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 the drawings 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 any time understood and adopted except by those who have cultivated a taste for order and regularity.