This chapter is intended to deal chiefly with the special application of drawing to the practice of wood and metal work, and as an aid to the effective teaching and demonstrating of the above subjects. It is presumed that a knowledge of elementary practical plane and solid geometry, drawing from the cast (light and shade), freehand and model drawing has been acquired. The special kinds of drawing necessary to pupils when dealing with the subject of handcraft are as illustrated on plate opposite. Fig. 1 shows a tee joint in orthographic projection, meaning right projection, from orthos (right) and gonia (an angle), or the geometrical representation of solids upon a plane surface in front and side elevation, and plan. The representation may be full size, as in the case of a working drawing, as to scale. The procedure is exactly the same as in solid geometry. An elevation (see Fig. 1) is first drawn on an XY line, each point being numbered as a, b and a', b'. Projectors are then dropped from these points below the XY line into the horizontal plane. The line ab is next drawn, then the thickness lines aa and bb. A side view is projected as shown, thus completing the three views required of the object. The next system-called pictorial projection (see Fig. 2)-is a simple method of obtaining an approximately correct pictorial view of a given object. An elevation is first drawn as for orthographic projection, then lines are projected from the elevation at any convenient angle (300 or 45° are most suitable), the real thickness of the object is divided, and one-half is transferred to the thickness lines. The points obtained are then joined up and the back surface is represented. It should be noted that the latter lines are always parallel to their corresponding lines in the face side. Fig. 3 represents oblique projection; it differs from the former method only in one particular, viz. real lengths are marked on the projected lines instead of half-lengths. Angles of 30° and 450 are also suitable for this system. Compass lines and curves can be represented also when occurring in a model, involving the use of ordinates or guide lines. It is a satisfactory method for representing joints, small models, and constructive detail, and has the added advantage of showing three dimensions in a drawing, viz. length, width, and thickness. The use of the latter system is not recommended for large objects, having the disadvantage of giving an unpleasant tilted-up effect to the drawing. Various details are shown in this work, drawn as described. Isometric projection, from isos and metric, meaning equal measure, is particularly well suited for the representation of architectural and woodworking objects, these usually being composed of right-angled solids, or with their adjacent planes at right angles. This system was invented by Professor Farish. The lines BA, DA, and CA constitute the isometric axes, and all lines coincident with a parallel to these axes are drawn true length upon the picture. To represent the front elevation of the tee piece in isometric projection, the width of the stem should be marked from the regulating point A. A perpendicular is then erected parallel to the axis DA; the lines of the head are then drawn parallel to BA and DA respectively; thickness lines of the object illustrated are drawn parallel to AC, then true lengths are marked upon them, and when connected they are of course parallel to the axis DA. Curves, simple mouldings, and bevels may also be represented. The uses and limitations of the latter system are similar to those of oblique projection. Working Drawings constitute an important part of handcraft subjects; they are really an extended application of the principles embodied in the first example, and reference to the drawings in this book will suggest suitable arrangements of the views. Perspective is a branch of drawing knowledge based upon geometry, and it demands much study and practice in theoretical perspective shadow projection in order to become a proficient draughtsman. From the standpoint of teacher or student requiring perspective as an aid to effective expression of ideas or for purposes of graphic demonstration, a strictly accurate method is not absolutely essential. Architects' perspective is a much simpler system, and, although only approximately correct, it suffices for practical purposes. It may be divided into three kinds, of which the first is illustrated in Fig. 5, which also shows the key to the system. The scale is first decided upon, and then the elevation, side view, and plan may be drawn. Next a ground line is drawn (see key diagram), then the height or eye line at a distance of 5 ft. above the ground line, this representing the average height of a spectator's eye. The plan should then be transferred, the front corner touching the eye line, with the front line making an angle of 40° with it, the adjacent side of course subtending an angle of 50°. A station point is next decided, its distance from the GL depends upon the size of the object to be projected; it may be immediately below the nearest corner of the object, but not necessarily. Vanishing points must next be decided, the large diagram showing a suitable method of obtaining same; one line is drawn at an angle of 40° with the SP and another at 50° as shown. These are produced until they cut the HL. Angles of 300 and 6o° may also be adopted, but the angle subtended by the vanishing lines should in all cases be 900. The position of the legs is shown in the plan; a set square is placed on the drawing, touching one point of the plan and also the SP, then short projectors can be drawn until they cut the HL. From these points of intersection perpendiculars are dropped. The first to be so drawn is the nearest line of the leg in plan; this must equal in length the elevation, and upon this line all heights for horizontal lines are measured. Both diagrams show the method of completing the drawing. Decorative features are added freehand; in the case of large curves ordinates may be employed for greater accuracy. It will be noticed from the views that all lines below the eye run in an upward direction, whilst those above the eye, as in Fig. 6, run downwards. A lantern is shown as an example in the latter diagram. The preparatory system is the same as that employed for the table. In both cases it is assumed that the distance of the spectator from the object is similar, therefore the nearest point in the plan coincides with a point on the HL. Projectors are drawn as before, and the necessary perpendiculars are drawn above instead of below the HL. The nearest point of the lantern should be about 7 ft. 6 in. from the SP, and a perpendicular raised from this provides the necessary line for preliminary measurements, which should also in this case be transferred from the elevation. If shading the completed line-drawing is desired, a good effect can be obtained by shading certain parts. The light has been considered in the diagrams to proceed from a position coincident with the left-hand VP. Those parts of the object farthest from the light are therefore strongly shaded, whilst the top receives a full measure of lighting and is left clear. The front of the table receives about half the light and is shaded as half-tone. Various media can be employed for this part of the work. With wash or colour drawings the washes should be made up in various depths of tone value; with pen and ink work the distance of the lines one from another is increased or decreased according as light or dark tones are required, as is also the case if pencils are used. The rendering of small objects in perspective is facilitated if a large scale is employed, as for example, the book-rest shown in Fig. 7. The real height is approximately 8 in.; this has been multiplied by 8, giving an assumed height of 3 ft. 4 in., which enables the object to be drawn by the method previously described. This is particularly well suited for the representation of small handcraft models, including handles, finger plates, bread platters, etc.
Fig. 5.-Diagrams illustrating method of showing objects in perspective when placed below the eye line.