CHAPTER XVIII.MACHINE COMBINATION.

(1.) Why has the lifting of weights been made a standard for the measure of power?—(2.) Name some of the difficulties to contend with in the operation of machinery for lifting or handling material.—(3.) What analogy exists between manual handling and the operation of hydraulic cranes?—(4.) Explain how the employment of overhead cranes saves room in a fitting shop.—(5.) Under what circumstances is it expedient to move material vertically?—(6.) To what circumstances is the danger of handling mainly attributable?

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 complicatedmachines 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 worthten timesas 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 astonishthose 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.

The first and, perhaps, the most important matter of all in founding engineering works is that of arrangement. As a commercial consideration affecting the cost of manipulation, and the expense of handling material, the arrangement of an establishment may determine, in a large degree, the profits that may be earned, and, as explained in a previous place, upon this matter of profits depends the success of such works.

Aside from the cost or difficulty of obtaining ground sufficient to carry out plans for engineering establishments, the diversity of their arrangement met with, even in those of modern construction, is no doubt owing to a want of reasoning from general premises. There is always a strong tendency to accommodate local conditions, and not unfrequently the details of shop manipulation are quite overlooked, or are not understood by those who arrange buildings.

The similarity of the operations carried on in all works directed to the manufacture of machinery, and the kind of knowledge that is required in planning and conducting such works, would lead us to suppose that at least as much system would exist in machine shops as in other manufacturing establishments, which is certainly not the case. There is, however, this difference to be considered: that whereas many kinds of establishments can be arranged at the beginning for a specific amount of business, machine shops generally grow up around a nucleus, and are gradually extended as their reputation and the demands for their productions increase; besides, the variety of operations required in an engineering establishment, and change from one class of work to another, are apt to lead to a confusion in arrangement, which is too often promoted, or at least not prevented, by insufficient estimates of the cost of handling and moving material.

Materials consumed in an engineering establishment consist mainly of iron, fuel, sand, and lumber. These articles, or their products, during the processes of manipulation, are continually approaching the erecting shop, from which finished machineryis sent out after its completion. This constitutes the erecting shop, as a kind of focal centre of a works, which should be the base of a general plan of arrangement. This established, and the foundry, smithy, finishing, and pattern shops regarded as feeding departments to the erecting shop, it follows that the connections between the erecting shop and other departments should be as short as possible, and such as to allow free passage for material and ready communication between managers and workmen in the different rooms. These conditions would suggest a central room for erecting, with the various departments for casting, forging, and finishing, radiating from the erecting shop like the spokes of a wheel, or, what is nearly the same, branching off at right angles on either side and at one end of a hollow square, leaving the fourth side of the erecting room to front on a street or road, permitting free exit for machinery when completed.

The material when in its crude state not only consists of various things, such as iron, sand, coal, and lumber, that must be kept separate, but the bulk of such materials is much greater than their finished product. It is therefore quite natural to receive such material on the outside or "periphery" of the works where there is the most room for entrances and for the separate storing of such supplies. Such an arrangement is of course only possible where there can be access to a considerable part of the boundary of a works, yet there are but few cases where a shop cannot be arranged in general upon the plan suggested. By receiving material on the outside, and delivering the finished product from the centre, communications between the departments of an establishment are the shortest that it is possible to have; by observing the plans of the best establishments of modern arrangement, especially those in Europe, it may be seen that this system is approximated in many of them, especially in establishments devoted to the manufacture of some special class of work.

Handling and moving material is the principal matter to be considered in the arrangement of engineering works. The constructive manipulation can be watched, estimated, and faults detected by comparison, but handling, like the designs for machinery, is a more obscure matter, and may be greatly at fault without its defects being apparent to any but those who are highly skilled, and have had their attention especially directedto the matter.

