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Watchmakers' Hand-Book

Part I,
ARITHMETIC, GEOMETRY, DRAWING, ETC
Page 3

GEOMETRICAL DRAWING.

      19. An elementary knowledge of the art of drawing, an ability to represent the outlines of objects by simple lines, is of the first importance to the watchmaker.

      Such a design is obtained by projecting on to one plane all the visible points of the object represented.

      Projection on a vertical plane gives an elevation; the object is looked at from one side.

      Projection on to a horizontal plane produces a plan; the object is observed from above, thus giving a bird's-eye view.

Part I Fig 4

      The projection of a point on a vertical or horizontal plane is the foot of the perpendicular, from the given point on to the plane. Assume the line n m (fig. 4), to be fixed in space; its horizontal projection will give c d, and its vertical projection, r s.

      Miscellaneous details. When one portion of the object to be represented is found to pass behind other pieces so that it cannot be seen, the continuation is frequently indicated by dotted lines.

      Surfaces that are situated in planes one behind the other are shaded, the more deeply according as they are farther back. This shading is produced by a number of parallel lines which may be vertical or horizontal.

      Parts that are in relief are indicated by projected shadows, or by increasing the thickness of a line that would cast a shadow.

      In order to distinguish the several shadows or to emphasize the lines by which they are separated, it is a very usual, though not invariable practice to assume the light to be coming from the left hand upper corner.

Part I Fig 5

      When drawing a square in relief, such as abcd (fig. 3), the lines cd,bd, will be made darkest; but if it is a recess, the lines ab,ac should be brought into prominence by means of dark lines.

      These several directions will be found useful when a hole, any cavity, a pin, a round object, etc., has to be depicted, as in (fig. 5). As a general rule, the thick lines should indicate the position at which a shadow would form, the light being assumed to fall on the drawing in the manner indicated above.

Part I Fig 6

      A section shows a body as it would appear if cut in two, and one portion removed in order to expose the interior, as in (fig. 6). A section is indicated by a series of parallel lines drawn close together and at an inclination of about 45° to the vertical.

      In order to leave more room for important details, or to show objects that are situated behind, a piece is often proken off by an irregular line, as shown in that drawing.

      Lines formed by a series of detached points sometimes serve as a means of associating several figures representing the same object looked as in different directions.

      20. Tracing and transferring. These two operations are resorted to when it is required to obtain one or more copies of a picture or design already drawn.

      Tracing consists in laying a piece of tissue or other translucent paper over the drawing and copying it by following over the lines that are visible with a pencil. Or ordinary paper can be used for the purpose, providing it is not too thick, if the picture be placed against the pane of a window or, what is more convenient, on a sheet of glass used as a desk and illuminated from below. When either sheet of paper is too thick to allow sufficient light to pass, one or other of the methods of transferring indicated below must be resorted to.

      21. This operation consists in reproducing a tracing on a separate sheet of paper or on metal that is to be engraved. Either of the following methods may be adopted:

      (1.) The picture to be transferred is fixed to a table or drawing board if tracing paper is to be used, or to a sheet of glass if only ordinary paper is available. The lines are then traced with a black lead pencil that must not be too hard. When this is finished it is laid, face downwards, on a sheet of white paper, taking care that both sheets are so fixed that they shall not slip. Apply pressure to the upper surface by tapping with a small pad made on purpose and, at the same time, gently rubbing. Experience will very soon show how hard the pad should be. Now remove the tracing, still taking care to avoid any slipping, and a faint reproduction of the design will be found on the lower sheet of paper. It is only necessary to follow over the lines with India ink. The figures will be reversed, but a transfer with it in the original direction may be obtained by inverting the picture and laying it on glass so as to make a reverse tracing.

      (2.) Lay the picture on a desk or drawing board and trace it with ink on a very transparent sheet of paper. When the ink is dry, invert the tracing and blacken the back with a No. 2 pencil. Now lay the tracing, with the ink side uppermost, on a sheet of clean paper, taking care to avoid slipping, and go over the several lines with an agate or metal style, avoiding excessive pressure on account of the risk of tearing the paper. On removing the upper sheet an impression will be found not revered. Go over all the lines with India ink and clean the paper with India-rubber or stale bread.

      Observations. The choice of paper and pencil is not a matter of indifference. All kinds of paper do not receive an impression equally well, neither do all pencils transfer with equal facility. The Faber pencil No. 3, will generally be found best suited to such work.

      In preparing drawings which you desire to preserve, as drawings of escapements, etc., a good quality of light weight bristol board will be found more desirable than the best drawing papers. White wedding bristol, about two-ply in thickness, answers admirably, and India ink lines drawn upon it will not spread as they often do on drawing papers. The prepared liquid India ink now on the market are superior to any you can prepare by grinding the sticks.

      22. To transfer an engraved design. This method is available when it is desired to obtain an impression, for example, of the engraved surface of a watch case.

      Procure some of the inks used by copper-plate engravers, or, in its absence, ordinary stencil ink may be used. Taking a small quantity on the end of the finger, tap it on the surface of a glass plate, in order that the ink may be distributed, leaving only a small quantity evenly spread over the finger: tap with the finger thus prepared over the watch case long enough to make sure that all the surface in relief has received some ink; take a piece of writing paper and, after slightly moistening it, spread it over this surface. Lay above this a piece of paper folded in four and pass over it in all directions any round body, such as a small tool handle, and with some pressure; then raise the papers without allowing them to slide.

      If the operation has been carefully performed a very clear impresion will thus be obtained of the engraved surface. The relief will be black and the hollows white, but, of course, the figure is reversed like that in a looking-glass. If required in the right directrion it must be traced through to the other side of the paper.

Submitted by: Samuel Kirk (##)

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