It should be emphasized that dimensioning must be performed with the user of the drawing very much in mind. In the case of the finished bearing housing shown in Fig. 14.35 two different production processes are involved in its manufacture: namely casting and machining of the component. It is sometimes preferable to produce two separate drawings, one to show the dimensions of the finished casting and the other to show the dimensions which are applicable to the actual machining operation. Figure 14.34 shows a suitable drawing for the casting patternmaker. Allowances are made for machining and also for the fact that the casting will shrink when it cools. The machinist will take the rough casting and remove metal to produce the finished component, all other surfaces having a rough finish. Figure 14.35 shows the required dimensions for
Figure 14.33 shows the method of dimensioning. Note that, in both cases, the depth of spotface is just sufficient to remove the rough surface of the casting over the 40 mm diameter area.
machining. Note that the bore of the casting is required to be finished between the two sizes quoted for functional purposes.
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