Presuming an engineering establishment to consist of one-storey buildings, and the main operations to be conducted on the ground level, the only vertical lifting to be performed will be in the erecting room, where the parts of machines are assembled. This room should be reached in every part by over-head travelling cranes, that cannot only be used in turning, moving, and placing the work, but in loading it upon cars or waggons. One result of the employment of over-head travelling cranes, often overlooked, is a saving of floor-room; in ordinary fitting, from one-third more to twice the number of workmen will find room in an erecting shop if a travelling-crane is employed, the difference being that, in moving pieces they may pass over the top of other pieces instead of requiring long open passages on the floor. So marked is this saving of room effected by over-head cranes, that in England, where they are generally employed, handling is not only less expensive and quicker, but the area of erecting floors is usually one-half as much as in America, where travelling-cranes are not employed.

Castings, forgings, and general supplies for erecting can be easily brought to the erecting shop from the other departments on trucks without the aid of motive power; so that the erecting and foundry cranes will do the entire lifting duty required in any but very large establishments.

The auxiliary departments, if disposed about an erecting shop in the centre, should be so arranged that material which has to pass through two or more departments can do so in the order of the processes, and without having to cross the erecting shop. Casting, boring, planing, drilling, and fitting, for example, should follow each other, and the different departments be arranged accordingly; whenever a casting is moved twice over the same course, it shows fault of arrangement and useless expense. The same rule applies to all kinds of material.

A great share of the handling about an engineering establishment is avoided, if material can be stored and received on a higher level than the working floors; if, for instance, coal, iron, and sand is received from railway cars at an elevation sufficient to allow it to be deposited where it is stored by gravity, it is equivalent to saving the power and expense required to raise the material to such a height, or move it and pile it up, which amounts to the same thing in the end. It is not proposed to follow the detailsof shop arrangement, farther than to furnish a clue to some of the general principles that should be regarded in devising plans of arrangement. Such principles are much more to be relied upon than even experience in suggesting the arrangement of shops, because all experience must be gained in connection with special local conditions, which often warp and prejudice the judgment, and lead to error in forming plans under circumstances different from those where the experience was gained.

(1.) How may the arrangement of an establishment affect its earnings?—(2.) Why is the arrangement of engineering establishments generally irregular?—(3.) Why should an erecting shop be a base of arrangement in engineering establishments?—(4.) What are the principal materials consumed in engineering works?—(5.) Why is not special experience a safe guide in forming plans of shop arrangement?

Having thus far treated of such general principles and facts connected with practical mechanics as might properly precede, and be of use in, the study of actual manipulation in a workshop, we come next to casting, forging, and finishing, with other details that involve manual as well as mental skill, and to which the term "processes" will apply.

As these shop processes or operations are more or less connected, and run one into the other, it will be necessary at the beginning to give a short summary of them, stating the general object of each, that may serve to render the detailed remarks more intelligible to the reader as he comes to them in their consecutive order.

Designing, or generating the plans of machinery, may be considered the leading element in engineering manufactures or machine construction, that one to which all others are subordinate,both in order and importance, and is that branch to which engineering knowledge is especially directed. Designing should consist, first, in assuming certain results, and, secondly, in conceiving of mechanical agents to produce these results. It comprehends the geometry of movements, the disposition and arrangement of material, the endurance of wearing surfaces, adjustments, symmetry; in short, all the conditions of machine operation and machine construction. This subject will be again treated of at more length in another section.

Draughting, or drawing, as it is more commonly called, is a means by which mental conceptions are conveyed from one person to another; it is the language of mechanics, and takes the place of words, which are insufficient to convey mechanical ideas in an intelligible manner.

Drawings represent and explain the machinery to which they relate as the symbols in algebra represent quantities, and in a degree admit of the same modifications and experiments to which the machinery itself could be subjected if it were already constructed. Drawings are also an important aid in developing designs or conceptions. It is impossible to conceive of, and retain in the mind, all the parts of a complicated machine, and their relation to each other, without some aid to fix the various ideas as they arise, and keep them in sight for comparison; like compiling statistics, the footings must be kept at hand for reference, and to determine the relation that one thing may bear to another.

In the workshop, the objects of drawing are to communicate plans and dimensions to the workmen, and to enable a division of the labour, so that the several parts of a machine may be operated upon by different workmen at the same time—also to enable classification and estimates of cost to be made, and records kept.

