1、附录 A 英文原文LatheDescription The purpose of a lathe is to rotate a part against a tool whose position it controls.It is useful for fabricating parts and/or features that have a circular cross section.The spindle is the part of the lathe that rotates.Various workholding attachments such as three jaw chu
2、cks,collets,and centers can be held in the spindle.The spindle is driven by an electric motor through a system of belt drives and/or gear trains.Spindle speed is controlled by varying the geometry of the drive train.The tailstock can be used to support the end of the workpiece with a center,or to ho
3、ld tools for drilling,reaming,threading,or cutting tapers.It can be adjusted in position along the ways to accomodate different length workpices.The ram can be fed along the axis of rotation with the tailstock handwheel.The carriage controls and supports the cutting tool.It consists of:A saddle that
4、 mates with and slides along the ways.An apron that controls the feed mechanisms.A cross slide that controls transverse motion of the tool(toward or away from the operator).A tool compound that adjusts to permit angular tool movement.A toolpost T-slot that holds the toolpost.Fundamentals of Mechanic
5、al DesignMechanical design means the design of things and systems of a mechanical naturemachines,products,structures,devices,and instruments.For the most part mechanical design utilizes mathematics,the materials sciences,and the engineering-mechanics sciences.The total design process is of interest
6、to us.How does it begin?Does the engineer simply sit down at his desk with a blank sheet of paper?And,as he jots down some ideas,what happens next?What factors influence or control the decisions which have to be made?Finally,then,how does this design process end?Sometimes,but not always,design begin
7、s when an engineer recognizes a need and decides to do something about it.Recognition of the need and phrasing it in so many words often constitute a highly creative act because the need may be only a vague discontent,a feeling of uneasiness,or a sensing that something is not right.The need is usual
8、ly not evident at all.For example,the need to do something about a food-packaging machine may be indicated by the noise level,by the variation in package weight,and by slight but perceptible variations in the quality of the packaging or wrap.There is a distinct difference between the statement of th
9、e need and the identification of the problem which follows this statement.The problem is more specific.If the end is for cleaner air,the problem might be that of reducing the dust discharge from power-plant stacks,or reducing the quantity of irritants from automotive exhausts.Definition of the probl
10、em must include all the specifications for the thing that is to be designed.The specifications are the input and output quantities,the characteristics and dimensions of the space the thing must occupy and all the limitations on these quantities.In this case we must specify the inputs and outputs of
11、the box together with their characteristics and limitations.The specifications define the cost,the number to be manufactured,the expected life,the range,the operating temperature,and the reliability.There are many implied specifications which result either from the designers particular environment o
12、r from the nature of the problem itself.The manufacturing processes which are available,together with the facilities of a certain plant,constitute restrictions on a designers freedom,and hence are a part of the implied specifications.A small plant,for instance,may not own cold-working machinery.Know
13、ing this,the designer selects other metal-processing methods which can be performed in the plant.The labor skills available and the competitive situation also constitute implied specifications.After the problem has been defined and a set of written and implied specifications has been obtained,the ne
14、xt step in design is the synthesis of an optimum solution.Now synthesis cannot take place without both analysis and optimization because the system under design must be analyzed to determine whether the performance complies with the specifications.As stated previously,the purpose of machine design i
15、s to produce a product which will serve a need for man.Inventions,discoveries and scientific knowledge by themselves do not necessarily benefit people;only if they are incorporated into a designed product will a benefit be derived.It should be recognized,therefore,that a human need must be identifie
16、d before a particular product is designed.Installing a Cutting Tool Lathe cutting tools are held by tool holders.To install a tool,first clean the holder,then tighten the bolts.The tool post is secured to the compound with a T-bolt.The tool holder is secured to the tool post using a quick release lever.Positioning the Tool In order to move the cutting tool,the lathe saddle and cross slide can be moved by hand.There are also power feeds for these axes.Procedures vary from machine to machine.A thi
