Tolerance Applications Applications Machinery's Handbook, 31st Edition
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Many factors such as length of engagement, bearing load, speed, lubrication, operating temperatures, humidity, surface texture, and materials must be taken into account in fit selections for a particular application. Choice of other than the preferred fits might be considered necessary to satisfy extreme conditions. Subsequent adjustments might also be desired as the result of experience in a particular application to suit critical functional requirements or to permit optimum manu facturing economy. Selection of a departure from these recommendations will depend upon consideration of the engineering and economic factors that might be involved; how ever, the benefits to be derived from the use of preferred fits should not be overlooked. A general guide to machining processes that may normally be expected to produce work within the tolerances indicated by the IT grades given in ANSI/ASME B4.2-1978 (R2009) is shown in Table 8. Practical usage of the various IT tolerance grades is shown in Table 9. Table 8. Relation of Machining Processes to IT Tolerance Grades IT Grades 4 5 6 7 8 9 10 11 Lapping & Honing Cylindrical Grinding
Surface Grinding Diamond Turning Diamond Boring Broaching Powder Metal sizes Reaming Turning Powder Metal sintered Boring Milling Planing & Shaping Drilling Punching Die Casting
Table 9. Practical Use of International Tolerance Grades For Measuring Tools For Material ITGrades 0101234567891011 12 13 14 15 16 For Fits For Large Manufacturing Tolerances ISO Metric Limits and Fits Based on ISO Recommendation R286, this British Standard BS 4500:1969 is intended to provide a comprehensive range of metric limits and fits for engineering purposes, and meets the requirements of metrication in the United Kingdom. Sizes up to 3,150 mm are covered by the Standard, but the condensed information presented here embraces dimensions up to 500 mm only. The system is based on a series of tolerances graded to suit all classes of work from the finest to the most coarse, and the different types of fits that can be obtained range from coarse clearance to heavy interference. In the Standard, only cylindrical parts, designated holes and shafts are referred to explicitly, but it is emphasized that the recommendations
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