Drawings are, in fact, the base of shop system, upon which depends not only the accuracy and uniformity of what is produced, but also, in a great degree, its cost. Complete drawings of whatever is made are now considered indispensable in the best regulated establishments; yet we are not so far removed from a time when most work was made without drawings, but what we may contrast the present system with that which existed but a few years ago, when to constructa new machine was a great undertaking, involving generally many experiments and mistakes.

Pattern-making relates to the construction of duplicate models for the moulded parts of machinery, and involves a knowledge of shrinkage and cooling strains, the manner of moulding and proper position of pieces, when cast, to ensure soundness in particular parts. As a branch of machine manufacture, pattern-making requires a large amount of special knowledge, and a high degree of skill; for in no other department is there so much that must be left to the discretion and judgment of workmen.

Pattern-makers have to thoroughly understand drawings, in order to reproduce them on the trestle boards with allowance for shrinkage, and to determine the cores; they must also understand moulding, casting, fitting, and finishing. Pattern-making as a branch of machine manufacture, should rank next to designing and drafting.

Founding and casting relate to forming parts of machinery by pouring melted metal into moulds, the force of gravity alone being sufficient to press or shape it into even complicated forms. As a process for shaping such metal as is not injured by the high degree of heat required in melting, moulding is the cheapest and most expeditious of all means, even for forms of regular outline, while the importance of moulding in producing irregular forms is such that without this process the whole system of machine construction would have to be changed. Founding operations are divided into two classes, known technically as green sand moulding, and loam or dry sand moulding; the first, when patterns or duplicates are used to form the moulds, and the second, when the moulds are built by hand without the aid of complete patterns. Founding involves a knowledge of mixing and melting metals such as are used in machine construction, the preparing and setting of cores for the internal displacement of the metal, cooling and shrinking strains, chills, and many other things that are more or less special, and can only be learned and understood from actual observation and practice.

Forging relates to shaping metal by compression or blows when it is in a heated and softened condition; as a process, it is an intermediate one between casting and what may be called the cold processes. Forging also relates to welding or joiningpieces together by sudden heating that melts the surface only, and then by forcing the pieces together while in this softened or semi-fused state. Forging includes, in ordinary practice, the preparation of cutting tools, and tempering them to various degrees of hardness as the nature of the work for which they are intended may require; also the construction of furnaces for heating the material, and mechanical devices for handling it when hot, with the various operations for shaping, which, as in the case of casting, can only be fully understood by experience and observation.

Finishing and fitting relates to giving true and accurate dimensions to the parts of machinery that come in contact with each other and are joined together or move upon each other, and consists in cutting away the surplus material which has to be left in founding and forging because of the heated and expanded condition in which the material is treated in these last processes. In finishing, material is operated upon at its normal temperature, in which condition it can be handled, gauged, or measured, and will retain its shape after it is fitted. Finishing comprehends all operations of cutting and abrading, such as turning, boring, planing and grinding, also the handling of material; it is considered the leading department in shop manipulation, because it is the one where the work constructed is organised and brought together. The fitting shop is also that department to which drawings especially apply, and other preparatory operations are usually made subservient to the fitting processes.

Shop system may also be classed as a branch of engineering work; it relates to the classification of machines and their parts by symbols and numbers, to records of weight, the expense of cast, forged, and finished parts, and apportions the cost of finished machinery among the different departments. Shop system also includes the maintenance of standard dimensions, the classification and cost of labour, with other matters that partake both of a mechanical and a commercial nature.

In order to render what is said of shop processes more easily understood, it will be necessary to change the order in which they have been named. Designing, and many matters connected with the operation of machines, will be more easily learned and understood after having gone through with what may be called the constructive operations, such as involve manual skill.

(1.) Name the different departments of an engineering establishment.—(2.) What does the engineering establishment include?—(3.) What does the commercial department include?—(4.) The foundry department?—(5.) The forging department?—(6.) The fitting department?—(7.) What does the term shop system mean as generally employed?

Machine-drawing may in some respects be said to bear the same relation to mechanics that writing does to literature; persons may copy manuscript, or write from dictation, of what they do not understand; or a mechanical draughtsman may make drawings of a machine he does not understand; but neither such writing or drawing can have any value beyond that of ordinary labour. It is both necessary and expected that a draughtsman shall understand all the various processes of machine construction, and be familiar with the best examples that are furnished by modern practice.

