机械外文翻译中英文

翻译：

英文原文

Definitions and Terminology of Vibration

vibration

All matter-solid, liquid and gaseous-is capable of vibration, e.g. vibration of

gases occurs in tail ducts of jet engines causing troublesome noise and sometimes

fatigue cracks in the metal. Vibration in liquids is almost always longitudinal and can

cause large forces because of the low compressibility of liquids, e.g. popes conveying

water can be subjected to high inertia forces (or “water hammer”) when a valve or tap

is suddenly closed. Excitation forces caused, say by changes in flow of fluids or

out-of-balance rotating or reciprocating parts, can often be reduced by attention to

design and manufacturing details. Atypical machine has many moving parts, each of

which is a potential source of vibration or shock-excitation. Designers face the

problem of compromising between an acceptable amount of vibration and noise, and

costs involved in reducing excitation.

The mechanical vibrations dealt with are either excited by steady harmonic

forces ( i. e. obeying sine and cosine laws in cases of forced vibrations ) or, after an

initial disturbance, by no external force apart from gravitational force called weight ( i.

e. in cases of natural or free vibrations). Harmonic vibrations are said to be “simple” if

there is only one frequency as represented diagrammatically by a sine or cosine wave

of displacement against time.

Vibration of a body or material is periodic change in position or displacement

from a static equilibrium position. Associated with vibration are the interrelated

physical quantities of acceleration, velocity and displacement-e. g. an unbalanced

force causes acceleration (a = F/m ) in a system which, by resisting, induces vibration

as a response. We shall see that vibratory or oscillatory motion may be classified

broadly as (a) transient; (b) continuing or steady-state; and (c) random.

Transient Vibrations die away and are usually associated with irregular

disturbances, e. g. shock or impact forces, rolling loads over bridges, cars driven over

pot holes-i. e. forces which do not repeat at regular intervals. Although transients are

temporary components of vibrational motion, they can cause large amplitudes initially

and consequent high stress but, in many cases, they are of short duration and can be

ignored leaving only steady-state vibrations to be considered.

Steady-State Vibrations are often associated with the continuous operation

of machinery and, although periodic, are not necessarily harmonic or sinusoidal. Since

vibrations require energy to produce them, they reduce the efficiency of machines and

mechanisms because of dissipation of energy, e. g. by friction and consequent

heat-transfer to surroundings, sound waves and noise, stress waves through frames

and foundations, etc. Thus, steady-state vibrations always require a continuous energy

input to maintain them.

Random Vibration is the term used for vibration which is not periodic, i. e.

has no made clear-several of which are probably known to science students already.

Period, Cycle, Frequency and Amplitude A steady-state mechanical

vibration is the motion of a system repeated after an interval of time known as the

period. The motion completed in any one period of time is called a cycle. The number

of cycles per unit of time is called the frequency. The maximum displacement of any

part of the system from its static-equilibrium position is the amplitude of the vibration

of that part-the total travel being twice the amplitude. Thus, “amplitude” is not

synonymous with “displacement” but is the maximum value of the displacement from

the static-equilibrium position.

Natural and Forced Vibration A natural vibration occurs without any

external force except gravity, and normally arises when an elastic system is displaced

from a position of stable equilibrium and released, i. e. natural vibration occurs under

the action of restoring forces inherent in an elastic system, and natural frequency is a

property of he system.

A forced vibration takes place under the excitation of an external force (or

externally applied oscillatory disturbance) which is usually a function of time, e. g.

in unbalanced rotating parts, imperfections in manufacture of gears and drives. The

frequency of forced vibration is that of the exciting or impressed force, i. e. the

forcing frequency is an arbitrary quantity independent of the natural frequency of the

system.

Resonance Resonance describes the condition of maximum amplitude. It

occurs when the frequency of an impressed force coincides with, or is near to a

natural frequency of the system. In this critical condition, dangerously large

amplitudes and stresses may occur in mechanical systems but, electrically, radio and

television receivers are designed to respond to resonant frequencies. The calculation

or estimation of natural frequencies is, therefore, of great importance in all types of

vibrating and oscillating systems. When resonance occurs in rotating shafts and

spindles, the speed of rotation is known as the critical speed. Hence, the prediction

and correction or avoidance3 of a resonant condition in mechanisms is of vital

importance since, in the absence of damping or other amplitude-limiting devices,

resonance is the condition at which a system gives an infinite response to a finite

excitation.

