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 [68], 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 [69] 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 [70] 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.