Geometrical drawing is not an artistic art so much as it is a constructive mechanical one; displaying the parts of machinery on paper, is much the same in practice, and just the same in principle, as measuring and laying out work in the shop.

Artistic drawing is addressed to the senses, geometrical drawing is addressed to the understanding. Geometrical drawing may, however, include artistic skill not in the way of ornamentation, but to convey an impression of neatness and completeness, that has by common custom been assumed among engineers, and which conveys to the mind an idea of competent construction in the drawing itself, as well as of the machinery which is represented. Artistic effect, so far as admissible in mechanical drawing, is easy to learn, and should be understood, yet through a desire to make pictures, a beginner is often led to neglect that which is more important in the way of accuracy and arrangement.

It is easy to learn "how" to draw, but it is far from easy to learn "what" to draw. Let this be kept in mind, not in the way ofdisparaging effort in learning "how" to draw, for this must come first, but in order that the objects and true nature of the work will be understood.

The engineering apprentice, as a rule, has a desire to make drawings as soon as he begins his studies or his work, and there is not the least objection to his doing so; in fact, there is a great deal gained by illustrating movements and the details of machinery at the same time of studying the principles. Drawings if made should always be finished, carefully inked in, and memoranda made on the margin of the sheets, with the date and the conditions under which the drawings were made. The sheets should be of uniform size, not too large for a portfolio, and carefully preserved, no matter how imperfect they may be. An apprentice who will preserve his first drawings in this manner will some day find himself in possession of a souvenir that no consideration would cause him to part with.

For implements procure two drawing-boards, forty-two inches long and thirty inches wide, to receive double elephant paper; have the boards plain without cleets, or ingenious devices for fastening the paper; they should be made from thoroughly seasoned lumber, at least one and one-fourth inches thick; if thinner they will not be heavy enough to resist the thrust of the T squares.

It is better to have two boards, so that one may be used for sketching and drawing details, which, if done on the same sheet with elevations, dirties the paper, and is apt to lower the standard of the finished drawing by what may be called bad association.

Details and sketches, when made on a separate sheet, should be to a larger scale than elevations. By changing from one scale to another the mind is schooled in proportion, and the conception of sizes and dimensions is more apt to follow the finished work to which the drawings relate.

In working to regular scales, such as one-half, one-eighth, or one-sixteenth size, a good plan is to use a common rule, instead of a graduated scale. There is nothing more convenient for a mechanical draughtsman than to be able to readily resolve dimensions into various scales, and the use of a common rule for fractional scales trains the mind, so that computations come naturally, and after a time almost without effort. A plain T square, with a parallel blade fastened on the side of the head,but not imbedded into it, is the best; in this way set squares can pass over the head of a T square in working at the edges of the drawing. It is strange that a draughting square should ever have been made in any other manner than this, and still more strange, that people will use squares that do not allow the set squares to pass over the heads and come near to the edge of the board.

A bevel square is often convenient, but should be an independent one; a T square that has a movable blade is not suitable for general use. Combinations in draughting instruments, no matter what their character, should be avoided; such combinations, like those in machinery, are generally mistakes, and their effect the reverse of what is intended.

For set squares, or triangles, as they are sometimes called, no material is so good as ebonite; such squares are hard, smooth, impervious to moisture, and contrast with the paper in colour; besides they wear longer than those made of wood. For instruments, it is best to avoid everything of an elaborate or fancy kind; such sets are for amateurs, not engineers. It is best to procure only such instruments at first as are really required, of the best quality, and then to add others as necessity may demand; in this way, experience will often suggest modifications of size or arrangement that will add to the convenience of a set.

One pair each of three and one-half inch and five inch compasses, two ruling pens, two pairs of spring dividers, one for pens and one for pencils, a triangular boxwood scale, a common rule, and a hard pencil, are the essential instruments for machine-drawing. At the beginning, when "scratching out" will probably form an item in the work, it is best to use Whatman's paper, or the best roll paper, which, of the best manufacture, is quite as good as any other for drawings that are not water-shaded.