Damping Damping is the dissipation of energy from a vibrating system, and

thus prevents excessive response. It is observed that a natural vibration diminishes in

amplitude with time and, hence, eventually ceases owing to some restraining or

damping influence. Thus if a vibration is to be sustained, the energy dissipated by

damping must be replaced from an external source.

The dissipation is related in some way to the relative motion between the

components or elements of the system, and is caused by frictional resistance of some

sort, e.g. in structures, internal friction in material, and external friction caused by air

or fluid resistance called “viscous” damping if the drag force is assumed proportional

to the relative velocity between moving parts. One device assumed to give viscous

damping is the “dashpot” which is a loosely fitting piston in a cylinder so that fluid

can flow from one side of the piston to the other through the annular clearance space.

A dashpot cannot store energy but can only dissipate it.

Basic Machining Operations and Machine Tools

Basic Machining Operations

Machine tools have evolved from the early foot-powered lathes of the Egyptians and

John Wilkinson’s boring mill. They are designed to provide rigid support for both the

workpiece and the cutting tool and can precisely control their relative positions and

the velocity of the tool with respect to the workpiece. Basically, in metal cutting, a

sharpened wedge-shaped tool removes a rather narrow strip of metal from the surface

of a ductile workpiece in the form of a severely deformed chip. The chip is a waste

product that is comsiderably shorter than the workpiece from which it came but woth

a corresponding increase in thickness of the uncut chip. The geometrical shape of the

machine surface depedns on the shape of the tool and its path during the machinig

operation.

Most machining operations produce parts of differing geometry. If a rough cylindrical

workpiece revolves about a central axis and the tool penetrates beneath its surface and

travels parallel to the center of rotation, a surface of revolution is producedand the

operation is called turning. If a hollow tube is machined on the inside in a similar

manner, the operation is called boring. Producing an external conical surface of

uniformly varying diameter is called taper turning. If the tool point travels in a path

of varying radius,a contoured surface like that of a bowling pin a can be produced; or,

if the piece is short enough and the support is sufficiently rigid, a contoured surface

could be produced by feeding a shaped tool normal to the axis of rotation. Short

tapered or cylindrical surfaces could also be contour formed.

Flat or plane surfaces are frequently required. The can be generated by adial turning

or facing, in which the tool point moves normal to the axis of rotation. In other cases,

it is more convenient to hold the workpiece steady and reciprocate the tool across it in

a series of straight-line cuts with a crosswise feed increment before each cutting

stroke. This operation is called planing and is carried out on a shaper. For larger

pieces it is easier to keep the tool stationary and draw the workpiece under it as in

planing. The tool is fed at each reciprocation. Contoured surfaces can be produced by

using shaped tools.

Multiple-edged tools can also be used. Drilling uses a twin-edged fluted tool for holes

with depths up to 5 10times the drill diameter. Whether the dril turns or the workpiece

rotates, relative motion between the cutting edge and the workpiece is the important

factor. In milling operations a rotary cutter with a number of cutting edges engages the

workpiecem which moves slowly with respect to the cutter. Plane or contoured

surfaces may be produced, depending on the geometry of the cutter and the type of

feed. Horizontal or vertical axes of rotation ma be used, and the feed of the workpiece

may be in any of the three coordinate directions.

Basic Machine Tools

Machine tools are used to produce a part of a specified geometrical shape and precise

size by removing metal from a ductile materila in the form of chips. The latter are a

waste product and vary from long continuous ribbons of a ductile material such as

steel, which are undesirable from a disposal point of view, to easily handled

well-broken chips resulting from cast iron. Machine tools perform five basic

metal-removal processes: turning, planing, drilling, milling, and frinding. All other

metal-removal processes are modifications of these five basic processes. For example,

boring is internal turning;reaming,tapping, and counterboring modify drilled holes and

are related to drilling; hobbing and gear cutting are fundamentally milling operations;

hack sawong and broaching are a form of planing and honing; lapping, superfinishing,

polishing, and buffing are avariants of grinding or abrasive removal operations.

