_MACHINE COMBINATION._
The combination of several functions in one machine, although
it may not seem an important matter to be considered here, is
nevertheless one that has much to do with the manufacture of
machines, and constitutes what may be termed a principle of
construction.
The reasons that favour combination of functions in machines, and
the effects that such combinations may produce, are so various that
the problem has led to a great diversity of opinions and practice
among both those who construct and even those who employ machines.
It may be said, too, that a great share of the combinations found
in machines, such as those to turn, mill, bore, slot, and drill in
iron fitting, are not due to any deliberate plan on the part of
the makers, so much as to an opinion that such machines represent
a double or increased capacity. So far has combination in machines
been carried, that in one case that came under the writer's
notice, a machine was arranged to perform nearly every operation
required in finishing the parts of machinery; completely organised,
and displaying a high order of mechanical ability in design and
arrangement, but practically of no more value than a single machine
tool, because but one operation at a time could be performed.
To direct the attention of learners to certain rules that
will guide them in forming opinions in this matter of machine
combination, I will present the following propositions, and
afterwards consider them more in detail:--
_First._ By combining two or more operations in one machine, the
only objects gained are a slight saving in first cost, one frame
answering for two or more machines, and a saving of floor room.
_Second._ In a machine where two or more operations are combined,
the capacity of such a machine is only as a single one of these
operations, unless more than one can be carried on at the same time
without interfering one with another.
_Third._ Combination machines can only be employed with success
when one attendant performs all the operations, and when the
change from one to another requires but little adjustment and
re-arrangement.
_Fourth._ The arrangement of the parts of a combination machine
have to be modified by the relations between them, instead of being
adapted directly to the work to be performed.
_Fifth._ The cost of special adaptation, and the usual
inconvenience of fitting combination machines when their parts
operate independently, often equals and sometimes exceeds what is
saved in framing and floor space.
Referring first to the saving effected by combining several
operations in one machine, there is perhaps not one constructor
in twenty that ever stops to consider what is really gained, and
perhaps not one purchaser in a hundred that does the same thing.
The impression is, that when one machine performs two operations it
saves a second machine. A remarkable example of this exists in the
manufacture of combination machines in Europe for working wood,
where it is common to find complicated machines that will perform
all the operations of a joiner's shop, but as a rule only one thing
at a time, and usually in an inconvenient manner, each operation
being hampered and interfered with by another; and in changing from
one kind of work to another the adjustments and changes generally
equal and sometimes exceed the work to be done. What is stranger
still is, that such machines are purchased, when their cost often
equals that of separate machines to perform the same work.
In metal working, owing to a more perfect division of labour, and a
more intelligent manipulation than in wood-working, there is less
combination in machines--in fact, a combination machine for metal
work is rarely seen at this day, and never under circumstances
where it occasions actual loss. The advantage of combination, as
said, can only be in the framing and floor space occupied by the
machines, but these considerations, to be estimated by a proper
standard, are quite insignificant when compared with other items in
the cost of machine operating, such as the attendance, interest on
the invested cost of the machine, depreciation of value by wear,
repairing, and so on.
Assuming, for example, that a machine will cost as much as the
wages of an attendant for one year, which is not far from an
average estimate for iron working machine tools, and that interest,
wear, and repairs amount to ten per cent. on this sum, then the
attendance would cost ten times as much as the machine; in other
words, the wages paid to a workman to attend a machine is, on an
average, ten times as much as the other expenses attending its
operation, power excepted. This assumed, it follows that in machine
tools any improvement directed to labour saving is worth _ten
times_ as much as an equal improvement directed to the economy of
first cost.
This mode of reasoning will lead to proper estimates of the
difference in value between good tools and inferior tools; the
results of performance instead of the investment being first
considered, because the expenses of operating are, as before
assumed, usually ten times as great as the interest on the value of
a machine.
In view of these propositions, I need hardly say to what object
machine improvements should be directed, nor which of the
considerations named are most affected by a combination of machine
functions; the fact is, that if estimates could be prepared,
showing the actual effect of machine combinations, it would
astonish those who have not investigated the matter, and in many
cases show a loss of the whole cost of such machines each year. The
effect of combination machines is, however, by no means uniform;
the remarks made apply to standard machines employed in the regular
work of an engineering or other establishment. In exceptional cases
it may be expedient to use combined machines. In the tool-room of
machine-shops, for instance, where one man can usually perform the
main part of the work, and where there is but little space for
machines, the conditions are especially favourable to combination
machines, such as may be used in milling, turning, drilling, and so
on; but wherever there is a necessity or an opportunity to carry
on two or more of these operations at the same time, the cost of
separate machines is but a small consideration when compared with
the saving of labour that may be effected by independent tools to
perform each operation. The tendency of manufacturing processes
of every kind, at this time, is to a division of labour, and to a
separation of each operation into as many branches as possible, so
that study spent in "segregating" instead of "aggregating" machine
functions is most likely to produce profitable results.
This article has been introduced, not only to give a true
understanding of the effect and value of machine combination,
but to caution against a common error of confounding machine
combination with invention.
A great share of the alleged improvements in machinery, when
investigated will be found to consist in nothing more than the
combination of several functions in one machine, the novelty of
their arrangement leading to an impression of utility and increased
effect.
(1.) What is gained by arranging a machine to perform
several different operations?--(2.) What may be lost by such
combination?--(3.) What is the main expense attending the
operation of machine tools?--(4.) What kind of improvement in
machine tools produces the most profitable result?--(5.) What are
the principal causes which have led to machine combinations.