In mounting sheets that are likely to be removed and replaced, for the purpose of modification, as working drawings generally are, they can be fastened very well by small copper tacks driven along the edges at intervals of two inches or less. The paper can be very slightly dampened before fastening in this manner, and if the operation is carefully performed the paper will be quite as smooth and convenient to work upon as though it were pasted down; the tacks can be driven down so as to be flush with, or below the surface of, the paper, and will offer no obstructionto squares.

If a drawing is to be elaborate, or to remain long upon a board, the paper should be pasted down. To do this, first prepare thick mucilage, or what is better, glue, and have it ready at hand, with some slips of absorbent paper an inch or so wide. Dampen the sheet on both sides with a sponge, and then apply the mucilage along the edge, for a width of one-fourth or three-eighths of an inch. It is a matter of some difficulty to place a sheet upon a board; but if the board is set on its edge, the paper can be applied without assistance. Then, by placing the strips of paper along the edge, and rubbing over them with some smooth hard instrument, the edges of the sheet can be pasted firmly to the board, the paper slips taking up a part of the moisture from the edges, which are longest in drying. If left in this condition, the centre will dry first, and the paper be pulled loose at the edges by contraction before the paste has time to dry. It is therefore necessary to pass over the centre of the sheet with a wet sponge at intervals to keep the paper slightly damp until the edges adhere firmly, when it can be left to dry, and will be tight and smooth. In this operation much will be learned by practice, and a beginner should not be discouraged by a few failures. One of the most common difficulties in mounting sheets is in not having the gum or glue thick enough; when thin, it will be absorbed by the wood or the paper, or is too long in drying; it should be as thick as it can be applied with a brush, and made from clean Arabic gum, tragacanth, or fine glue.

Thumb-tacks are of but little use in mechanical drawing except for the most temporary purposes, and may very well be dispensed with altogether; they injure the draughting-boards, obstruct the squares, and disfigure the sheets.

Pencilling is the first and the most important operation in draughting; more skill is required to produce neat pencil-work than to ink in the lines after the pencilling is done.

A beginner, unless he exercises great care in the pencil-work of a drawing, will have the disappointment to find the paper soon becoming dirty from plumbago, and the pencil-lines crossing each other everywhere, so as to give the whole a slovenly appearance. He will also, unless he understands the nature of the operations in which he is engaged, make the mistake of regarding the pencil-work as an unimportant part, insteadof constituting, as it does, the main drawing, and thereby neglect that accuracy which alone can make either a good-looking or a valuable one.

Pencil-work is indeed the main operation, the inking being merely to give distinctness and permanency to the lines. The main thing in pencilling is accuracy of dimensions and stopping the lines where they should terminate without crossing others. The best pencils only are suitable for draughting; if the plumbago is not of the best quality, the points require to be continually sharpened, and the pencil is worn away at a rate that more than makes up the difference in cost between the finer and cheaper grades of pencils, to say nothing of the effect upon a drawing.

It is common to use a flat point for draughting pencils, but a round one will often be found quite as good if the pencils are fine, and some convenience is gained by a round point for free-hand use in making rounds and fillets. A Faber pencil, that has detachable points which can be set out as they are worn away, is convenient for draughting.

For compasses, the lead points should be cylindrical, and fit into a metal sheath without paper packing or other contrivance to hold them; and if a draughtsman has instruments not arranged in this manner, he should have them changed at once, both for convenience and economy.

Ink used in drawing should always be the best that can be procured; without good ink a draughtsman is continually annoyed by an imperfect working of pens, and the washing of the lines if there is shading to be done. The quality of ink can only be determined by experiment; the perfume that it contains, or tinfoil wrappers and Chinese labels, are no indication of quality; not even the price, unless it be with some first-class house. To prepare ink, I can recommend no better plan of learning than to ask some one who understands the matter. It is better to waste a little time in preparing it slowly than to be at a continual trouble with pens, which will occur if the ink is ground too rapidly or on a rough surface. To test ink, a few lines can be drawn on the margin of a sheet, noting the shade, how the ink flows from the pen, and whether the lines are sharp; after the lines have dried, cross them with a wet brush; if they wash readily, the ink is too soft; if they resist the water for a time, and then wash tardily, the ink is good. It cannot be expected that inks soluble in water can permanently resist its action after drying;in fact, it is not desirable that drawing inks should do so, for in shading, outlines should be blended into the tints where the latter are deep, and this can only be effected by washing.

