粗切削与精切削（中英）

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There are two kinds of cuts in machine- shop work called, respectively, the "roughing cut" and the "finishing cut". When a piece is "roughed out", it is quite near the shape and size required, but enough metal has been left on the surtace to finish smooth and to exact size."

Generally speaking, bars of steel, forging, castings, etc. are machined to
the required shape and size with only one roughing and one finishing cut. Sometimes, however, certain portions of a piece may require more than one roughing cut. Also, in some jobs, fot example, when great accuracy is not needed, or when a comparatively small amount of metal must be removed, a finishing cut may be all that is required.

The roughing cut, to remove the greater part of the excess material, should be reasonably heavy, that is, all the machine, or cutting tool, or work, or all three, will stand. So the machinist's purpose is to remove the excess stock as fast as he can without leaving, at the same time, a surface too torn and rough, without bending the piece if it is slender, and without spoiling the centers.

The finishing cut, to make the work smooth and accurate, is a finer cut. The emphasis here is refinement - very sharp tool, comparatively little metal removed, and a higher degree of accuracy in measurement.

Whether roughing or finishing, the
machinist must set the machine for the given job. He must consider the size and shape of the work and the kind of material, also the kind of tool used and the nature of the cut to be made, then he proceeds to set the machine for the correct speed and feed and to set the tool to take the depth of cut desired.



机械工厂的切削加工有两种，分别称为“粗切削”和“精切削”。工件经“粗切削”后，十分接近所要求的形状和尺寸，但加工表面仍留有足够的金属余量，以供精加工，使工件表面光洁、尺寸准确。

一般地说，钢质棒料、锻件、铸件等只经一次粗切削和一次精切削即可达到所要求的形状和尺寸。不过，有时工件的某些部位可能需要不止一次的粗切削。有些加工，如精度要求不高或需要切除的金属量较小，也可能只需一次精切削。

粗切削因为要去除大部分的余料，切削力量肯定是相当大的，这就意味着，整个机器、刀具、工件或这三者都要能承受得了。机加工工人的目的是尽可能快地切除余料，而留下的加工表面又不能太粗糙，细长的工件不能抗弯，也不能损坏顶尖。

精切削是使工件表面光滑、尺寸准确，因而是一种更精细的切削。精加工强调的是精度——使用非常锋利的刀具，切除的金属量较少，测量时的精密度要求较高。

无论是粗切削还是精切削，机加工工人都必须按给定的工作来调好机床，必须考虑工件的大小和形状，材料的种类，刀具的种类，以及行将切削的性质。然后开始把机床调到正确的转速和进刀量，调好刀具使其达到要求的切削深度。