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Machine parts are manufactured so they are interchangeable.In other words,each part of a machine or mechanism is made to a certain size and shape so it will fit into any other machine or mechanism of the same type.To make the part interchangeable,each individual part must be made to a size that will fit the mating part in the correct way.It is not only impossible,but also impractical to make many parts to an exact size.This is because machines are not perfect,and the tools become worn.A slight variation from the exact size is always allowed.The amount of this variation depends on the kind of part being manufactured.For example,a part might be made 1.5 inches in diameter with a variation allowed 0.001 inch,above and below this size.Therefore,the part could be 1.499 to 1.501 inches and still be the correct size.These are known as the limits.The difference between upper and lower limits is called the tolerance. 机器生产零件,所以他们是可以互换的。 换句话说,每一部分机器或机制是一种特定的大小和 形状,它能塞进其他机器或机制相同的类型。 可互使部分换的,每个人都必须做出部分尺寸适 合交配,参加了正确的方法。 它不仅是不可能的,但也不让很多地方到一个精确的尺寸。 这是 因为机器还很不完善,工具磨损。一个稍微变化的大小正好合适总是允许的。这一差异的数 量取决于类型的部分正在制造的。 例如,一个部份可能是使1.5英寸直径变化允许0.001英寸, 上面和下面的尺寸。 因此,部分可能是1.499到1.501英寸,仍然是正确的尺寸。 这些被称为非 限制。区别上下限,叫做宽容。 Quality and accuracy are major considerations in making machine parts.Interchangeable parts require suitable accuracy to fit together.Both of dimensions of parts given on engineering drawings and manufactured dimensions should be exactly the same and fit properly.Unfortunately,it is impossible and unnecessary to make things to an exact shape or dimension.Most dimensions have a varying degree of accuracy and means of specifying acceptable limitations in dimensional variance that an object will tolerate and still have its function. 质量和精度的主要考量使机械零件。 可互换的零件精度要求适当配合。 两个维度的部分工程 图纸制造了尺寸应该完全相同,而且合适。不幸的是,这是不可能的,不必要的做一个确切的 形状和尺寸。 大多数维度有不同程度的准确性和可接受的方式限制规定一个物体在空间方差 会容忍,还有它的功能。 Size usually includes nominal,basic,design,and actual size,etc. 大小通常包括名义、基本设计和实际尺寸等。 Nominal size generally identifies the overall size of an object without any error. 一般公称通径识别物体的总体规模没有任何错误。 Basic size in the size from which the limits of size are derived by the application of allowances and tolerances. 基本尺寸的大小,范围的大小,得出应用津贴和公差。

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