Pens will generally fill by capillary attraction; if not, they should be made wet by being dipped into water; they should not be put into the mouth to wet them, as there is danger of poison from some kinds of ink, and the habit is not a neat one.

In using ruling pens, they should be held nearly vertical, leaning just enough to prevent them from catching on the paper. Beginners have a tendency to hold pens at a low angle, and drag them on their side, but this will not produce clean sharp lines, nor allow the lines to be made near enough to the edges of square blades or set squares.

In regard to the use of the T square and set squares, no useful rules can be given except to observe others, and experiment until convenient customs are attained. A beginner should be careful of adopting unusual plans, and above all things, of making important discoveries as to new plans of using instruments, assuming that common practice is all wrong, and that it is left for him to develop the true and proper way of drawing. This is a kind of discovery which is very apt to intrude itself at the beginning of an apprentice's course in many matters besides drawing, and often leads him to do and say many things which he will afterwards wish to recall.

It is generally a safe rule to assume that any custom long and uniformly followed by intelligent people is right; and, in the absence of that experimental knowledge which alone enables one to judge, it is safe to receive such customs, at least for a time, as being correct.

Without any wish to discourage the ambition of an apprentice to invent, which always inspires him to laudable exertion, it is nevertheless best to caution him against innovations. The estimate formed of our abilities is very apt to be inversely as our experience, and old engineers are not nearly so confident in their deductions and plans as beginners are.

A drawing being inked in, the next things are tints, dimension, and centre lines. The centre lines should be in red ink, and pass through all points of the drawing that have an axial centre, or where the work is similar and balanced on each side of the line. This rule is a little obscure, but will be best understood if studied in connection with a drawing, and perhaps as wellremembered without further explanation.

Dimension lines should be in blue, but may be in red. Where to put them is a great point in draughting. To know where dimensions are required involves a knowledge of fitting and pattern-making, and cannot well be explained; it must be learned in practice. The lines should be fine and clear, leaving a space in their centre for figures when there is room. The distribution of centre lines and dimensions over a drawing must be carefully studied, for the double purpose of giving it a good appearance and to avoid confusion. Figures should be made like printed numerals; they are much better understood by the workman, look more artistic, and when once learned require but little if any more time than written figures. If the scale employed is feet and inches, dimensions to three feet should be in inches, and above this in feet and inches; this corresponds to shop custom, and is more comprehensive to the workman, however wrong it may be according to other standards.

In sketches and drawings made for practice, such as are not intended for the shop, it is suggested that metrical scales be employed; it will not interfere with feet and inches, and will prepare the mind for the introduction of this system of lineal measurement, which may in time be adopted in England and America, as it has been in many other countries.

In shading drawings, be careful not to use too deep tints, and to put the shades in the right place. Many will contend, and not without good reasons, that working drawings require no shading; yet it will do no harm to learn how and where they can be shaded: it is better to omit the shading from choice than from necessity. Sections must, of course, be shaded—not with lines, although I fear to attack so old a custom, yet it is certainly a tedious and useless one: sections with light ink shading of different colours, to indicate the kind of material, are easier to make, and look much better. By the judicious arrangement of a drawing, a large share of it may be in sections, which in almost every case are the best views to work by. The proper colouring of sections gives a good appearance to a drawing, and conveys an idea of an organised machine, or, to use the shop term, "stands out from the paper." In shading sections, leave a margin of white between the tints and the lines on the upper and left-hand sides of the section: this breaks the connection or sameness, and the effect is striking; it separates the parts,and adds greatly to the clearness and general appearance of a drawing.

Cylindrical parts in the plane of sections, such as shafts and bolts, should be drawn full, and have a 'round shade,' which relieves the flat appearance—a point to be avoided as much as possible in sectional views.

Conventional custom has assigned blue as a tint for wrought iron, neutral or pale pink for cast iron, and purple for steel. Wood is generally distinguished by "graining," which is easily done, and looks well.

