OF ENGINEERING SPECIFICATIONS AND CONTRACTS, DESIGNED AS A TEXT BOOK AND WORK OF REFERENCE FOR ALL WHO MAY BE ENGAGED IN BY LEWIS M. HAUPT, PROFESSOR OF CIVIL ENGINEERING, TOWNE SCIENTIFIC SCHOOL, UNIVER- "Scientiarum omnium robur instar fascis illius senis; non in singulis bacillis. PHILADELPHIA: PUBLISHED BY J. M. STODDART & CO., 723 CHESTNUT STREET. 1878. Entered according to Act of Congress, A. D. 1878, by L. M. Haupt, in the office of Librarian of Congress, at Washington. SBL .H29 1878 612236 CHAPTER I. THE DRAWINGS. Drawing is the art of representing graphically, Drawing defined. objects or ideals, as they exist or appear to exist. The representation of objects as they exist, Classification. showing their forms, sizes and positions, is included in those subdivisions of the art known as Orthographic Projections, Isometrical Perspective, and Shades and Shadows. The representation of objects as they appear to exist is known as Scenographic Projection, Linear or Aerial Perspective. tive Geometry as a To draw correctly, therefore, involves a thorough Value of Descripknowledge of Descriptive Geometry with its appli- study. cations to the Arts and Manufactures. Its study should be insisted upon in all Technical Schools, as in addition to its direct use, it is particularly valuable in developing the inventive and perceptive faculties, which of all others are most useful to the practical engineer. Form and color. All objects possess two general characteristics form and color; but the color, which serves merely to give variety and expression to the object, is limited by Form, the chief and contained within the form. It is to the latter jects. therefore to which our chief care and attention should be directed in all drawings. characteristic of ob universal, Form is an universal language, and hence the ne- Language of form, cessity of resorting so largely to it in the representation of all tangible and visible objects. It avoids much ambiguity and a multiplicity of words, and is intended in the drawing to be a representation in miniature of the idea or thing to be delineated. The scale is the expression of the ratio of the Scale defined. drawing to the object. The value of a drawing depends, therefore, principally upon the accuracy of its outline, which should be made Simplicity and accuracy of outline, on as large a scale as convenient and not be con- required. fused by a mass of details. To make a complete representation of a solid, at The three projecleast three projections are necessary, the plan, eleva- tions. tion and section, but frequently many more are required, and in complex constructions there should be shown, firstly, the general views of the various parts properly assembled as a whole, either in linear or isometrical perspective or in projection, and secondly, the three or more projections of each of the parts or details, usually on a larger scale. To this latter class belong Working drawings. all "working drawings" which are always made to a scale, and to prevent any mistake which might arise from errors in the drawings, all distances and dimensions should be Dimensions should carefully written upon the parts to which they be marked. belong. The space intended to be embraced by the figures is indicated by dotted arrows extending outward from them, thus: Written dimensions the to be taken as au any thority in cases of doubt. Selecting the scale and preserving its ratio to drawing Should it happen that the dimensions marked do not correspond with the distances given by scale, and it is impossible to determine from source which is correct, preference should be given to the numerals, unless they are manifestly in error, and the work constructed in accordance therewith must be accepted. The scale should be so large that the least dimension may be distinctly represented. It is desirable also to construct it upon the same sheet of constant. paper with the drawing, that it may be subjected to the same variations from changes of temperature, moisture and other causes, and thus the ratio of the two remain constant. A detached scale upon a piece of paper of the same quality will be found very convenient and more accurate than the dividers, Objections to the which are liable to slip or spring back as well as to dividers. injure the drawing. For small measurements the Other scales. diagonal scale is the most accurate. Triangular box-wood scales are also very useful. decimal systems Constructions in Architecture, Machinery or any Decimal and duoworks executed by artisans are usually represented when used. by the duodecimal scales, whilst those for the engineer are ex |