CBSE Book Class 11 Engineering Graphics Sections Of Solids

SECTIONS OF SOLIDS

5.1 INTRODUCTION

We have studied about the orthographic projections in which a 3 dimensional object is detailed in 2-dimension. These objects are simple. In engineering most of the machines are extremely complicated. They have various parts inside. And we have to show the details of inside, so the engineers adopt a technique called ‘sectioning’. The objects/ machines are “imagined to be cut” in a particular manner and the interior becomes visible and is shown by a sectional view.Let us take the machine block as shown in Fig. 5.1 Examine the orthographic views of thisblock. They have many hiddenlines (showing invisible surfaces/edges) but don’t give a clear idea about the inside details.

So a portion/part of the object nearer to the observer is imagined to be cut and is removed away from the cutting plane, known as the ‘section plane’, to show the interior (inside) details more clearly. As can be seen in Fig. 5.2 The view (projection) of the remaining cut portion of the object is known as the sectional view. Refer to 5.2 (a) The cut/exposed surface, known as the section is represented by thin equidistant inclined lines (section lines) known as hatching. (Fig. 5.2 (a) & (b)).

5.1.1 Uses of Sections

We have come to know why sections are needed. Let us know some more details which are as follows :

– Sectioning helps the engineers/technicians considerably in clarifying the interior details (solid, hollow, etc.) These details are otherwise quite complicated to be shown & dimensioned by outside views & hidden lines.

– It may also be used to show a small cross section (perpendicular to axis) of a machine part as shown in Fig. 5.3

– It helps in understanding and interpreting the drawings for manufacture of machine parts.

In this chapter, we are going to deal with sections of simple solids which is important to understand the interpenetration of surfaces (where combination of different solids are used to make a machine part).

Fig. 5.3 Cross-section of Simple Solids

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