On Contriving Machinery





318. The power of inventing mechanical contrivances, and of

combining machinery, does not appear, if we may judge from the

frequency of its occurrence, to be a difficult or a rare gift. Of

the vast multitude of inventions which have been produced almost

daily for a series of years, a large part has failed from the

imperfect nature of the first trials; whilst a still larger

portion, which had escaped the mechanical difficulties, failed

only because the economy of their operations was not sufficiently

attended to.



The commissioners appointed to examine into the methods

proposed for preventing the forgery of bank-notes, state in their

report, that out of one hundred and seventy-eight projects

communicated to the bank and to the commissioners, there were

only twelve of superior skill, and nine which it was necessary

more particularly to examine.



319. It is however a curious circumstance, that although the

power of combining machinery is so common, yet the more beautiful

combinations are exceedingly rare. Those which command our

admiration equally by the perfection of their effects and the

simplicity of their means, are found only amongst the happiest

productions of genius.



To produce movements even of a complicated kind is not

difficult. There exist a great multitude of known contrivances

for all the more usual purposes, and if the exertion of moderate

power is the end of the mechanism to be contrived, it is possible

to construct the whole machine upon paper, and to judge of the

proper strength to be given to each part as well as to the

framework which supports it, and also of its ultimate effect,

long before a single part of it has been executed. In fact, all

the contrivance, and all the improvements, ought first to be

represented in the drawings.



320. On the other hand, there are effects dependent upon

physical or chemical properties for the determination of which no

drawings will be of any use. These are the legitimate objects of

direct trial. For example; if the ultimate result of an engine is

to be that it shall impress letters on a copperplate by means of

steel punches forced into it, all the mechanism by which the

punches and the copper are to be moved at stated intervals, and

brought into contact, is within the province of drawing, and the

machinery may be arranged entirely upon paper. But a doubt may

reasonably spring up, whether the bur that will be raised round

the letter, which has been already punched upon the copper, may

not interfere with the proper action of the punch for the letter

which is to be punched next adjacent to it. It may also be feared

that the effect of punching the second letter, if it be

sufficiently near to the first, may distort the form of that

first figure. If neither of these evils should arise, still the

bur produced by the punching might be expected to interfere with

the goodness of the impression produced by the copperplate; and

the plate itself, after having all but its edge covered with

figures, might change its form, from the unequal condensation

which it must suffer in this process, so as to render it very

difficult to take impressions from it at all. It is impossible by

any drawings to solve difficulties such as these, experiment

alone can determine their effect. Such experiments having been

made, it is found that if the sides of the steel punch are nearly

at right angles to the face of the letter, the bur produced is

very inconsiderable; that at the depth which is sufficient for

copperplate printing, no distortion of the adjacent letters takes

place, although those letters are placed very close to each

other; that the small bur which arises may easily be scraped off;

and that the copperplate is not distorted by the condensation of

the metal in punching, but is perfectly fit to print from, after

it has undergone that process.



321. The next stage in the progress of an invention, after

the drawings are finished and the preliminary experiments have

been made, if any such should be requisite, is the execution of

the machine itself. It can never be too strongly impressed upon

the minds of those who are devising new machines, that to make

the most perfect drawings of every part tends essentially both to

the success of the trial, and to economy in arriving at the

result. The actual execution from working drawings is

comparatively an easy task; provided always that good tools are

employed, and that methods of working are adopted, in which the

perfection of the part constructed depends less on the personal

skill of the workman, than upon the certainty of the method

employed.



322. The causes of failure in this stage most frequently

derive their origin from errors in the preceding one; and it is

sufficient merely to indicate a few of their sources. They

frequently arise from having neglected to take into consideration

that metals are not perfectly rigid but elastic. A steel cylinder

of small diameter must not be regarded as an inflexible rod; but

in order to ensure its perfect action as an axis, it must be

supported at proper intervals.



Again, the strength and stiffness of the framing which

supports the mechanism must be carefully attended to. It should

always be recollected, that the addition of superfluous matter to

the immovable parts of a machine produces no additional momentum,

and therefore is not accompanied with the same evil that arises

when the moving parts are increased in weight. The stiffness of

the framing in a machine produces an important advantage. If the

bearings of the axis (those places at which they are supported)

are once placed in a straight line, they will remain so, if the

framing be immovable; whereas if the framework changes its form,

though ever so slightly, considerable friction is immediately

produced. This effect is so well understood in the districts

where spinning factories are numerous, that, in estimating the

expense of working a new factory, it is allowed that five per

cent on the power of the steam-engine will be saved if the

building is fireproof: for the greater strength and rigidity of a

fireproof building prevents the movement of the long shafts or

axes which drive the machinery, from being impeded by the

friction that would arise from the slightest deviation in any of

the bearings.



