毕业设计英文翻译1

Center Lathe

4.1 INTRODUCTION

Lathe is the oldest machine tool invented, starting with the Egyptian tree lathes. In the Egyptian tree lathe, one end of the rope wound round the workpiece is attached to a flexible branch of a tree while the other end is pulled by the operator, thus giving the rotary motion to the workpiece. This primitive device has evolved over the last two centuries to be one of the most fundamental and versatile machine tools with a large number of uses in all manufacturing shops.

The principal form of surface produced in a lathe is the cylindrical surface. This is achieved by rotating the workpiece while the single point cutting tool removes the material by traversing in a direction parallel to the axis of rotation and termed as turning as shown in Fig.4.1.The popularity of the lathe due to the fact that a large variety of surfaces can be produced.

Different types of lathes are used in manufacturing shops. Some of them are:

(a)Centre lathe

(b)Tool room lathes

(c)Special purpose lathes

(d)Copying lathe

(e)Gap bed lathe

(f)Capstan and turret lathes

(g)Automatic lathes

The centre lathe is the most common lathe which derives its name from the way a workpiece is clamped by centres in a lathe, though this is not the only way in which the job is mounted. This is sometimes also called as engine lathe in view of the fact that early lathes were driven by steam engines. This is generally used for more general applications and thus the construction of the machine tool is more rigid.

The tool room lathe is generally meant for applications of tool making, where the accuracy desired is much higher than that is normally required for general production

work. Also the range of sizes and materials handled would normally be large. Thus the machine would have a higher range of speeds and feeds along with greater rigidity. The range of accessories and attachments would generally be larger.

Special purpose lathes are developed from the centre lathe to cater to special forms of application which cannot be handled by the conventional centre lathe.

Capstan and turret lathes and automatic lathes cater to high rate production and thus are used for special application purposes. These lathes have the special feathers to help in improving the production rate and also work unattended if necessary, They have been discussed in detail in the next chapter.

4.2 CONSTRUCTIONAL FEA TURES OF A CENTRE LA THE

A typical centre lathe is shown in Fig.4.2.The headstock is towards the left-most end on the spindle. The spindle is hollow and is sufficiently rigid to provide accurate rotary motion and maintains perfect alignment with the lathe axis. A live centre fits into the Morse taper in the spindle hole for the purpose of locating the workpiece axis.

The main gear box provides the necessary spindle speeds considering the range of materials to be turned in the lathe. The headstock also houses the feed gear box to provide the various feed rates and thread cutting ranges.

The tailstock is towards the right-most end on the bed, which provides a tailstock spindle for the purpose of locating the long components by the use of centers. The tailstock is movable on the inner guideways provided on the bed to accommodate the different lengths of workpieces, It also serves the purpose of holding tools such as centre drill, twist drill, reamer, etc. for making and finishing holes in the components which are located in line with the axis of rotation.

The third major element in the lathe mechanism is the carriage which provides the necessary longitudinal motion to the cutting tool to generate the necessary surfaces. This also houses the cross-slide for giving the motion (cross feed) to the cutting tool in a direction perpendicular to the axis of rotation, the compound slide which provides an auxiliary slide to get the necessary special motion for specific surfance generations and the tool post which allows for the mounting of the cutting tool.