Therefore, there are only four types of basic machine tools, which use cutting tools of

specific controllable feometry: , s, ng machines, and g

machines. The frinding process forms chips, but the geometry of the barasive grain is

uncontrollable.

The amount and rate of material removed by the various machining processes may be

large, as in heavy truning operations, or extremely small, as in lapping or

superfinishing operations where only the high spots of a surface are removed.

A machine tool performs three major functions: rigidly supports the workpiece or

its holder and the cutting tool; 2. it provedes relative motion between the workpiece

and the cutting tools; 3. it provides a range of feeds and speeds usually ranging from 4

to 32 choices in each case.

Speed and Feeds in Machining

Speeds feeds, and depth of cut are the three major variables for economical machining.

Other variables are the work and tool materials, coolant and geometry of the cutting

tool. The rate of metal removal and power required for machining depend upon these

variables.

The depth of cut, feed, and cutting speed are machine settings that must be established

in any metal-cutting operation. They all affect the forces, the power, and the rate of

metal removal. They can be defined by comparing them to the needle and record of a

phonograph. The cutting speed is represented by the velocity of the record surface

relative to the needle in the tone arm at any instant. Feed is represented by the

advance the needle radially inward per revolution, or is the difference in position

between two adjacent grooves.

Turning on Lathe Centers

The basic operations performed on an engine lathe are illustrated in Fig. Those

operations performed on extemal surfaces with a single point cutting tool are called

turning. Except for drilling, reaming, and tapping, the operations on intermal surfaces

are also performed by a single point cutting tool.

All machining operations, including turning and boring, can be classified as roughing,

finishing, or semi-finishing. The objective of a roughing ooperation is to remove the

bulk of the material sa repidly and as efficiently as possible, while leaving a small

amount of material on the work-piece for the finishing operation. Finishing operations

are performed to btain the final size, shape, and surface finish on the workpiece.

Sometimes a semi-finishing operation will precede the finishing operation to leave a

small predetermined and uniform amount of stoxd on the work-piece to be removed

by the finishing operation.

Generally, longer workpieces are turned while supported on one or two lathe centers.

Cone shaped holes, called center holes, which fit the lathe centers are drilled in the

ends of the workpiece-usually along the axis of the cylindrical part. The end of the

workpiece adjacent to the tailstock is always supported by a tailstock center, while the

end near the headstock may be supported by a headstock cener or held in a chuck. The

headstock end of the workpiece may be held in a four-jar chuck, or in a collet type

chuck. This method holds the workpiece firmly and transfers the power to the

workpiece smoothly; the additional support to the workpiece priovided by the chuck

lessens the tendency for chatter to occur when cutting. Precise results can be obtained

with this method if care is taken to hold the workpiece accurately in the chuck.

Very precise results can be obtained by supporting the workpiece between two centers.

A lathe dog is clamped to the workpiece; together they are driven by a driver p;ate

mounted on the spindle nose. One end of the workpiece is machined; then the

workpiece can be turned around in the lathe to machine the other end. The center

holes in the workpiece serve as precise locating surfaces as well as bearing surfaces to

carry the weight of the workpiece and to resist the xutting forces. After the workpiece

has been removed from the lathe for any reason, the center holes will accurately align

the workpiece back in the lathe or in another lathe,or in a cylindrical grinding machine.

The workpiece must never be held at the headstock end by both a chuck and a lathe

center. While at first thought this seems like a quick method of aligning the workpiece

in the chuck, this must not be done because it is not possible to press evenly with the

jaws against the workpiece while it is also supported by the center. The alignment

provided by the center will not be maintained and the pressure of the jaws may

damage the center hole, the lathe center,and prehaps even the lathe spindle.

Compensatng or floating jaw chucks used almost exclusively on high production work

provice an exception to the statements made above. These chucks are really work

drivers and cannot be used for the same purpose as ordinary three or four=jaw chucks.

