Engineering drawing

“ The work is designed as training for engineers, not draftsmen, therefore an attempt has been made to eliminate copy work as such, and to place stress upon an understanding of what is being done and of the reasons for doing it that way.
The ability to make good freehand sketches rapidly, easily and accurately is an asset to any engineer. Much time and attention is, therefore, devoted to sketching. An engineer must, also, be able to inspect a drawing and know whether or not it is well drawn, accurate and complete, so training is given in checking drawings. ”

“ No amount of care can prevent confusion.
“In the system now proposed the idea of keeping together drawings relating to the same machine, or of classifying them according to subjects in any way, is abandoned, and in place of it is substituted the plan of keeping together all drawings that are made on sheets of the same size, without regard to the subject of them. Nine sizes of sheets were settled upon as sufficient to meet our requirements, and on a sheet that will trim to one of these sizes every drawing must be made. ”

“ If the requirements of a successful draftsman or designer be taken as typical, it is evident that the young engineer must develop, in addition to a technical knowledge of the subject, and a certain degree of skill of hand, a habit of quick and accurate observation and the ability to perceive and retain mental images of forms.
Modern methods of instruction recognize both the motor and mental factors involved in the production of engineering drawings. ”

“ Drawings that are to be intricate, or to contain a great many lines, as a drawing of an engine or of a machine, are best pasted or glued all around the edges of the paper, which should first be dampened; but as the learner will scarcely require to make such drawings until he is somewhat familiar with and well practised in the use of the instruments, this part of the subject need not be treated here. ”

“ Mechanical drawings are seldom tinted, but are mainly produced in India ink. Where, however, a fine effect is desired, working drawings are colored, so as to show at a glance the material of which the different parts are to be made. ”

“ It is by means of this division of the process of manufacture through these drawings, that scores and hundreds of men can be employed at the same time upon a single engine or machine; thus, while handwork has been superseded by machines in many quarters, the art of drawing has not been narrowed nor diminished, for no drawings or designs have yet been made by machinery, nor are they likely to be. ”

“ Stretching or pasting the paper to the board is very seldom resorted to, for the reason that the mechanical drawings are to scale and the paper is natural when pinned to the board and more correct than if under a strain. Mechanical drawings are always required in practice right away, and time would be wasted and lost in damping and pasting and drying again.
A working drawing, whether made to a scale or not, must have all the dimensions plainly written upon it, for a workman should never be compelled to measure a drawing. ”

“ The lines in sectional shading or cross-hatching may be made to denote the material of which the [82] piece is to be composed. Thus Professor Unwin has proposed the system shown in the Figures 95 and 96. This may be of service in some cases, but it would involve very much more labor than it is worth in ordinary machine shop drawings, except in the case of cast iron and wood, these two being shown in the simplest and the usual manner. It is much better to write the name of the material beneath the piece in a detail drawing. ”

“ Whatever the name may be,—Collotype, Artotype, Albertype, Phototype, or Carbon-gravure,—the principle is the same; an impression is made in printer's ink from a photo-chemically produced design on a gelatine surface, either on the hand-press or on a power cylinder press similar to that used in lithographic printing.
There is hardly any process which is more capable of producing fine works of art. It is the only true method for reproducing, in the full sense of the word, an etching, engraving, a drawing in pen and ink, an aquarelle, a painting, or objects from nature. ”

“ It is the numerous inquiries from working machinists for a book of this kind that have led the author to its production, which he hopes and believes will meet the want thus indicated, giving to the learner a sufficiently practical knowledge of mechanical drawing to enable him to proceed further by copying such drawings as he may be able to obtain, or by the aid of some of the more expensive and elaborate books already published on the subject. ”

“ The subscriber, being practically acquainted with all the various kinds of Drawing used, is able to represent Machinery, Inventions, or Designs of any kind, either by Authographic Drawing, or in Isometrical, Parallel, or True Perspective, at any angle best calculated to show the construction of the Machinery of Design patented. ”

“ To prepare a drawing that will be in every way suitable for reproduction usually requires experience of a kind not acquired in many other kinds of drafting, such as preparing engineers' or architects' drawings, because the drawings themselves or blue prints made directly from them are the things the engineer or the architect desires. Drawings prepared for reproduction are generally made larger than publication size, and it is therefore necessary to gage each line, letter, or feature for a definite reduction. ”

“ 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 adaptation to fitting, forging, pattern-making, moulding, and so on. ”

“ In no case is this more surely effected than in the processes of mechanical drawing, where the intended structure has to be portrayed so exactly in plan, elevation, side view, and sections, that the workman has simply to copy the drawing in metal, wood, or stone, as the case may be. It is undoubtedly the fact that mechanicians, engineers, and architects usually possess the faculty of seeing mental images with remarkable clearness and precision. ”

“ This description of drawing is applicable to wood engraving, to line engraving upon copper or steel, as well as to all the methods for automatically producing blocks for relief printing. The line method is also universally adopted by etchers in intaglio.
Successfully to prepare drawings for photographic reproduction it is essential that some knowledge should be possessed of the fundamental principles of {95} photography, as well as an acquaintance with the capabilities of the particular process of production which is to be employed. ”

