N. Hawkins

“ We see by the agency of light, as all objects, except such as may be styled self-luminous, when placed in a dark chamber are not perceivable by us, except by touch, smell or hearing; we cannot see them; they are invisible. But when, by removing a shutter or igniting a flame, we introduce something to the chamber which was not present when the chamber was dark, we become at once conscious of the appearance of the object, we perceive it by the sense of sight. ”

“ Real, or true perspective, represents the object exactly as it is seen in nature, where the parts that are far away from the eye of the observer appear smaller than those nearby. Occasions arise, however, in practical life, with its numerous phases of industrial requirements, where the convenience of showing the complete form of the object in a single view might preferably be coupled with the convenience of scale dimensions. ”

“ A single word of advice before introducing the elementary work connected with mechanical drawing: if the student should experience difficulty in mastering the diagrams and curves abounding in this book, let him consult an experienced draughtsman or teacher, who, by a few strokes of a lead pencil, can easily make them plain; that knowledge—which cannot be printed or self-taught—termed the Craftsman’s Art, is communicated largely by personal telling and showing, from man to man; in drawing, this help should be thankfully availed of, when necessity arises. ”

“ All this time that you have been studying mechanism you should have had a sketch book or pad of note paper, and made free hand sketches of mechanical movements which interested you and of various machine details. You should accustom yourself to use drawing as a means of expressing ideas, just as you use written words, so that it becomes a second nature to you to sketch anything you wish to remember or describe. If you work from blue-prints in the shop, or if you can borrow some to study, this will help you to understand how a drawing is made. ”

“ The application of the science of geometry to the drawing-board is absolutely necessary to success, for the reason that the whole fabric of mechanical drawing rests on the principles of geometry, which is well termed the science of measurements. ”

“ It is a question how far a good working knowledge of drawing can be attained without a teacher; it is true that but few have become proficient without such aid, but it is equally true that “self-help” has been the key note to all advancement. ”

“ It may be remarked that they only draw well who draw intelligently; aptness in this, as in many other virtues, is a matter of slow growth, “here a line and there a line”—it’s the proper direction, not the rate of progress, that counts in the end.
There are several methods of drawing—1, Free-hand; 2, Instrumental; 3, Geometrical; 4. Perspective. In the first the work, also termed sketching, is executed by pencil, pen, crayon, or even paint-brush; in the second the result is attained by the use of rule, tee-square, drawing pen, etc. ”

“ A mechanical drawing is the vehicle for conveying the ideas of the designer to those who are to embody them in wood and metal, and the considerations which should govern its production are those which affect its clearness and legibility or those which facilitate reference to it.
Drawings consist of 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 vertical planes; and sections, views taken on bisecting planes, at any angle through an object. ”

“ SOLID.—A solid has three dimensions—length, breadth and thickness.
SPHERE.—A solid bounded by a curved surface every point of which is equally distant from a point within called the center.
SURFACE.—The boundary of a solid. It has but two dimensions—length and breadth. Surfaces are plane or curved.
A Plane Surface is one upon which a straight line can be drawn in any direction.
A Curved Surface is one no part of which is plane.
The surface of the sphere is curved in every direction, while the curved surfaces of the cylinder and cone are straight in one direction. ”

“ The only reminder of the top view is the eye or point of vision, the picture plane that falls together for the sake of convenience with the horizon of the end view and the ray that determines the measurement point M, which is, in this suppressed reproduction, absolutely necessary, in order to find the apparent position of the real corners behind the picture plane. ”

“ The approximate or scale perspective completely avoids all the difficulties of choosing a point of sight, of having several views, vanishing points and measurement points, and thus offers a representative view, with a great saving of time and labor. Particularly for mechanical purposes, where an artistic impression is not called for, it presents a distinct advantage over the true or real perspective. ”

“ THE PERSPECTIVE PLANE is an upright square of glass, usually framed like a picture, with a base, so that it can stand up alone. This is placed between the eye of the spectator and the subject to be drawn, and as the drawing is sometimes made directly upon it, it is sometimes called the Picture or the Plane of the Picture.
Fig. 301.
HORIZONTAL means perfectly level, like the surface of still water. We must be careful to understand perfectly the difference between the terms “level” and “even” or “flat.” A surface may be even or flat, without being level. ”

“ A point is mere position, and has no magnitude.
A line is that which has extension in length only. The extremities of lines are points.
A surface is that which has extension in length and breadth only.
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A solid is that which has extension in length, breadth and thickness. ”

“ To be introduced for the first time into such a company is a trial for the “new man” both of nerve and manners, and a test as well of skill; nothing helps more at such a time than an acquaintance with the rules and routine of the office, for the old saying holds good in a drawing office, of “doing in Rome as the Romans do.” ”

“ If all the fine sets of drawing instruments that are owned by workmen were put to frequent use the owners would find a marked improvement in their abilities in other lines as well as drawing; for it is a noticeable fact that when a person’s mind has been trained in a business that requires close calculation and a knowledge of materials, he is capable of showing good qualifications in other lines, and the more skilled he is in one the easier can he acquire skillfulness in another, if he applies the same amount of energy, thought and interest as he did to acquire skill in the first. ”