The title of a drawing is a feature that has much to do with its appearance, and the impression conveyed to the mind of an observer. While it can add nothing to the real value of a drawing, it is so easy to make plain letters, that the apprentice is urged to learn this as soon as he begins to draw; not to make fancy letters, nor indeed any kind except plain block letters, which can be rapidly laid out and finished, and consequently employed to a greater extent. By drawing six parallel lines, making five spaces, and then crossing them with equidistant lines, the points and angles in block letters are determined; after a little practice, it becomes the work of but a few minutes to put down a title or other matter on a drawing so that it can be seen and read at a glance in searching for sheets or details.

In the manufacture of machines, there are usually so many sizes and modifications, that drawings should assist and determine in a large degree the completeness of classification and record. Taking the manufacture of machine tools, for example: we cannot well say, each time they are to be spoken of, a thirty-six inch lathe without screw and gearing, a thirty-two inch lathe with screw and gearing, a forty-inch lathe triple geared or double geared, with a twenty or thirty foot frame, and so on. To avoid this it is necessary to assume symbols for machines of different classes, consisting generally of the letters of the alphabet, qualified by a single number as an exponent to designate capacity or different modifications. Assuming, in the case of engine lathes, A to be the symbol for lathes of all sizes, then those of different capacity and modification can be represented in the drawings and records as A1, A2, A3, A4, and so on, requiring but two characters to indicate a lathe of any kind. These symbols should be marked in large plain letters on the left-hand lower corner of sheets, so that the manager, workman, or any one else, can see at a glance what thedrawings relate to. This symbol should run through the time-book, cost account, sales record, and be the technical name for machines to which it applies; in this way machines will always be spoken of in the works by the name of their symbol.

In making up the time charged to different machines during their construction, a good plan is to supply each workman with a slate and pencil, on which he can enter his time as so many hours or fractions of hours charged to the respective symbols. Instead of interfering with his time, this will increase a workman's interest in what he is doing, and naturally lead to a desire to diminish the time charged to the various symbols. This system leads to emulation among workmen where any operation is repeated by different persons, and creates an interest in classification which workmen will willingly assist in.

When the dimensions and symbols are added to a drawing, the next thing is pattern or catalogue numbers. These should be marked in prominent, plain figures on each piece of casting, either in red or other colour that will contrast with the general face of the drawing. These numbers, to avoid the use of symbols in connection with them, must include consecutively all patterns employed in the business, and can extend to thousands without inconvenience.

A book containing the pattern record should be kept, in which these catalogue numbers are set down, with a short description to identify the different parts to which the numbers belong, so that all the various details of any machine can at any time be referred to. Besides this description, there should be opposite the catalogue of pattern numbers, ruled spaces, in which to enter the weight of castings, the cost of the pattern, and also the amount of turned, planed, or bored surface on each piece when it is finished, or the time required in fitting, which is the same thing. In this book the assembled parts of each machine should be set down in a separate list, so that orders for castings can be made from the list without other references. This system is the best one known to the writer, and is in substance a plan now adopted in many of the best engineering establishments. A complete system in all things pertaining to drawings and classifications should be rigidly adhered to; any plan is better than none, and the schooling of the mind to be had in the observance of systematic rules is a matter not to be neglected. New plans for promoting system may at any time arise, but such plans cannot be at anytime understood and adopted except by those who have cultivated a taste for order and regularity.

In regard to shaded elevations, it may be said that photography has superseded them for the purpose of illustrating completed machines, and but few establishments care to incur the expense of ink-shaded elevations. Shaded elevations cannot be made with various degrees of care, and in a longer or shorter time; there is but one standard for them, and that is that such drawings should be made with great care and skill. Imperfect shaded elevations, although they may surprise and please the unskilled, are execrable in the eyes of a draughtsman or an engineer; and as the making of shaded elevations can be of but little assistance to an apprentice draughtsman, it is better to save the time that must be spent in order to make such drawings, and apply the same study and time to other matters of greater importance.

