Each machine tool discussed in previous chapters represents a basic cutting machine. Some particular cutting operation, such as turning, drilling（钻）, milling（铣）, or grinding（磨）, can be performed on each. They can be highly productive. Nevertheless（然而） each perform only a single function or at best a limited number of functions. Most parts require several different operations in their fabrication – one surface is rough machined, another superfinished（超级压光）, a hole drilled and a slot（槽） milled, all on the one part. Thus, the tool must be changed, the workpiece（工件） indexed（分度） and shafted from one machine to another. This results in much expenditure of labor and much nonproductive down-time.
One way of improving this situation is to design a machine tool on which more than one kind of cutting operation can be performed. Another is to enable to machine to perform its operation successively or even simultaneously(同时) on the same workpiece without any intermediate（中间的） handling（操作）. A third is automatic gauging（自动检验） of machined features（机械特征） with an arrangement for ejecting the finished part and inserting another blank. A final refinement is to incorporate feedback controls that regrind and even reset tools, or make other adjustments as directed automatically by gauge readings.
Complete automation of a machine tool includes all above. This, the machine is equipped not only to perform its cutting automatically but also to “decide” what adjustments must be made to machine work according to specifications（规范）.
Broadly then, automatic machining comprises cutting where all tool and work-material movements are so actuated that duplicate(完全相同的) parts may be made repeatedly without continuous attention. If cutting operations are automatic but an operator is needed to remove finished parts or reload or reset the machine, semi-automatic operation is generally said to exist. In either case, machine time is reduced and dimensional precision（尺寸精度） often improved.
Vocabulary
1.represent t. 讲述；代表；体现
2.nevertheless conj. 然而；不过
3.fabrication n. 制作
4.superfinish v. 超级压光
5.slot n. 槽；缝
6.gage n. 计量器; v. 度量；计量
7.index v. 转位
8.shaft v. 装以轴；转动；利用
9.successively ad. 接连地；连续地
10.simultaneously ad. 同时；一并地
11.eject vt. 推出；弹出
12.blank n. 坯件；毛坯
13.refinement n. 精加工；改进
14.incorporate v. 采用；转换角度
15.broadly ad. 广泛地；广阔地
16.duplicate a. 完美的 n. 复制品