“ When you have become sufficiently familiar with the principles of drawing, a book on mechanism will tell you how to draw gear teeth and cams, and how to design various link motions. Make up your own problems from what you see in the shop and make your drawing a means to an end and not the principal thing; it is of little use to be able to make a nice drawing unless you know what to draw and why. ”

“ Either system can have, however, the plane II at the right- or left-hand side edge, while plane III may be attached to the top or bottom edge of plane I; it is readily understood that a number of combinations are possible for each system, as it is not necessary to adhere absolutely to one rule. The system of forward projection is the one generally practiced and further examples are all executed by this system, meaning that the planes are always between the observer and the object. ”

“ 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 figuring and lettering should be always done with India ink, thoroughly black; the last lines to be drawn are the section lines. The reason why irregular curves and arcs of circles are inked in first is, that it is easier to draw a straight line up to a curve than to take a curve up to a straight line.
In practice, the flat side of the drawing-pen is laid against the tee-square or ruler; the taper of the blade of the pen is sufficient to throw the point enough away from the edge to prevent blotting; the pen is drawn from left to right and from the bottom to the top of the board. ”

“ To represent an object in perspective, the horizon and the point of vision will have to appear in the drawing as the fundamental starting points.
Three dimensions are distinguished for the fixing of an object in space from a certain reference point. They are height, breadth and thickness, and are in their direction square to each other. The height is the fundamental direction, being derived from the direction of gravity, that invariably extends to the center of the earth. ”

“ Fig. 55.
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Free-Hand Drawing.
A free-hand drawing is executed with the unaided hand and eye, without guiding instruments or other artificial help. It is necessary to be known that all drawing required cannot possibly be done by rule and compass, but that some portions must be drawn “free-hand,” trusting to the eye alone.
Hence, it is important that the student should be able to sketch at sight from objects he may see, or to draw roughly, with a piece of chalk or a pencil, pieces of mechanism required to be represented. ”

“ It is not expected that all should exhibit a decided taste for drawing, for the possession of this is rather a gift of nature than the result of education; but a knowledge of principles and a certain amount of executive ability [22] may be obtained by every one of average capacity, and whatever the natural power may be, it will be increased and developed by exercise; if the progress is steady and continuous and in the right direction, success is sure to crown the work. ”

“ When the invention consists of an improvement on an old machine, the drawing must exhibit, in one or more views, the invention proper, disconnected from the old structure, and also, in another view, so much only of the old structure as will clearly show the connection of the invention with the old machine. ”

“ Practice in chalk-work should alternate with sketching in a sketchbook and with geometrical drawing—to be hereafter described. The student should practice a short time on the board, at least once a week; large sizes are the most profitable for the representations to be made; when drawing in different directions the hand should be turned, not the paper or board; the hand should never be allowed to obstruct the sight, hence the hand and fingers should be held in a position of freedom—with fingers not nearer than 11⁄2 or 2 inches from the board. ”

“ A tracing is a mechanical copy of a design or drawing, made by reproducing its lines as seen through a transparent medium—as tracing-cloth or tracing-paper.
Tracing-cloth is a thin linen fabric, coated with size; this is called tracing-lines; tracing-paper is so prepared as to be transparent, so that it will receive marks either in pencil or with pen and ink.
Tracing-cloth must be fastened to the board, over the drawing, by pins or other tacks; moisture or dampness should be carefully avoided and the drawing done on the smooth side of the cloth. ”

“ When the teeth of bevel gears form an angle of 45° they are called miter wheels.
Miter wheels to gear must be of equal sizes.
A crown wheel is a disc that has teeth which are on its side face; that is, teeth on a flat circular surface all parallel to the axis of the wheel.
A rack has teeth on a flat surface or plane all parallel to one another.
A gear cut by machine is called a cut gear. It has teeth with less clearance than cast wheels, which are not so true or perfect, and therefore require more clearance. ”

“ From the pitch all the proportions and measurements for the sizes and strength of the parts of the wheel are taken by rule, and a symmetrical form is produced.
In machine drawing the practice is to represent wheels by circles only; the teeth are never shown except on enlarged details and then only in very rare instances; the circles drawn are always the pitch lines or the rolling points of contact of the wheels.
The addendum circle is seldom if ever used in practical drawing. Should it be necessary to show it in an exceptional case, the circle would be represented by “dotted” line. ”

“ In working to regular scales, such as 1⁄2, 1⁄8, or 1⁄16 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.
The protractor shown in fig. 193 is an instrument for laying down and measuring angles on paper; it is [129] used in connecting with a scale to define the inclination of one line to another. ”

“ The word perspective means to see through; the word perspective being derived from the Latin word perspicere, to look through, hence, perspective is a science which teaches us to see correctly and enables us to represent the appearance of anything we may wish to draw; care should be taken in perspective drawing, to select objects interesting in themselves, and the best specimens of their class, so as to cultivate taste, while they at the same time afford useful and instructive drawing lessons. ”