In the preliminary operation of producing a regular mechanical or instrumental drawing, it is necessary to make a "sketch," in pencil, of the object to be represented. The AMERICAN MACHINIST has given in a few words the order to be followed, in effecting the best results; we quote, as follows: "In making a free-hand sketch of an object from the model it is well to observe the following order: Look the model over carefully and determine the number of views necessary to illustrate it fully, drawing the same, free-hand, in their proper relation to each other, on sketching paper. Look the sketch over carefully to see that nothing has been omitted, and put on dimension lines, after which scale the model carefully and put on dimensions. Do not put in the dimensions at the same time the dimension lines are drawn; have all the dimension lines in place before attempting to insert dimensions. "Follow the same order in making the drawing with instruments as was used in making the sketch; that is, draw the views in their proper relation to each other, put in dimension lines, then dimensions, and lastly notes and title. If section drawing is made, do not draw section lines in pencil." POINTS TO BE OBSERVED IN SKETCHING. I. Especial attention is to be paid to outlines— edges of plane surfaces are lines; when a line is made it represents the edge or outside of something. 2. Learn to be accurate before being rapid. 3. A sketch should be intelligible to any one, even if they are unacquainted with drawing. 4. Horizontal and vertical lines and a few curves will enable one to make almost any simple sketch. 5. It must be also remembered in making drawings from actual measurement that the instruments are not in the first place employed; the rough sketch is first made and then it is converted into a drawing. The draughtsman makes a rough sketch entirely by the hand and eye, measures the various parts, and jots down the measurements in his sketch; after this he reduces the whole to the desired scale, and proceeds to make his mechanical drawing. 6. Let the sketch book be the constant companion of the student; it may be advantageously filled with outlines of machine or other work suitable for preservation, to be made into finished drawings, or for reference. Sketches are often valuable for reference as aids in originating new designs. 7. A sketch, when possible, should have all the dimensions written upon it, but 8. Sketches in shop practice should not take the place of working-drawings; the latter have a check upon them in being drawn to a scale-hence the figures written upon them and dimensions by scale must agree. 9. Place title and date on each sketch-no matter how seemingly unimportant-for future reference. IO. Practice sketching at every favorable opportunity. There is no necessity for detail at firstsimply the outlines of the article and its parts. II. Sketch-books, with paper bound in cloth covers, are utilized for bold, off-hand sketches by experienced draughtsmen, but a single sheet of paper, used on both sides, is not unworthy of service in an emergency—or even the blank side of a letter may be available. Sketching-blocks, or paper "pads," 4x6, or more, in size, and containing 48 sheets, are sold by stationers, and are found to be most convenient to have in hand and for practical use. Portfolioenvelopes, made of extra length paper (manila) are useful in filing away sketches and drawings. The size 101⁄2 x 15 is used for United States Patent Office drawings. The function of the pencil-in mechanical drawing —is to make a path for the pen to follow. If it were possible to make a drawing with all its lines ending at the proper place, at the first time, there would be no necessity for using the pencil. One is obliged, however, so to use the pencil that all lines pass beyond the actual ending place, thus making a distinct point for the drawing pen to stop at. The pencil should be pressed to the paper just enough to make a clean, fine line, and no more; once over the path is sufficient, if the line is visible and true. To sharpen drawing pencils, I, use a fine file, after taking off enough of the wood with a knife; 2, make a conical point for the free-hand drawing pencils and a chisel point for ruling and markng distances. Pencil compasses are instruments where one leg is provided with a pencil point. Fig. 209 shows the mode of manipulation of those shown in fig. 180 and fig. 181. The pencil compass is held by the projection above the joint between the thumb and first finger, which enables it to be rotated by a movement of the finger without causing any undue pressure on the points. Should much pressure be applied, there is a tendency to force the point or center through the paper, making an ugly center mark; at the same time the pressure tends to break off the pencil point. These few illustrations from fig. 212 to fig. 219 are made designedly simple, so that they may be utilized in "free-hand" work, for which they are good practice, as well as serving for examples in mechanical drawing. Figs. 212. Figs. 212, showing a spool or bobbin, exhibit three views, viz. : front elevation or plan, and section; both are drawn with, simple lines, the end elevation by circles. Figs. 215 show three views of a file handle; the front view and section are practice for compound curves and curved lines meeting straight ones; all these are capable of being produced by instruments. Moreover, many of the views and illustrations used to instruct and explain machine tools and other devices in other parts of the volume, are drawn so that they may be used also as examples in advanced instrumental practice. This is a "hint" to the diligent and painstaking student worthy of remembering. Fig. 213. Fig. 214. Figs. 213 and 214 are two side views of a hexagon head bolt. Figs. 216 and 217 are a square head bolttwo side views and end view. Figs. 218 and 219 are a front and edge view of a forked or double joint. Figs. 215. |