Three-jaw Chuck and Four-jaw Chuck

In lathe work, workpieces are held either between centres or in a chuck. Sometimes the workpiece is held in a chuck at one end and supported by a centre at the other.

Several types of chucks are available in metal machining. The three-jaw universal and four-jaw independent types are most commonly used in lathe work. They are designed to hold and revolve the workpiece.

The three-jaw universal chuck is used to hold cylindrical work. The chucking is done quickly, as the three jaws move in and out together and automatically centre the work. This type of chuck is accurate when new. It loses its accuracy as the jaws become worn.

To hold workpieces of irregular shapes, we often use a four jaw chuck instead of a three- jaw chuck. Its accuracy is not affected by wear, because each jaw can be adjusted independently. The jaws do not move simultaneously.

Cutting Tools

The metal cutting tool separates chips from the workpiece in order to cut the part to the desired shape and size. There is a great variety of metal cutting tools. Each of them is designed to perform a particular job or a group of metal cutting operations in an efficient manner. For example, a twist drill is designed to drill a hole which has a particular size, while a turning tool may be used to turn a variety of cylindrical shapes.

There are three basic types of metal cutting tools: single-point tools, multiple-point tools, and abrasives. A single-point metal cutting tool has a single cutting edge and is used for turning, boring, shaping, and planing. The most common machine tool that employs the single-point cutting tool is the engine lathe. Multiple-point tools have two or more cutting edge's such as drills, reamers, and milling cutters. The cutting edge is that part of the tool where cutting is actually done. Grinding wheels are an example of abrasive cutting tools. Each grinding wheel has a lot of abrasive grains which act as very small cutting tools.

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金工车间实践

在金工车间实践中我们使用各种机床。车床、钻床、龙门刨床，牛头刨床、铣床和磨床是基本的机床。

车床车削圆柱形工件。车削过程中，工件旋转的同时切削刀具正对着工件进刀。钻床用来钻孔，龙门刨床和牛头刨床用来制造平滑表面。铣床用转刀切削各种形状的工件。磨床用来提高工件的精确度和改善其表面光洁度。

车床的部件

车床在金工车间实践中既很常见又很有用，它有五个重要部件：床身、床头箱、尾架、拖板和进刀箱。

床身是车床的基础部件，它是一个刚性结构。床头箱、尾架和拖板都装在车床床身上。进刀箱在床头箱下面。

铣床

在现代金工车间实践中，我们使用铣床来代替牛头刨床。

铣床有许多种。然而，大多数都是很类似的。升降台式铣床就是最普通的一种。

大多数升降台式铣床的台板都可以作三种运动，即纵向运动、播向运动和垂直运动。某些铣床还可作旋转运动。

最常见的三种升降台式铣床是水平铣床、垂直铣床和万能铣床。水平铣床由下列重要部件组成：床身、升降台、滑动座架、横臂和心轴等。

轴承和润滑 

机床由许多机床部件组成。转轴就是一种最普通最重要的部件。

转轴在某种支承中转动，我们把这些支承叫做轴承。轴承的功用是使转轴平稳地旋转。

轴承有许多种：有套筒轴承、滚珠轴承、滚柱轴承等。我们在不同的场合使用不同的轴承。

磨擦会给运动以阻碍，而润滑会减少磨擦力。因此，恰当的润滑可保护轴承并使运动平滑。不同类型的轴承要求不同的滑油和滑脂。低速轴承采用滑脂，高速轴承要用轻油。滑脂会给运动一些阻滞。

强力磨削

磨削是一种非常重要的金属机加工方法。实际上在每个金工车间里都会有磨床。然而，在不久以前，磨削还只是一种精密加工方法。我们只用磨床对工件进行研磨和抛光。

现在我们也用磨床来切削工件将其加工成形。人们称这种加工方法为强力磨削。强力磨削机床既有采用砂轮的又有采用磨带的。

强力磨削是一种新的磨削方法，几年前刚刚采用。强力磨削同其他机加工方法相比有几个优点。用它切削金属的速度很快，而且加工成本低。强力磨削机床需要的夹具也比较少，而且既能进行粗切削，又能进行精加工。