Although there are many excellent works on the market covering in a more or less complete way the subject of Mechanical Drawing and Practical Drafting, it has been my experience that most of these are not sufficiently extensive and practical to admit their use in schools where it is necessary to devote a large amount of time to the subject, or in classes composed of men wishing instruction of a practical nature. The course as herein presented has proven its worth, and large numbers graduated from it have experienced no difficulty in securing and retaining drafting positions. Sufficient ground is covered in the elements of Mechanical Drawing to insure a solid foundation for the work of a more practical nature following. I hope that this book will prove to be all that I think it to be. I am exceedingly anxious to make any desirable improvements, and would therefore welcome suggestions from either the teacher or the man in the office. Several important changes have been made in this edition. Material has been added which should improve the course presented, and every effort has been made to make the work as it should be. It is hoped that these changes and additions will prove valuable to both the teacher and student and add greatly to the efficiency of the book as a means of properly imparting a knowledge of the subject which it represents. This text is especially intended for use in the class room. Every effort has been made to produce an ideal text for this purpose.


THINGS A GOOD DRAFTSMAN SHOULD REMEMBER. (READ CAREFULLY.)

Be neat and accurate, and keep busy. Study the problem before attempting its solution. Don't be afraid to ask intelligent questions. Keep the pencil sharp and the instruments clean. Always clean a pen before using. Use the T square by placing the head on the left hand side of the board. Use the triangles against the T square. Become familiar with the use of the scale as soon as possible. Practice lettering continually. It is well to learn to make both the slant and vertical types, but it is better to be good at one than just fair at either. The general appearance of a drawing depends largely upon the lettering. Always make a pencil drawing complete, even though it is to be inked or traced. When inking or tracing a drawing, draw the lines in the following order: Center lines (very light, dot and dash); all arcs and curves; full straight lines; dotted straight lines; cross section lines (45 degrees when possible); arrowheads; dimensions; lettering; border line and title. Make dotted and center lines lighter than the others. The drawing should always be checked before being inked or traced. The title should include the name of the object drawn, the scale used, by whom drawn, the date finished, and the number of the drawing. Learn to make sketches from actual machine parts, and remember that a sketch isn't worth much unless it is properly dimensioned. Before starting to trace a drawing it is well to rub the cloth well with “ponce” or powdered chalk. When erasing use a pencil eraser, especially if the surface is to be inked over again. Erase lightly. Make shade lines by drawing several lighter ones. Dimensions under two feet are usually expressed in inches; those over two feet in feet and inches. Make the sheet balance. Draw to as large a scale as possible.


DETAIL AND ASSEMBLY DRAWING

The more practical work of the course begins with Plate 41. All work must be laid out in pencil first, and the pencil drawing must be just as complete as the finished drawing is to be. Neat work is exceedingly important. The appearance of the plate will depend much upon the way the lettering is done. Many sketches are given, but this does not imply that students are to make a sketch. Follow dimensions and make a finished drawing. Ink or trace according to directions. Students should study the several plates very carefully before proceeding with the work.

Pages 60 and 61 contain sketches of the objects drawn on the plates designated. These sketches should be carefully studied before and while drawing the object in orthographic projection.

Several plates require that a sketch be made of an object, the object measured, and the dimensions obtained to be put upon the sketch. This should be very carefully done, a particular effort being made to get all of the necessary dimensions on the sketch.

All assembly drawings must represent the very best skill of the student; Great care should be taken with the drawing of the different kinds of lines. No assembly drawing is to contain free-hand lettering. All letters must be drawn with the instruments.

When a drawing is to be traced stretch the tracing cloth over the drawing and ink in the same way as when a pencil drawing is inked. The dull side of the cloth is generally used.


PERSPECTIVE DRAWING

If one were to look out of the window at a building, and if a line could be drawn from every point of the building to the eye of the observer, the points on the window where the lines pierced it would be the ones to be connected if a picture of the building was to be drawn upon the window. The window corresponds to the picture plane in perspective drawing the plane upon which the observer and object rest is the horizontal plane called the ground the plane parallel to the ground and passing through the eye of the observer is the plane of horizon.

Study Plate 72 very carefully and note the following: A B is a top view of the picture plane C D is a front view of the plane of horizon E F is a front view of the ground plane. The station point (the point at which the observer stands) is usually taken at about one and one half the height of the object in front of the picture plane. This point must be selected to show the object to the best advantage. The line of horizon is generally taken from five to six feet above the ground. Note that the vanishing points are obtained by drawing lines from the station point parallel to the faces in the top view until they intersect the picture plane, and then dropping perpendiculars to the line of horizon. Note how lines are drawn from each point of the object in the top view to the station point and perpendiculars, then dropped from the intersections of these lines with the picture plane.

Obviously, in reality, the object would never be against the picture plane. Plates 72 and 73 show it in this position, but this is done so that the student will master the principles of perspective easier. The remaining plates are to be drawn with the object away from the picture plane.

All of the perspective drawings are to be inked and shaded. If all dotted and construction lines are drawn in red ink the general appearance of the drawing will be greatly improved.