on the wheel should be fixed in a frame,
in order to preserve an exact size and shape. When all these things
are done, we may hope to procure wooden wheels alike in form and
quality, and moreover, accurately circular, which very often they
are not at present. All the machines should be worked by a steam
engine. There is scarcely any article of manufacture for which there
is so large a demand, and there is no great variation in their mode
of construction. Coachmakers generally seem to cling to the old
traditions of their craft with great tenacity; possibly they think
it savours of sacrilege to let progress enter their workshops too
rapidly.
The above remarks may be qualified by stating that some of the
largest manufacturers have introduced machinery, generally, into
the departments in which it is applicable, and more particularly
in the wheelwrights’ department. Some years since Messrs. Holmes,
of Derby, had mechanical appliances worked by steam power for the
following purposes:—Cutting tenons on the spokes, squaring the ends
of the felloes, also regulating their length according to the size
of wheel required; a narrow upright saw for cutting curved timber;
machine for cutting felloes of the required size and curve; machine
for boring felloes for the ends of spokes, and many other appliances
for lightening hand-labour and insuring greater accuracy in the
manufacture. But workshops filled up in this way are not yet the
rule, though their number is increasing, and so are the inventions
for application of mechanical power to the various processes.
It seems rather paradoxical to state that the dished or conical wheel
is the strongest. But the fact is, its strength arises from the
solid hoop-tyre; with a strake tyre the upright wheel would be the
strongest. When running, the great lateral strain on the wheel is
from the outside. Consequently, if the wheel be dished in an opposite
direction, the thrust will be in the direction of the greatest
resistance. The spokes cannot yield, because in yielding they would
increase the area of the circle, and this the tyre will not permit.
Upon the same principle in carpentry, which constitutes the curved or
cambered beam the strongest, the dished wheel is stronger than the
straight one.
[Illustration: Fig. 18.]
[Illustration: Fig. 19.]
Here is one very important item which must not be overlooked in the
wheelwright department, and that is, the size of the axle-box. The
axle-box is a lining of cast iron, on which the axle-arm takes its
bearing. Two forms of these are given in Figs. 18 and 19.
[Illustration: Fig. 20.]
Fig. 20 shows an improved form of stock. It will be seen it is to
be applied to straight wheels, and requires no further description
beyond noting that the stock is not weakened so much as in the
ordinary way by mortising, an iron band, A, circumscribing the nave
and forming a hold for the spokes.
Wheels should be made with a sufficient number of spokes to properly
divide the space at the felloes, and afford sufficient support to
prevent sinking in between the spokes, and at the same time avoid too
many to weaken the stock. The less the number of spokes, the stronger
the hub and the weaker the felloe. Judgment should be used in
dividing the difference, so as to make each part of the wheel strong
in proportion.