Page 99 - Engineering drawing from first principles using AutoCAD

92 Engineering drawinq /1"0111 first principles

Motor housing

Fig. 3.18(a) shows the dimensions of a fan motor housing. An isometric presentation is
required for the component and the method is shown in Fig. 3.18(b). There are three
basic parts which can be drawn separately and then assembled. The main case profile
requires an elliptical shape to be converted into isometric projection. Three ordinates are
illustrated as typical examples of the method but more ordinates are required near to the
top of the curve for accuracy. Connect the points on the curve with a polyline of O.4mm
thick and use Fit on the Edit Polyline feature to improve the profile. The bottom
semicircle will appear as an isometric ellipse. The cylinder for the motor cover is best
drawn away from the elliptical fan housing and then moved into position after hidden
detail has been removed. This reduces the number of construction lines on the same spot.

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(b)

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(c)

Figure 3.18 (continued)