It is not assumed that shaded elevations should not be made, nor that ink shading should not be learned, but it is thought best to point out the greater importance of other kinds of drawing, too often neglected to gratify a taste for picture-making, which has but little to do with practical mechanics.

Isometrical perspective is often useful in drawing, especially in wood structures, when the material is of rectangular section, and disposed at right angles, as in machine frames. One isometrical view, which can be made nearly as quickly as a true elevation, will show all the parts, and may be figured for dimensions the same as plane views. True perspective, although rarely necessary in mechanical drawing, may be studied with advantage in connection with geometry; it will often lead to the explanation of problems in isometric drawing, and will also assist in free-hand lines that have sometimes to be made to show parts of machinery oblique to the regular planes. Thus far the remarks on draughting have been confined to manipulation mainly. As a branch of engineering work, draughting must depend mainly on special knowledge, and is not capable of being learned or practised upon general principles or rules. It is therefore impossible to give a learner much aid by searching after principles to guide him; the few propositions that follow comprehend nearly all that may be explained in words.

1. Geometrical drawings consist in plans, elevations, and sections; plans being views on the top of the object in a horizontal plane; elevations, views on the sides of the object in verticalplanes; and sections, views taken on bisecting planes, at any angle through an object.

2. Drawings in true elevation or in section are based upon flat planes, and give dimensions parallel to the planes in which the views are taken.

3. Two elevations taken at right angles to each other, fix all points, and give all dimensions of parts that have their axis parallel to the planes on which the views are taken; but when a machine is complex, or when several parts lie in the same plane, three and sometimes four views are required to display all the parts in a comprehensive manner.

4. Mechanical drawings should be made with reference to all the processes that are required in the construction of the work, and the drawings should be responsible, not only for dimensions, but for unnecessary expense in fitting, forging, pattern-making, moulding, and so on.

5. Every part laid down has something to govern it that may be termed a "base"—some condition of function or position which, if understood, will suggest size, shape, and relation to other parts. By searching after a base for each and every part and detail, the draughtsman proceeds upon a regular system, continually maintaining a test of what is done. Every wheel, shaft, screw or piece of framing should be made with a clear view of the functions it has to fill, and there are, as before said, always reasons why such parts should be of a certain size, have such a speed of movement, or a certain amount of bearing surface, and so on. These reasons or conditions may be classed asexpedient,important, oressential, and must be estimated accordingly. As claimed at the beginning, the designs of machines can only in a limited degree be determined by mathematical data. Leaving out all considerations of machine operation with which books have scarcely attempted to deal, we have only to refer to the element of strains to verify the general truth of the proposition.

Examining machines made by the best designers, it will be found that their dimensions bear but little if any reference to calculated strains, especially in machines involving rapid motion. Accidents destroy constants, and a draughtsman or designer who does not combine special and experimental knowledge with what he may learn from general sources, will find his services tobe of but little value in actual practice.

I now come to note a matter in connection with draughting to which the attention of learners is earnestly called, and which, if neglected, all else will be useless. I allude to indigestion, and its resultant evils. All sedentary pursuits more or less give rise to this trouble, but none of them so much as draughting. Every condition to promote this derangement exists. When the muscles are at rest, circulation is slow, the mind is intensely occupied, robbing the stomach of its blood and vitality, and, worse than all, the mechanical action of the stomach is usually arrested by leaning over the edge of a board. It is regretted that no good rule can be given to avoid this danger. One who understands the evil may in a degree avert it by applying some of the logic which has been recommended in the study of mechanics. If anything tends to induce indigestion, its opposite tends the other way, and may arrest it; if stooping over a board interferes with the action of the digestive organs, leaning back does the opposite; it is therefore best to have a desk as high as possible, stand when at work, and cultivate a constant habit of straightening up and throwing the shoulders back, and if possible, take brief intervals of vigorous exercise. Like rating the horse-power of a steam-engine, by multiplying the force into the velocity, the capacity of a man can be estimated by multiplying his mental acquirements into his vitality.

Physical strength, bone and muscle, must be elements in successful engineering experience; and if these things are not acquired at the same time with a mechanical education, it will be found, when ready to enter upon a course of practice, that an important element, the "propelling power," has been omitted.

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