DOE-HDBK-1016/2-93Engineering Fabrication,ENGINEERING FABRICATION, CONSTRUCTION,Construction, and Architectural DrawingsAND ARCHITECTURAL DRAWINGSRev. 0Page 11PR-06Figure 8 Example of TolerancingBecause tolerances allow a part or the placement of a part or feature to vary or have a range,all of an object's dimensions can not be specified. This allows the unspecified, and therefor non-toleranced, dimension to absorb the errors in the critical dimensions. As illustrated in Figure8 (A) for example, all of the internal dimensions plus each dimension's maximum tolerance addsup to more than the specified overall dimension and its maximum tolerance. In this case thelength of each step plus its maximum tolerance is 1 1/10 inches, for a maximum object lengthof 3 3/10 inches. However the drawing also specifies that the total length of the object cannotexceed 3 1/10 inches. A drawing dimensioned in this manner is not correct, and one of thefollowing changes must be made if the part is to be correctly manufactured.To prevent this type of conflict, the designer must either specify different tolerances for eachof the dimensions so that the length of each smaller dimension plus its maximum error adds upto a value within the overall dimension plus its tolerance, or leave one of the dimensions off,as illustrated in Figure 8 (B) (the preferred method).
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