XXVI THE TEACHING OF MECHANICAL DRAWING D Mechanical drawing a RAWING is a mode of expression and is therefore a form of language. As applied in the engineering field mode of drawing is mechanical in character and is used principally expression for the purpose of conveying information relative to the construction of machines and structures. It seems logical that the methods employed and the standards adopted in the teaching of engineering drawing should be based on an analysis of conditions found in the engineering world. In the best engineering practice the technical standards of drawing are high, so high in fact that they may be used as an ideal toward which to work in the classroom. Examples of good draftsmanship selected from practice may well serve to furnish standards for classroom work, both in technique and methods of representation. disciplinary as well as in value practical Engineering drawing demands intellectual power quite Mechanical as much as it does skill of hand. The draftsman in con- drawing ceiving and planning his design visualizes his problem, makes calculations for it, and graphically represents the results upon the drafting board. The development of the details of his design makes it necessary that he be a trained observer of forms. Since new designs frequently involve modifications of old forms, in his efforts to recall old forms and create new ones, he develops visual memory. 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. It is the aim of the drawing courses in engineering colleges to familiarize the student with the Organization and content of courses in mechanical drawing standards of technique and methods of representation found The drawing courses of engineering curricula may be matter. The general courses usually include an elementary course and a course in descriptive geometry. These courses deal with the fundamental principles and methods which have universal application in the advanced and technical courses. While the courses of the two groups may overlap, the general courses precede the courses of the technical group. There is no general agreement as to the order in which the subjects belonging to the general group should be given. Each of the following orders is in use: 1. A course in descriptive geometry followed by an elementary technical course. 2. An elementary course and a course in descriptive geometry given simultaneously. 3. An elementary course followed by a course in descriptive geometry. The first plan is followed by a number of institutions which conclude, because of the general practice of offering courses in drawing in the secondary schools, that pupils entering college have a knowledge of the fundamentals ordinarily included in an elementary course. In other institutions it is held that the principles of projection can be taught to students of college age in a course of descriptive geometry without preliminary drill. Where the second plan is used, the courses are so correlated that the instruction in the use of instruments given in an elementary course is applied in solving problems in descriptive geometry, while the principles of projection taught in descriptive geometry are applied in the making of working drawings. This plan is followed by several of the larger engineering colleges. Under the third plan the principles of projection are taught through their applications in the form of working drawings. In this way the principles may be taught in more elementary form than is possible in any adequate treatment of descriptive geometry. The illustration of the principles in a concrete way makes it possible for those who find visualizing difficult, to develop that power before abstract principles of projection are taken up in the descriptive geometry. The skill of hand developed in the elementary course makes it possible to give entire attention to a study of the principles in the course in descriptive geometry. While excellent results are being obtained under each of the three plans, this plan is the one most generally adopted. The order of courses in the technical drawing groups is determined by other considerations than those relating to drawing, such as prerequisites in mathematics, strength of materials, etc. The elementary courses have undergone a number of important changes during recent years. In those of the present day more attention than formerly is given to the making of complete working drawings. In the earlier courses the elements were taught in the form of exercises. In the latter part of the courses the elements were combined in working drawings. In the modern courses, however, there is a very marked tendency to eliminate the exercise and make the applications of elements in the form of working drawings throughout the course. In the early type of course the theory of projection was taught by using the synthetic method; i. e., by placing the emphasis first upon the projection of points, then lines, surfaces, and finally geometrical solids. In the modern type of course, however, this order is reversed and the The ele mentary courses Fundamentals of the elementary course analytic method is used; i. e., solids in the form of simple machine or structural parts are first represented, then the principles of projection involved in the representation of their surfaces, edges, and finally their corners are studied. In this type of course the student works from the concrete to the abstract rather than from the abstract to the concrete. Geometrical constructions, which were formerly given as exercises and which served as a means of giving excellent practice in the use of instruments, are now incorporated in working drawings and emphasized in making views of objects. It is believed that in the applied form these constructions offer the same opportunity for the training in accuracy in the use of instruments that was had in the abstract exercises, to which is added interest naturally secured by making applications of elements in working drawings. Conventions are also taught in an applied form and are introduced as the skill for executing them and the theory involved in their construction are developed in the progress of the course. The type of freehand lettering most generally taught is that used in practice; i.e., the single-stroke Gothic. The best commercial drafting-room practice suggests the use of the vertical capitals for titles and subtitles, and the inclined, lower case letters and numerals for notes and dimensions. The plan generally found to produce satisfactory results is to divide the letters and numerals of the alphabet into groups containing four or five letters and numerals on the basis of form and to concentrate the attention of the student on these, one group at a time. The simple forms are considered first, and enough practice is given to enable the student to proportion the letters and numerals and make the strokes in the proper order. It is more natural to make inclined letters than vertical ones, and they are therefore easier to execute. If both vertical and inclined letters are taught, the instruction on the vertical should be given first, as it is more difficult to make vertical strokes after becoming accustomed to the inclined strokes. Freehand perspective sketching affords the most natural method of representing objects in outline. It is of particular value in interpreting orthographic drawing. The student who first draws a perspective sketch of an object becomes so familiar with every detail of it that he cannot fail to have a clearer mental image of its form when he attempts to draw its orthographic views. It gives a valuable training in coördinating the hand and eye in drawing freehand lines and estimating proportions. It also serves as an intermediate step between observing an object and drawing it orthographically. Freehand orthographic sketching is now quite commonly incorporated in modern courses in mechanical drawing. Such sketches serve as a preliminary step in the preparation of the mechanical 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. The organization of an elementary course composed largely of a progressive series of working drawings necessitates the giving of considerable attention to the selection of problems involving the use of the above-named fundamentals to make the course increasingly difficult for the student. The drawing of views involves geometrical constructions and conventions, while the dimensions, notes, and title involve the making of arrowheads, letters, and numerals. In such an elementary course the student receives not only the training in the fundamentals, but also |