This treatise is intended to teach the practical application of the principles of projection to the illustration of machinery; to inform the student concerning many of the exceptions to the laws of projection; and finally, to furnish such practical examples as may serve for problems to the student, and suggestions to the draftsman. It aims to encourage a concise graphic expression in the colloquial phrases of modern mechanical drawing, instead of the more classic language which would enforce a rigid adherence to the laws of projection, and the customs of several centuries of architectural draftsmen.

The examples chosen are those which, being faithfully and intelligibly executed, will enable the student to acquire much practical information on the subject by the making of only a few drawings. The number of subjects suitable for these exercises is surprisingly small; for at this period of the student's advancement, it is the art of graphic expression rather than that of drawing which is most required, and this cannot be attained by the making of copies. It is, indeed, almost a waste of time to copy a drawing; since proficiency in penciling may be better acquired by other means, and tracing is much superior as an exercise in inking. The difficulty in obtaining suitable models has, however, necessitated much of this; but it is hoped that the present volume may assist in obviating the trouble by supplying such problems as may lead
the student to observe closely, think accurately, and express clearly. The subjects chosen for the exercises are such as have been found suitable for illustrating most of the principles taught, as well as the practical suggestions made in this book.

Much care has been exercised in the making and figuring of these drawings, that they should be complete and correct; but that this should be realized in every detail, is more than the author s experience would lead him to expect. While it is to be desired that the one great lesson of accuracy should be emphasized above all others, it is also to be remembered that draftsmen are not infallible, and it is the minimum, rather than the absence, of mistakes by which we are to judge.

As this book is the advocate of no special systems of lining, figuring, lettering, etc., the plates will be found to represent a variety of types in drawing which may at some time serve the draftsman who is not bound to special methods, but seeks the one and only end to lye attained; namely, the art of using all available instrumentalities in securing a terse, accurate, and complete expression of mechanical ideas.

GARDNER C. ANTHONY.

 
Technical Drawing is a graphic language, and may best be studied by subjecting its use to laws similar to those governing other languages. Like others, it has its orthography, grammar, and literature. Its orthography, consisting of the various t5rpes of lines; its grammar, being the art of representing objects upon planes, and known as orthographic projection; and finally its literature, consisting of the practical application of these principles to the drawings which we are required to read and write. But in this, as in all languages, we cannot be governed entirely by laws, but must familiarize our-selves with the idioms and (conventional methods of the day, remembering always that it is simply a medium for the expression of our thoughts.
 
A drawing fulfills its object only when it clearly sets forth the ideas to be expressed, and in nowise misleads the reader to whom it is especially addressed. If it fails to do this, it is a poor drawing, regardless of the fact that it may conform to all established laws, and be executed with the greatest precision and elegance. A drawing should be regarded as a business letter to the mechanic, and must first of all be brief, having as few lines and figures as possible. It must completely express the idea, omitting no lines or views necessary to attain this end. It must contain nothing that may mislead, even though it be to violate the laws of projection. The character of the di-awing must be determined by the use to which it is put. If a free-hand sketch is sufficiently comprehensive, and will in every way serve the purpose of the finished drawing, it is a waste of labor to make the latter. On the other hand, no pains should be spared in the execution of the drawing if it will better express the designer's conception of the mechanism. No portion of such work should be carelessly done, even in the so-called off-hand sketch, or drawing. A sketch may consist of few lines and be comparatively rude, but it must not be thoughtlessly executed. Again, the draftsman must consider the class of mechanics to whom his drawing is addressed. He should anticipate their wants, and, to a certain extent, guard against mistakes which may arise from their ignorance. Experience alone will make a man proficient in the use of this graphic language, but a knowledge of the laws governing it will greatly facilitate its acquisition.
 
The development of machine drawing, during the last few years, has resulted in the introduction of many methods and technicalities which were not formerly required. The technical part of architectural drawing has never necessitated such rigid conformity to laws concerning the arrangement of views, methods of sectioning, figuring, and other details; and it is for this reason that many apparent innovations have necessarily been made upon the old established systems of drawing. No one change has caused more discussion than the rigid adherence to the representation of all objects in what is known as the third angle of projection, that is, the placing of the top view on the top of the sheet, the view of the right-hand on the right-hand of the sheet, etc.; in short, placing the view nearest to the face which it represents. But this has now passed the stage when the advantages to be derived by this method may be questioned, and to-day no well conducted drafting room will permit any other system to be used.
 
This treatise presupposes a knowledge of the use of instruments and the theory of orthographic projection. Its aim is to teach the more concise methods of graphically expressing mechanical ideas.
 
12. Classes of Drawings. The different types of drawing required for shop uses are as follows:
 
The General or Assembled Drawing. This consists of a representation of the complete machine, with all of its parts sustaining their proper relations to each other. This drawing may contain information suitable only for assembling the machine, and illustrating the general design; or it may also include some or all of the details of the machine. The drawing of the Tail Stock, Plate 12, is of this type.
 
Detail Drawings. These illustrate each piece separately, with all of the information necessary for its construction. This type is shown by Plates T and 8. It is customary to devote one or more sheets to forgings, and others to castings, or when the parts are few in number they may be placed on a single sheet.
 
Bolt Drawings. Where a great variety of bolts is used on a machine, a special drawing of them is required, or a Bolt List may be prepared which shall enumerate the sizes, type, and number of each.
 
Motion Diagram. This type would be used only in complicated machinery comprising a number of mechanical motions more or less complicated. Such a drawing would instruct concerning the relation of important centers, direction of motion, relative velocity of shaft, etc.
 
13. The Lay-out of the Drawing. The size of paper used for the drawing is usually determined by certain fixed standards peculiar to each shop and largely dependent on the uses for which the drawings are designed. For the problems of this book, the sizes of 10 x 14 and 14 x 20 inches are recommended; but nearly all of the work may be drawn on the smaller size. These dimensions are for the margin line, the size of the paper being as much greater as may seem suitable. From one-half to one inch margin is sufficient. Having put down the paper and ruled the margin, obtain a "lay-out" of the pieces to be represented. This consists in the making of a rude sketch of the various parts and views to be put on the drawing, so that ample room shall be provided for each piece, and the whole be symmetrically arranged. This operation is usually neglected by students, and inevitably leads to trouble, and the loss of much more time than would be required for the preliminary sketch. Where a number of details are to be put on a drawing, as shown on Plate 8, provision must be made for the proper marking of each piece, as well as the necessary figure lines. If the detail is of a small piece, like some of the screws on this plate, much more space should be allowed than would be sufficient for the piece itself, as the title alone may require more space than the drawing of the piece. If provision for each part, and the necessary views, be not made before the drawing is begun, the draftsman may discover, when it is too late to rectify the mistake, that some piece has been omitted, thus requiring an entire sheet to be devoted to this piece, or the re-drawing of the whole.
 
14. Number and Arrangement of Views. This discussion of the arrangement of a sheet leads to the consideration of the number and arrangement of views. The only rule for guidance in this matter, is to draw tis few views as shall be consistent with the interpretation of the idea, but enough to accomplish this fully. In the valve drawing, Plate 3, one view would suffice for the complete representation of the object, two being shown here to simplify the problem for the student. In Plate 9, two views are barely sufficient for the ready reading of the di-awing. The character of the view has also much to do with the number of views required; thus, a sectional representation will frequently give more information than two outside, or full, views.