While very large diameter workpieces are sometimes mounted on two centers, they

are preferably held at the headstock end by faceplate jaes to obtain the smooth power

transmission; moreover, large lathe dogs that are adequate to transmit the power not

generally available, although they can be maed as a special. Faceplate jaws are like

chuck jaws except that thet are mounted on a faceplate, which has less overhang from

the spindle bearings than a large chuck would have.

Boring

The boring operation is generally performed in two steps; namely, rough boring and

finish boring. The objective of the rough-boring operation is to remove the excess

metal rapidly and efficiently, and the objective of the finish-boring operation is to

obtain the desired size, surface finish, and location of the hole. The size of the hole is

obtained by using the trial-cut procedure. The diameter of the hole can be measured

with inside calipers and outside micrometer calipers. Basic Measuring Insteruments,

or inside micrometer calipers can be used to measure the diameter directly.

Cored holes and drilled holes are sometimes eccentric wwith respect to the rotation of

the lathe. When the boring tool enters the work, the boring bar will take a deeper cut

on one side of the hole than on the other, and will deflect more when taking this

deeper cut,with the result that the bored hole will not be concentric with the rotation

of the work. This effect is corrected by taking several cuts through the hole using a

shallow depth of cut. Each succeeding shallow cut causes the resulting hole to be

more concentric than it was with the previous cut. Before the final, finish cut is taken,

the hole should be concentric with the rotation of the work in order to make certain

that the finished hole will be accurately located.

Shoulders, grooves, contours, tapers, and threads are bored inside of holes. Internal

grooves are cut using a tool that is similar to an external grooving tool. The procedure

for boring internal shoulders is very similar to the procedure for turning

shoulders are faced with the boring tool positioned with the nose

leading, and using the cross slide to feed the tool. Internal contours can be machined

using a tracing attachment on a lathe. The tracing attachment is mounted on the cross

slide and the stylus follows the outline of the master profile plate. This causes the

cutting tool to move in a path corresponding to the profile of the master profile plate.

Thus, the profile on the master profile plate is reproduced inside the bore. The master

profile plate is accurately mounted on a special slide which can be precisely adjusted

in two dirctions, in two directionsm, in order to align the cutting tool in the correct

relationship to the work. This lathe has a cam-lick type of spindle nose which permits

it to take a cut when rotating in either direction. Normal turning cuts are taken with

the spindle rotating counterclockwise. Thie boring cut is taken with the spindle

revolving in a clockwise direction, or “backwards”. This permits the boring cut to be

taken on the “back side” of the bore which is easier to see from the operator’sposition

in front of the lathe. This should not be done on lathes having a threaded spindle nose

because the cutting force will tend to unscrew the chuck.

中文翻译

振动的定义和术语

振动

所有的物质---固体，液体和气体-----都能够振动，例如，在喷气发动机尾部导管中产生的气体振动会发出令人讨厌的噪声，而且有时还会使金属产生疲劳裂缝。液体中的振动总是纵向的，而且由于液体的可压缩性低，这种振动还会产生很大的力。例如，当输水管道的阀门或水龙头突然关闭时，管道会遭受很大的惯省性力的作用（或称为水击）。诸如，由于液体流动状态改变或者转动，往复运动零件推动平衡所产生的激振力，一般可以通过对各零件的精心设计和制造来使用权其得到降低。一台常见的机器中有许多运动零件，每个零件都是潜在的振动源或冲击激振源。设计人员需要处理好振动与噪声的允许值与降低激振所需要的费用之间的关系。

所讨论的振动或者由稳态的谐振力引起的振动（也就是服从正弦或余弦定律的强迫振动），或者是在初始扰动之后，除了被称为重量的重力之外，没有其他外力引起的振动（也就是自然或自由振动的情况）。如果仅用一个频率的正弦或余弦波图形就可表示位移与时间的关系，谐振就被认为是“简单的”。

一个物体或一种材料在振动时，它相对于静平衡位置的位置变化或位移是周期性的。与振动有关的物理量是相互关联的加速度，速度和位移。例如，一个不平衡的力在系统中造成的加速度（a =F/m）会因为系统的抵抗而引起振动作为响应。可以看到，振动或者振荡大致可以分为三类：（1）瞬态的，（2）连续的或稳态的，（3）随机的。

