Tolerances, ContinuedBasic shaftThe basic shaft system is a system of fits in which the design size of the shaftsystemis the basic size and the allowance applies to the hole.Figure 3-40 illustrates the basic shaft system.Figure 3-40.—The basic shaft system.In the illustration, the maximum shaft size is the basic size. To obtain theminimum hole diameter, assume an allowance of .003 inch and add that tothe basic shaft size.Arbitrarily selecting a tolerance of .002 inch, add the tolerance to the holeand shaft to obtain the maximum hole (1.505 inches) and the minimum shaft(1.498 inches). The clearance fit is the difference between the smallest hole(1.503 inches) and the largest shaft (1.500 inches) or .003 inch. Themaximum clearance fit is the difference between the largest hole (1.505inches) and the smallest shaft (1.498 inches) or .007 inches.Determine the minimum hole size of an interference fit by subtracting theallowance (.003 inch) from the basic shaft size (1.500 inches) or 1.497inches).To convert basic shaft size to basic hole size, add the allowance for aclearance fit or subtract it for an interference fit.3-45
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