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Chapter 20

INTERPRETATION OF THE VIEWS

A drawing is said to be effective if it contains a minimum of lines and views.The views must be chosen in such a way that they will provide a completeand exact information about the object. The lines in all the views of an objectshould lead to one and only one interpretation. For this, one needs to have

knowledge of drawing conventions, dimensioning techniques, sectioningmethods, and use of notes and notation systems. This chapter explains howto read and interpret a given drawing correctly.

INTERPRETATION FROM ONE VIEW

Many objects can be completely interpreted from one view only. Washers,gaskets, flat sheet metal objects, printed circuit boards (PCBs), etc., are thecommon examples. When only one view is used to describe the object, useof appropriate dimensioning techniques, sectioning methods and notesshould be made to clarify the features of the object, as illustrated in Fig. 20.1.

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INTERPRETATION FROM TWO VIEWS

A majority of the machine components require two views to specify theirshapes completely. In such cases, if only one view is provided, it leads tomisinterpretation.

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In two-view drawings, the choice of the views plays an important role. As astandard practice, FV and TV or FV and SV are drawn. The view whichdisplays the maximum details should be chosen as the FV or TV. For many

objects, as a thumb rule, the view which has maximum dimensions (i.e.,length x width) is chosen as the FV. Once the FV is decided, another viewshould be chosen in such a way that the two views together provide thecomplete information about the object. For illustration, consider an objectshown in Fig. 20.5(a). When viewed in direction X, its FV, TV and SV are seenas in Fig. 20.5(b). For viewing direction Y, the three views will be as in Fig.

20.5(c). A little examination will show that only FV and SV in Fig. 20.5(b) aresufficient to provide a complete idea of the object.

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The objects shown in Fig. 20.7 to Fig. 20.9 represent examples of two-view drawings. In each case, only one interpretation is possible from thegiven two views.

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INTERPRETATION FROM THREE VIEWS

There are a few objects which need three views for complete

understanding. The third view becomes necessary if the object hasdifferent geometries in the three mutually perpendicular faces whichcannot be identified by any two views. Figures 20.10 & 20.11 show theexamples.

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Figure 20.14 & 20.15 explain the necessity of three views to explain someunique features of the objects. These objects cannot be visualizedcorrectly with any two views. The third view is always necessary todetermine the shape of some features of the object.

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Example 20.1 Figure 20.18(a), (c) & (d) show two views of the objects.Draw isometric view(s) of each object considering all possibleinterpretations.

Solution Refer Fig. 20.19(a), (c) & (d) for possible interpretations.

Fig. 20.18

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Fig. 20.19

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Figures 20.20, 20.21 & 20.25 show pictorial views of the objects. Foreach object, state the minimum number of principal views needed todescribe the object completely.

The minimum essential views are

Fig. 20.20: FV and TV Fig. 20.21: FV Fig. 20.25: FV, TV and SV

In each case, the direction for the FV must be chosen properly.

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MISSING VIEWS AND MISSING LINES

A majority of the objects can be completely described from two views.However, the third view may be prepared to ease the visualization. Thethird (or fourth) unknown view is called the missing view. It should benoted that the missing view never adds to the information revealed bythe existing views.

Sometimes, we may have three incomplete views of an object. Theremay be a few missing linesin each view.

The following thumb rules will help draw missing views and missinglines.

1. A point in one view may represent a line or a point in the other view.

2. A continuous straight line in one view may represent a face or a linein the other view.

3. Follow the rules mentioned in Section 14.10 for deciding the hiddenlines.

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Steps in Drawing Missing Views

1. Read carefully the given views. Draw projectors from one view toanother view to decide the correspondences betweenpoints/lines/faces in one view to points/lines/faces in other views.

Also, draw projectors from both the views for the third view. The thirdview must be appropriately located in relation to the existing views.

2. Visualize the object. If multiple interpretations are possible, chooseany one. A small freehand isometric sketch may be drawn if needed.

3. Draw the desired view by locating the required points at theintersections of the projectors. The visualization or the isometric sketchwill help to draw hidden features.

To draw the missing lines, similar steps may be followed.Example20.3 From the FV and TV of an object shown in Fig. 20.27,draw the LHSV.

Solution Follow the steps explained in Fig. 20.28.

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Example 20.5 Figure 20.31 shows the FV and TV of an object. Draw

(i) Sectional FV (along given section)

(ii) TV

(iii) LHSV

Solution Refer Fig. 20.32. First, draw the LHSV as in (c) and then makethe sectional FV as in (d). All the hidden lines and projectors should beremoved from the FV before hatching.

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