瞬态振动是逐渐衰减的，而且通常与不规则的扰动有关，例如，滚动载荷通过桥梁，汽车通过坑洞，也就是在确定的期间内不重复的力。尽管瞬态振动是振动的暂时性成分它们能够产生大初始振幅和引起高的应力。在大多数情况下，它们持续的时间很短，因而人们可以将其忽略不计而只考虑稳态振动。

稳态振动通常和机器的连续运转在关，而且尽管这种振动是周期性的，但不一定是谐振或正弦振动。由于需要能量才能产生振动，因此，振动消耗了能量，降低了机器和机构的效率。能量的消耗有多种方式，磨擦和随后将所产生的热传到周围，声波和噪声，以及通过机架与基础的应力波等到。因此稳态振动总是需要连续的能量输入来维持其存在。

随机振动是一个用来描述非周期性振动的术语。也就是说，这种振动不是周期性变化的，是不定期地进行重复的。

在下面段落中，对一些与振动有关的术语和定义加以明确，其中一些可能是理科学生都已经清楚了的。

周期，循环，频率和振幅。 稳态机械振动是系统在一定时间范围内的重复运动，该时间范围被称为周期。在任何一个周期内所完成的运动，被子称为一个循环。每个单位时间内的循环数目被称为频率。系统任何部分离开它的静平衡位置的最大位移就是该部分振动的振幅，总的行程是振幅的两倍。因此，“振幅”并不是“位移”的同义词，而是距离静平衡位置的位移最大值。

自由振动和强迫振动。除了重力以外，在没有任何其他作用时产生的振动称为自由振动。通常一个弹性系统离开它的稳定平衡位置后且被松开时，这个系统就会产生振动。也就是说，自由振动是在弹性系统固有弹性恢复力的作用下产生的，而固有频率则是系统的一个特性。

强迫振动是在外力的激励（或者外部的振荡性干扰）下产生的。这个激励或干扰通常是时间的函数。例如，在不平衡的转动部件中，或者是在有缺陷的齿轮和传动装置中就会产生这种振动。强迫振动的频率就是激振力或者外部施加的力的频率。也就是说，强迫振动的频率是一个与系统固有频率没有关系的任意量。

共振。共振描述了最大振幅的状况。当外力的频率与系统的固有频率相同或相近时就会产生共振。在这种临界条件下，机械系统中出现具有危险性的在振幅和高应力。但是，电学上，收音机和电视机的接收器则被设计成在共振频率时工作。因此，在所有各种振动或振荡系统中，计算或者估计系统的固有频率是非常重要的。

阻尼。阻尼是振动系统中能量被消耗的现象，它可以防止过量的响应。可以观察到，自由振动的振幅会随时间而衰减，因而，振动最终将由于某些限制或阻尼的影响而停止。因此，如果要使振动持续下去，一定要有外部的能源对由于阻尼而耗散的能量进行补充。

能量耗散以某种方式与系统的部件或元件之间的相对运动有关，它是由于某种类型的磨擦引起的。例如，在结构中，材料内部的磨擦和由空气可液体阻力等造成的外部磨擦被称为“粘性”阻尼，在这里假定阻力与运动部件之间的速度成

正比。一种能够提供黏性阻尼的装置被称为“阻尼器”。它是由一个缸体与一个活塞松驰配合形成的，液体能够从活塞的一端通过环形间隙流到另一端。阻尼器不能存储能量，仅能消耗能量。

基本的加工工序和机床

基本的加工工序

机床是从早期的埃及人的脚踏动力车床和约翰·威尔金森的镗床发展而来。它们用于为工件和刀具两者提供刚性支承并且可以精确控制它们的相对位置和相对速度。基本上讲，在金属切削中一个磨尖的楔形工具以紧凑螺纹形的切屑形式从有韧性工件表面去除一条很窄的金属。切屑是废弃的产品，与其工件相比相当短但是比未切屑的部分有相对的增加。机器表面的几何形状取决于刀具的形状以及加工操作过程中刀具的路径。