“ For the most efficient presentation of drawing there will need to be plenty of blueprints or plates from which the student may work. These must be so well executed, as to technique, that the pupil will have before him only the best as models. No one would think of placing before the writing class other than the best models of style and execution in penmanship, yet it is not infrequent to find mechanical drawing students copying from blueprints that are far below standard as to excellence. ”

“ It is now generally recognised that the old-fashioned method of teaching machine drawing is very unsatisfactory. In teaching by this method an undimensioned scale drawing, often of a very elaborate description, is placed before the student, who is required to copy it. Very often the student succeeds in making a good copy of the drawing placed before him without learning very much about the object represented by it, and this state of matters is sometimes not much improved by the presence of the teacher, who is often simply an art master, knowing nothing about machine design. ”

“ As the wood-engraver grew proficient in his technique, he widened his field by imitating the effect of etching or engraving on copper, in rivalry with this form of illustration. In this he succeeded so well that the other, more expensive modes of adornment were largely driven from the field of book illustration. With the advent of photography, the design could be fixed upon the wood block mechanically, accurately, without the trouble of a careful drawing. The values of tone in the photograph relieved the engraver from the work of translating color-values into black and white. ”

“ WE WISH to supplement the preceding pages with a chapter on the technic of wood engraving, and a few words about kindred arts which are of special consequence to the illustrator-printer. The art of wood engraving I consider one of the most valuable things for the illustrator-printer to learn. True, this art is going out of use because of its tediousness; and, it must be confessed, if you wish a picture of a building in your paper, it is much more economical and you can get a better result if you make a pen drawing and send it to be photo-engraved, than if you engrave it on wood. ”

“ It was next found possible, under given conditions, to substitute for the engraver a purely mechanical means, whereby the surface of the block was suitably carved to print with ink the requisite design.
Thus a photographic and chemical process supplants the hand-work of the engraver, and a perfect replica of the original, in no way dependent upon the personal ability of the engraver, is obtained. The same process, working blindly, produces a facsimile equivalent to the artist's own drawing ”

“ They correspond to the sketches made by the engineer or draftsman for drafting-room or shop use. The experience of many instructors seems to indicate that the early introduction of freehand perspective and orthographic sketching in a course of mechanical drawing serves as a means of developing that skill in freehand execution which is so necessary in rendering the freehand features of a mechanical drawing. When this type of skill is acquired before the mechanical work is started, the mechanical and freehand technique may be simultaneously developed. ”

“ Every part laid down should have something to govern it that may be termed a “base”—some position which, if understood, will suggest size, shape and relation to other parts. Searching after a base for each and every part and detail, the draughtsman should proceed upon a regular system, continually maintaining a test of what is done.
A mechanical drawing consists chiefly of three views ”

“ On the other hand, in the old Herbals are cuts of the artist making his drawing from nature, the draughtsman putting it on the block, and the wood-cutter cutting it. When we come to engraving on metal, we find that, though the wood-cutter need not have been an artist, he only having to follow lines given him, or to make certain mechanical ones to suit himself, the metal engraver was obliged to be an artist, because he had to be able to copy the picture or design entrusted to him. ”

“ 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.
A man must have either a natural talent for hand-drawing [138] or years of experience, before he can produce a sketch and “dimension” it, fit to work from ”

“ In one the subject or picture to be reproduced is drawn on the printing stone either with a lithographic crayon or with a pen dipped in lithographic ink or "tusche," which is oily or fatty, like the crayon. In the other method the drawing is made on transfer paper and transferred to the stone. In drawing on stone it is necessary to reverse the design, so that all lettering must be drawn backward. In doing this the artist often uses a mirror to aid him. If the drawing is made on transfer paper the design and the lettering are copied as in the original—not reversed. ”

“ However, in order that acceptable work may be accomplished, fairly good instruments should be procured. The advice of some one experienced in the use and care of draughting tools should be sought before purchasing. A drawing board, a single sheet of paper and a pencil is the simplest “outfit” to be thought of; to this small beginning may be added, soon afterwards, an inexpensive pair of compasses, a T-square and a couple of triangles; a vast range of work can be executed with these few tools. ”

“ In producing this work the author has aimed at placing before young engineers and others, who wish to acquire the skill and knowledge necessary for making the simpler working drawings such as are produced in engineers' drawing offices, a number of good exercises in drawing, sufficient for one session's work, and at the same time a corresponding amount of information on the design of machine details generally. ”

“ After allowing the composition to cool partly, yet while soft enough to stick, the piece of work that is to be embossed is placed on it, the right side next to the pitch. It is then allowed to cool still more; when quite hard or when it is difficult to make an impression on it with the thumb nail, it is ready to work on. The design is next drawn or transferred to the metal by the use of carbon paper and then scratched on with a scratch awl to make the drawing more permanent, as in going over the piece of work the pencil or carbon lines are easily erased. ”

“ Ordinarily we do not recommend to the printer to experiment with such effects, but rather to confine himself to outline or silhouette, but the value of the white-line will be considered in connection with wood engraving, and any practice in drawing from nature in light masses will help you appreciate the judicious use of white-line in wood engraving, or strong contrasts of white and black in any medium. ”