XXVI The Teaching of Mechanical Drawing
Mechanical drawing a mode of expression
Drawing is a mode of expression and is therefore a form of language. As applied in the engineering field drawing is mechanical in character and is used principally 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.
Mechanical drawing disciplinary as well as practical in value
Engineering drawing demands intellectual power quite as much as it does skill of hand. The draftsman in conceiving 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 standards of technique and methods of representation found in the best commercial practice; likewise to develop in him the powers to visualize and reason, which are possessed by the commercial draftsman and designers.
Organization and content of courses in mechanical drawing
The drawing courses of engineering curricula may be divided into two groups: (1) General courses, in which the principles and methods of representation are taught, together with such practice in drawing as will develop a satisfactory technique. (2) Technical courses, the aim of which is to assist the student to acquire technical knowledge or training, drawing being used primarily for the purpose of developing or testing a student’s knowledge of the subject 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
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 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.
Fundamentals of the elementary course
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 invoke the making of arrowheads, letters, and numerals. In such an elementary course the student receives not only the training in the fundamentals, but also in their application in working drawings which furnish complete and accurate information in the desired form.
Descriptive geometry
The modern methods of teaching descriptive geometry apply the theory of the subject to applications in problems taken from engineering practice. The introduction of practical applications adds interest to the subject and makes the theory more easily understood. The number of applications should be as great as possible without interfering with the development of the theory. Such a treatment of descriptive geometry, following a thorough course in elementary drawing, should make it possible to deal with abstract principles of projection with a few well-chosen applications.
Descriptive geometry aids materially in developing the power of visualization which is so essential to the training of the engineer. The graphical applications of the subject in the solution of engineering problems may be used as a means of testing the student’s ability to visualize.
There is now very little discussion relative to the advantages and disadvantages of the first and third angle projection. Since the third angle is generally used in the elementary course as well as in engineering practice, it seems logical that it should be emphasized in descriptive geometry. Recent textbooks on this subject confirm the tendency toward the use of the third angle.
The use of the third angle presents new difficulties, such as that of locating the positions of magnitudes in space in relation to their projections. Magnitudes must be located behind or below the drawing surface. To obviate such difficulties, some instructors demonstrate principles by first angle constructions. Others invert surfaces which in the first angle have their bases in the horizontal plane. This undesirable device may be overcome by using a second horizontal plane in the third angle. Such means of demonstration may be avoided altogether by considering the space relations of magnitude to one another instead of relating them to the planes of projection. This method centers the attention of the student on the relation of magnitudes represented and develops visualization. It has been found to give excellent results in both elementary drawing and descriptive geometry.
To bring the teaching of descriptive geometry into closer harmony with its application in practice, auxiliary views are frequently used instead of the method of rotations.
Briefly, then, it appears that the modern course in descriptive geometry should contain enough applications to hold the interest of the student and to test his power of visualization; that the third angle should be emphasized, and some use should be made of auxiliary views. Above all, the development of visualizing ability should be considered one of the chief aims of the course.
Methods of instruction in general courses
In teaching drawing and descriptive geometry, lectures, demonstrations, and individual instruction each have a place. Principles can best be presented in the form of lectures. The manual part of the work can be presented most effectively by means of demonstrations. The instructor should illustrate the proper use of instruments and materials by actually going through the process himself, calling attention to important points and explaining each step as he proceeds. Individual instruction given at the student’s desk is a vital factor in teaching drawing, as it offers the best means of clearing up erroneous impressions and ministering to the needs of the individual student.
Frequent recitations and quizzes serve the purpose of keeping the instructor informed as to the effectiveness of his instruction and as a means by which the student can measure his own progress and grasp upon the subject.
Methods of instruction in technical drawing courses
Those drawing courses which have for their primary object the teaching of technical subject matter make use of the drawings as an instrument to record facts and to test the student’s knowledge of principles and methods.
In the technical courses it should be possible to assume a knowledge of the material given in the general courses. Some effort is usually necessary, however, to maintain the standards already established. The effort thus expended should result in improving technique and increased speed.
The four-year drawing course
In an institution where drawing courses are given throughout the four years, much can be done by organization and coöperation to make the time spent by the student productive of the best results. More time than can usually be secured for the general courses is necessary to develop skill that will be comparable with that found in practice. The conditions in technical drawing courses approximate those in practice. They apply methods taught in the general courses. The limited time, frequently less than 300 clock hours, devoted to the general courses makes it desirable that advantage be taken in the technical courses for further development of technique and skill. In a number of institutions all work in drawing is so organized as to form a single drawing unit. This plan calls for coöperation on the part of all drawing teachers in the institution. The results obtained by this method seem amply to justify the effort put forth.
Conclusion
The final test in any course or group of drawing courses may be measured by the student’s ability to solve problems met with in engineering practice. Measured upon this basis, the newer types of courses discussed herein, those founded upon the analytic method and developed largely as a progressive series of working drawings, seem to be meeting with better results than did those of the older type in which the synthetic method predominated and in which abstract problems were principally used.
While the college man is not fitting himself to become a draftsman, it is quite true that many start their engineering careers in the drafting office. Those who think well and are proficient in expressing their thoughts through the medium of drawing are most apt to attract attention which places them in line for higher positions.
Those who do not enter the engineering field through the drafting office will find the cultural and disciplinary training and the habits of precision and neatness instilled by a good course in drawing of great value.
J. D. Phillips and H. D. Orth
University of Wisconsin