[iii]
The object of this book is to enable the beginner to learn tomake simple mechanical drawings without the aid of an instructor,and to create an interest in the subject by giving examplessuch as the machinist meets with in his every-day workshop practice.The plan of representing in many examples the pencil lines, andnumbering the order in which they are marked, the author believesto possess great advantages for the learner, since it is the producingof the pencil lines that really proves the study, the inking in beingmerely a curtailed repetition of the pencilling. Similarly whenthe drawing of a piece, such, for example, as a fully developedscrew thread, is shown fully developed from end to end, even thoughthe pencil lines were all shown, yet the process of construction willbe less clear than if the process of development be shown graduallyalong the drawing. Thus beginning at an end of the example thefirst pencil lines only may be shown, and as the pencilling progressesto the right-hand, the development may progress so thatat the other or left-hand end, the finished inked in and shadedthread may be shown, and between these two ends will be found apart showing each stage of development of the thread, all the linesbeing numbered in the order in which they were marked. Thisprevents a confusion of lines, and makes it more easy to follow orto copy the drawing.
[iv]It is the numerous inquiries from working machinists for a book ofthis kind that have led the author to its production, which he hopesand believes will meet the want thus indicated, giving to the learnera sufficiently practical knowledge of mechanical drawing to enablehim to proceed further by copying such drawings as he may beable to obtain, or by the aid of some of the more expensive andelaborate books already published on the subject.
He believes that in learning mechanical drawing without the aidof an instructor the chief difficulty is overcome when the learnerhas become sufficiently familiar with the instruments to be enabledto use them without hesitation or difficulty, and it is to attain thisend that the chapter on plotting mechanical motions and the succeedingexamples have been introduced; these forming studies thatare easily followed by the beginner; while sufficiently interesting toafford to the student pleasure as well as profit.
New York, February, 1883.
[v]
PREFACE. |