大多数加工工序生产出不同几何形状的部件。如果一个粗糙的柱形工件绕中心轴旋转而且刀具穿破工件表面并沿与旋转中心平行的方向前进，就会产生一个旋转面，这道工序叫车削。如果以类似的方式加工一根空心管的内部，则这道工序就叫镗削。制造一个直径均匀变化的锥形外表面叫做锥体车削。如果刀具尖端以一条半径可变的路径前进，就可以制造出像保龄球杆那种仿形表面；如果工件足够短而且支承具有足够的刚性，仿形表面可以通过进给一个垂直于旋转轴的仿形工具来制造。短的锥面或柱面也可以仿形切削。

常常需要的是平坦的或平的表面。它们可以通过径向车削或端面车削来完成，其中刀具尖端沿垂直于旋转轴的方向运动。在其他情况下，更方便的是固定工件不动，以一系列直线式切削的方式往复运动刀具横过工件，在每次切削行程前具有一定横向进给量。这种龙门刨削，和牛头刨削是在刨床上进行的。大一些的工作很容易保持刀具固定不动，而像龙门刨削那样在其下面拉动工件，在每次往复时进给刀具。仿形面可以通过使用仿形刀具来制造。

也可以使用多刃刀具。钻削使用两刃刀具，孔深可达钻头直径的5～10倍。不管是钻头转动还是工件旋转，切削刃与工件之间的相对运动是一个重要因数。在铣削作业中，有许多切削刃的旋转铣刀与工件相接合，这种工件相对铣刀运动缓慢。根据铣刀的几何形状和进给的方式，可以加工出平面和仿形面。可以使用水平或垂直旋转轴，工件可以沿三个坐标方向中的任意一个进给。

基本的机床

机床用于以切屑的形式从韧性材料上去除金属来加工特殊几何形状和精密尺寸的部件。切屑是废品，其变化形状从像钢这样的韧性材料的长的连续带状屑到铸铁形成的易于处理、彻底断掉的切屑，从处理的观点来讲，不想要长的连续带状屑。机床完成5种基本的金属切削工艺：车削、刨削、钻削、铣削和磨削。其它所有金属切削工艺都是这5种基本工艺的变形。例如：镗削是内部的车削；铰削、锥体车削和平底锪孔则修改钻孔，与钻削有关；滚齿与切齿是基本铣削作业；弓锯削和拉削是刨削和珩磨的一种形式；而研磨、超精加工、抛光和磨光则是磨削和研磨切屑作业的各种变化形式。因此，仅有4种使用专用可控几何形状的刀具的基本机床：1.车床2.刨床3.钻床4.铣床。磨削工艺形成碎屑，但是磨粒的几何形状不可控制。

不同的加工工艺切屑的材料的量和速度可能大，如大型车削作业；或者极小，如研磨或超精加工作业，只有表面高出的点被去除。

机床完成3种主要功能：1.刚性支承工件或工件夹具以及切削刀具；2.提供工件与切削刀具之间的相对运动；3.提供了一定范围的速度和进给，通常每种情况有4～32种选择。

加工中的速度和进给

切割速度、进给和深度是经济加工的3个主要变量，其它变量还有工件和工具的材料、冷却剂以及切削刀具的几何形状。金属切削的速率和加工所需的功率就取决于这些变量。

切割深度、进给和切削速率是在任何金属切削作业中必须都建立的机器设置。它们都影响切削力、功率和对金属切削的速率。可以通过把它们与留声机的唱针和唱片相比较给出其定义。切削速度由任意时刻唱片表面相对于拾音器支臂内部的速度来表示；进给由唱针每圈径向向内的前进量或者由两个相邻槽的位置差来表示。切削的深度是唱针进入唱片的量或者是槽的深度。

切削

在普通车床上完成的基本车削工序，那些在外表面上用单刃刀具完成的工序叫车削。除钻削、铰削和锥体车削外，在内表面的作业也由单刃刀具完成。

包括车削和镗削在内的所有加工工序都可以分为粗加工、精加工和半精加工。粗

加工工序的目的是尽可能迅速且高效地去除大量的材料，在工件上只留下少量的材料给精加工工序。精加工工序用以获得工件最终的大小、形状和表面光洁度。有时，在精加工工序前进行半精加工作业以便在工件上留下少的、预定期和均匀量的原材料供精加工去除。