323. In conducting experiments upon machinery, it is quite a

mistake to suppose that any imperfect mechanical work is good

enough for such a purpose. If the experiment is worth making, it

ought to be tried with all the advantages of which the state of

mechanical art admits; for an imperfect trial may cause an idea

to be given up, which better workmanship might have proved to be

practicable. On the other hand, when once the efficiency of a

contrivance has been established, with good workmanship it will

be easy afterwards to ascertain the degree of perfection which

will suffice for its due action.



324. It is partly owing to the imperfection of the original

trials, and partly to the gradual improvements in the art of

making machinery, that many inventions which have been tried, and

given up in one state of art, have at another period been

eminently successful. The idea of printing by means of moveable

types had probably suggested itself to the imagination of many

persons conversant with impressions taken either from blocks or

seals. We find amongst the instruments discovered in the remains

of Pompeii and Herculaneum, stamps for words formed out of one

piece of metal, and including several letters. The idea of

separating these letters, and of recombining them into other

words, for the purpose of stamping a book, could scarcely have

failed to occur to many: but it would almost certainly have been

rejected by those best acquainted with the mechanical arts of

that time; for the workmen of those days must have instantly

perceived the impossibility of producing many thousand pieces of

wood or metal, fitting so perfectly and ranging so uniformly, as

the types or blocks of wood now used in the art of printing.



The principle of the press which bears the name of Bramah,

was known about a century and a half before the machine, to which

it gave rise, existed; but the imperfect state of mechanical art

in the time of the discoverer, would have effectually deterred

him, if the application of it had occurred to his mind, from

attempting to employ it in practice as an instrument for exerting

force.



These considerations prove the propriety of repeating, at the

termination of intervals during which the art of making machinery

has received any great improvement, the trails of methods which,

although founded upon just principles, had previously failed.



325. When the drawings of a machine have been properly made,

and the parts have been well executed, and even when the work it

produces possesses all the qualities which were anticipated,

still the invention may fail; that is, it may fail of being

brought into general practice. This will most frequently arise

from the circumstance of its producing its work at a greater

expense than that at which it can be made by other methods.



326. Whenever the new, or improved machine, is intended to

become the basis of a manufacture, it is essentially requisite

that the whole expense attending its operations should be fully

considered before its construction is undertaken. It is almost

always very difficult to make this estimate of the expense: the

more complicated the mechanism, the less easy is the task; and in

cases of great complexity and extent of machinery it is almost

impossible. It has been estimated roughly, that the first

individual of any newly invented machine, will cost about five

times as much as the construction of the second, an estimate

which is, perhaps, sufficiently near the truth. If the second

machine is to be precisely like the first, the same drawings, and

the same patterns will answer for it; but if, as usually happens,

some improvements have been suggested by the experience of the

first, these must be more or less altered. When, however, two or

three machines have been completed, and many more are wanted,

they can usually be produced at much less than one-fifth of the

expense of the original invention.



327. The arts of contriving, of drawing, and of executing, do

not usually reside in their greatest perfection in one

individual; and in this, as in other arts, the division of labour

must be applied. The best advice which can be offered to a

projector of any mechanical invention, is to employ a respectable

draughtsman; who, if he has had a large experience in his

profession, will assist in finding out whether the contrivance is

new, and can then make working drawings of it. The first step,

however, the ascertaining whether the contrivance has the merit

of novelty, is most important; for it is a maxim equally just in

all the arts, and in every science, that the man who aspires to

fortune or to fame by new discoveries, must be content to examine

with care the knowledge of his contemporaries, or to exhaust his

efforts in inventing again, what he will most probably find has

been better executed before.



328. This, nevertheless, is a subject upon which even

ingenious men are often singularly negligent. There is, perhaps,

no trade or profession existing in which there is so much

quackery, so much ignorance of the scientific principles, and of

the history of their own art, with respect to its resources and

extent, as are to be met with amongst mechanical projectors. The

self-constituted engineer, dazzled with the beauty of some,

perhaps, really original contrivance, assumes his new profession

with as little suspicion that previous instruction, that thought

and painful labour, are necessary to its successful exercise, as

does the statesman or the senator. Much of this false confidence

arises from the improper estimate which is entertained of the

difficulty of invention in mechanics. It is, therefore, of great

importance to the individuals and to the families of those who

are too often led away from more suitable pursuits, the dupes of

their own ingenuity and of the popular voice, to convince both

them and the public that the power of making new mechanical

combinations is a possession common to a multitude of minds, and

that the talents which it requires are by no means of the highest

order. It is still more important that they should be impressed

with the conviction that the great merit, and the great success

of those who have attained to eminence in such matters, was

almost entirely due to the unremitted perseverance with which

they concentrated upon their successful inventions the skill and

knowledge which years of study had matured.





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