Figure 5-29.-Use of a revolved section (A-A).block would look if it were revolved 30 degreeson an axis perpendicular to the horizontal plane.Figure 5-28, view B, shows the block as it wouldappear if it were revolved 30 degrees on an axisperpendicular to the vertical plane.REVOLVED SECTIONS.— A common useof the revolution is the revolved section, shownin figure 5-29. At the top of this figure, there isa single projection of a triangular block. You canshow all required information about this block ina two-view projection by including a revolved sec-tion in the front view as shown. You first assumethat the block is cut by a plane perpendicular tothe longitudinal axis.You then revolve theresulting section 90 degrees on an axis per-pendicular to the horizontal plane of projection.SECTIONING TECHNIQUES.— A sectionalview is called for when the internal structure ofan object can be better shown in such a view thanit can by hidden lines. In the upperpart of figure5-30, there is a single-view projection of a pulley.The same object is shown below in a two-viewmulti-view projection. The internal structure ofthe pulley is shown by the hidden lines in the topview.In figure 5-31, the internal structure of thepulley is much more clearly shown by a sectionalview. Note that hidden lines behind the plane ofprojection of the section are omitted in theFigure 5-30.-Internal structure ofhidden lines.an object shown byFigure 5-31.-Internal structure of an object more clearlyshown by sectional view.5-18
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