通常，较长的工件是在一个或两个车床顶尖的支承下进行车削的。用于安装车床顶尖的锥形孔叫作顶尖孔，它是在工件的端部钻出的—通常沿着柱形部件的轴心。与尾架邻近的工件端部总是由尾架顶尖支承，而挨着主轴箱的一端则由主轴箱顶尖支承或装在卡盘内。工件的主轴箱一端可以装在一个四爪卡盘内。这种方法牢固地夹持工件并且把功率平稳地传送到工件；由卡盘提供的额外支承减少了车削作业时发生震动的倾向。如果仔细地将工件精确固定在卡盘上，用这种方法将可以获得精密的结果。

通过将工件支承在两个顶尖之间可以获得非常精密的结果。一个车床夹头夹在工件上；然后由安装在主轴前端的拨盘一起带动。先加工工件的一端，然后可以在车床上将工件转过来加工另一端。工件上的顶尖孔是用作精确定位面以及承受工件重量和抵抗车削力的轴承面。在工件由于任何原因被从车床上拆下后，顶尖孔可以精确地将工件装回车床或另一台车床，或都装在一台外圆磨床上。工件永远也不要同时通过卡盘和车床顶尖安装在主轴箱端。虽然乍一想这似乎是一种在卡盘中对正工件的快捷办法，但是一定不能这么做，因为当工件同时同顶尖支承时不可能将工件均匀地压在爪上。由顶尖获得的对正不能维持而且爪的压力可能损坏顶尖孔、车床顶尖甚至车床主轴。几乎被独自用在大量生产工件上的补偿或浮动爪式卡盘是上述的一个例外。这些卡盘是自动偏心夹紧卡盘不能起到普通三爪或四爪卡盘同样的作用。

直径非常大的工件虽然有时安装在两个顶尖上，但是最好用花盘爪把它们固定在主轴箱端以获得流畅的动力传输；此外，可以把它们制造成专用部件，但是一般没有提供足够大的车床夹头来传输动力。除了是安装在花盘上以外，花盘爪像卡盘爪，其主轴轴承上的外伸要比大卡盘上的也要少一些。

镗削

镗削工序一般分两步完成，即粗镗和精镗。粗镗工序的目的是快速，高效地去除多余的金属；而精镗工序的目的是获得所需的尺寸、表面光洁度和孔的位置。孔

的尺寸通过使用试切割程序而获得。孔的直径可以用内卡尺和外千分卡尺测量。测量仪表或内千分卡尺可用于直接测量直径。

型心孔和钻的孔有时相对于车床的旋转是偏心的。当镗孔工具进入工件时，镗杆在孔的一边的切口比另一边深，当采用这一深切口时就会更偏斜了，结果镗的孔不与工件旋转同心。这一影响通过利用浅切口在整个孔加工中进行几次线切口来纠正。因为每个浅切口使形成的孔比使用先前切口形成的孔更加同心。在完工前，进行精加工，孔应该与工件的旋转同心以确保完工孔会精确定位。

肩、沟槽、轮廓、锥度和螺纹也应该在孔内镗出。内槽是用与外部开槽工具相拟的工具切削。镗削内槽的步骤非常类似于肩部的步骤。大的肩部使用前导装置定位的镗孔工具进行刮削，使用横向滑板进给刀具。内部轮廓使用车床上的描摹附件加工。仿形板附件安装在横向滑板上，靠模指跟随标准剖面样板的轮廓线运动。这使刀具对应于标准剖面样板的轮廓线的路径进行移动。这样标准剖面样板的轮廓就在孔内得到复制。标准剖面样板精确安装在一个专用的滑板上，滑板可以在两个方向上进行精确调整以使刀具与工件以正确的关系对正。这台车床有一个偏心夹型的主轴前端，允许在任意一方向旋转时进行切削。正常的车削世削是在主轴逆时针转动时进行的；镗削切削是在主轴顺时针方向或“向后”转动时进行的。这允许在孔的“后侧”进行镗削切削，在车床前面，从操作者的位置易于看到孔。在具有螺纹主轴前端的车床上不应这么做，因为切削力会旋松卡盘。