毕业论文外文翻译-尺寸公差.docVIP

Dimensional Tolerance The manufacture of machine parts is founded on the engineering drawing．Everyone engaged in manufacturing has a direct or indirect interest in understanding the meaning of the drawings on which the entire production process is established． The engineer in industry is constantly faced with the fact that no two machine Darts can ever be made exactly the same.He learns that the small variations that occur in repetitive production must he considered in the design 80 that the tolerances placed on the dimensions will restrict the variations to acceptable limits .The tolerances provide zones in which the outline of finished part must lie. Proper tolerancing practice ensures that the finished product functions in its intended manner and operates for its expected life. A designer is well aware that the cost of a finished product can increase rapidly as the tolerances on the components are made smaller．Designers are constantly admonished to us the widest tolerances possible. Situations may arise，however，in which the relationship between the various tolerances required for proper functioning has not been fully explored．Under such conditions the designer is tempted to specify part tolerances that ale unduly tight in the hope that no difficulty will arise at the time of assembly．This is obviously an expensive substitute for a more thorough analysis of the tolerancing situation． The allocation of proper production tolerances is therefore a most important task if the finished product is to achieve its intended purpose and yet be economical t0 produce．The size of the tolerances，as specified by the designer，depends on the many conditions pertaining to the design as well as on past experience with similar products if such experience is available.A knowledge of shop processes and machine capabilities is of great assistance in helping to determine the tolerances in the most effective maimer. A revision of the design may be called for if the toleranc