horizontal would be parallel or perpendicular (ornearly so) to a prominent visible outline, the angleshould be changed to 30°, to 60°, or some otherangle. If two adjacent sectioned surfaces areshown, the hatching should be in oppositedirections, as shown in figure 5-34, view B. If stilla third surface is included, it should be hatchedat another suitable angle to make the surfaceclearly stand out separately from the othersurfaces (figure 5-34, view C). Note that thehatching lines on one surface are not permittedto meet those on an adjacent surface.In drawing section lining, use a sharp,medium-grade pencil (H or 2H). Space the linesas uniformly as possible by eye. As a rule,spacing of the lines should be as generous aspossible, yet close enough to distinguish thesectioned surface clearly. For average drawings,space the lines about 3/32 in. or more apart.Diagonal hatching on an auxiliary sectionshould be drawn at 45 degrees to the horizontal,with respect to the section. Figure 5-35 shows thisrule.In a revolution or other view of an object inother than the normal position, the diagonalhatching on a section should be drawn at45 degrees to the horizontal or vertical axis of theobject as it appears in the revolution. Figure 5-36shows this rule.Axonometric ProjectionAxonometric single-plane projection isanother way of showing an object in all threeFigure 5-35.-Diagonal hatching on an auxiliary section.Figure 5-36.-Diagonal hatching on a revolution.dimensions in a single view. Theoretically,axonometric projection is orthographic projectionin that only one plane is used and the projectionlines are perpendicular to the plane of projections.It is the object itself, rather than the projectionlines, that is inclined to the plane of projection.ISOMETRIC PROJECTION AND ISOMET-RIC DRAWING.—Figure 5-37shows a cubeprojected by ISOMETRIC PROJECTION, themost frequently used type of axonometricprojection. The cube is inclined so that all of itssurfaces make the same angle (35°16´) with theplane of projection.As a result of thisinclination, the length of each of the edges shownin the projection is somewhat shorter than theactual length of the edge on the object itself. Thisreduction is called FORESHORTENING. Thedegree of reduction amounts to the ratio of 1 tothe cosine of 35°16´, or 1/0.8165. This means thatif an edge on the cube is 1 in, long, the projectededge will be 0.8165 in. long. As all of the surfacesmake the same angle with the plane of projection,the edges all foreshorten in the same ratio.Therefore, one scale can be used for the entirelayout; hence the term isometric, which literallymeans “one-scale.”Figure 5-38 shows an isometric projection asit would look to an observer whose line of sightwas perpendicular to the plane of projection. Note5-20
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