This book is written for the purpose of assisting the student to knowledge of the principles of mechanical drawing and their practical applications. It is not intended to be a manual of self-instruction, but rather an assistant to the teacher in reinforcing his presentation of the subject matter and in supplying him with convention, data, and problem sheets, the preparation of which ordinarily consumes much of his time and energy.

It is believed that the treatment of the subject, as presented here, will be found to stimulate the interest of the student and to serve a much more useful purpose than does the formal drawing usually taught.

A course of study will not be found in this book. A definite course planned to cover all schools would be adapted to none, because conditions vary locally and are changing from year to year; but any teacher may select and arrange a course, closely adapted to his needs, from the supplementary loose-leaf sheets which are published with the Drafting Series. These sheets contain informational instruction, such as conventions and data, and also problems. A list of these sheets may be procured from the publishers of this book. Additions to the list will be made from time to time, and teachers are requested to correspond with the author and to express their views and wishes.

The plan of supplying a text, the principles of which do not change greatly from year to year, in combination with loose-leaf sheets, which can be selected and arranged to suit individual requirements, will enable a large number of teachers to formulate a course of study adapted to the needs of their classes.

Drawing instruments and materials generally are furnished by the schools and therefore all information relating to their selection is omitted.

The author believes that the chief value of knowledge of mechanical drawing is its utility as a medium of expression, and this text has been prepared from this point of view. There can be no question, also, as to its helpfulness in the study of applied geometry, but the amount of time that may usually be devoted to mechanical drawing is so limited the author feels that it should be spent entirely in acquiring a knowledge of and skill in drafting rather than in the solution of numerous geometrical problems, which are seldom used in practice, and most of which can be solved by the use of T square and triangle instead of by geometrical methods.

On the other hand, the study of orthographic projection is essential to a thorough course in mechanical drawing. Projection should be presented through the solid, avoiding as much as possible the difficult terms and methods of descriptive geometry. The third angle, only, should be studied for the following reasons: First, it is used almost exclusively in drafting offices; second, the principles of projection are the same for all angles; third, a better understanding of the subject will be secured by concentrated drill upon the principles as applied to one angle only.

The sequence of the subject as here presented is more a matter of convenience than an arrangement for a course of study. The author has made it a practice to begin with very simple working drawings and to introduce isometric drawing, after a few lessons, translating freely from one form of expression to the other. This method will greatly assist the pupil in learning to read drawings, I. e., to visualize the object. In this stage, the actual object should be employed as the basis of the freehand sketch, which may be rendered either in views or isometric. Considerable emphasis should be placed upon this phase of the instruction and several lessons should be given in the above manner, preceding the use of instruments.

Following this there should be considerable practice in the application of principles in the making of isometric and working drawings with instruments, both in detail and assembly. Simple projections, without dimensions and omitting all reference to the theory, may be presented next.

Simple problems in machine and plan drawing, working from sketches, models and blue-prints are next in order. Isometric and perspective sketches should be used freely in presenting the material for working drawings. Mere copying from blue-prints should be avoided except for purposes of conventional rendering. In drawing plans the pupil should begin with the representation of a very simple floor plan and elevation drawn to a scale of f in. = 1 ft. The representation of doors and windows in elevation should then be studied and applied to a simple problem. This should be followed by studies of structural details in section and isometric drawing. Next, he should copy the plans and elevations from a good design of a small house, making only slight modifications as directed by the instructor. After obtaining some proficiency in problems of this character he may essay to work a problem from his own sketches.

After the pupil has studied geometry as a mathematical subject, the principles of orthographic projection should be taught, followed by intersections and developments. He will then be ready to undertake advanced drafting courses along some special line leading eventually to skill and thoroughness in that branch.

The teacher should always insist that drawings be “blocked in” by fine, light, solid lines which are to be left on the finished drawing but not inked. This will facilitate the checking of drawings and will also serve as an indication that the pupil is following practical methods in drafting.

CHARLES B. HOWE.