KRISHNASAMYCOLLEGE OF ENGINEERING AND TECHNOLOGY

S.Kumarapuram, Cuddalore – 607 109.

Unit-I

1. Explain orthogonal cutting and oblique cutting with its neat sketches and compare.

2. What is the tool life equation and state the factor affecting the tool life?

3. What is machinability? And Explain.

4. Explain the various tool materials.

5. Explain in details about surface finish.6. What are the different type of cutting fluids used in machining process

By fulfilling its main functions, cooling and lubricating the machining site as well as carrying away the chips, modern cutting fluid systems make a substantial contribution to the high performance level of many manufacturing processes. This is achieved by removing process heat from the tool/workpiece contact area by cooling and slowing the progress of heat via lubrication. Not only must excessive heating of the workpieces, which leads to expansion, be avoided, but also temperature load on the cutting tool

material be reduced. The fulfilment of these functions may at first sound simple, but often requires cutting fluid properties which are not readily combined with each other.Types of Cutting Fluids

Unit-II1. Sketch a center lathe and mention various parts.

2. List various types of feed mechanisms and explain briefly about tumbler gear reversing mechanism with a sketch.1. Tumbler gear mechanism 2. Quick change gearbox 3. Tumbler gear- Quick change gearbox 4. Apron mechanism

TUMBLER GEAR MECHANISM

If you see the diagram of tumbler gear mechanism below, E gear is attached to the spindle and known as

spindle gear. The purpose of this gear is to rotate feed rod and lead screw in clockwise direction. A and B

are tumbler gears and are fitted in a bracket. The lever M placed in the bracket can move upward or

downward.

In the construction of the mechanism, gear D is known as stud gear and is connected to lead screw by

intermediate gears. It has two different positions. For position 1, the lever M is in upward position and

gear A connects with stud gear D and spindle gear E. This arrangement will move carriage towards

headstock. On the other hand, if it is in position 2, lever will be in the horizontal position and gear E will

connect with gear B, then B to A and A to D. With this arrangement, lead screw direction will reverse and

this time, it will move in the anti-clockwise direction and carriage will move towards tailstock.

If we want to give manual feed then lever should be in the middle position which will make sure that the

gears are not engaged.

3. Explain taper turning operation in a lathe by a taper turning attachment. Discuss its advantages. Taper turning attachmentTaper cylindrical surface, which is a very common feature of several engineering components, is generally produced in lathes in a number of methods, depending upon length and angle of the tapered position of the job, such as offsetting tailstock, swivelling the compound slide using form tool and combined feed motions. But jobs with wide ranges of length and angle of taper are easily machined by using a simple attachment, called taper turning attachment. Fig. 4.6.1 schematically shows a taper turning attachment where the cross slide is delinked from the saddle and is moved crosswise by the guide block which moves along the guide bar preset at the desired taper angle. Thus, the cutting tool, which is fitted on the cross slide through the tool post and the compound slide, also moves along with the guide black in the same direction resulting the desired taper turning.

4. Explain the methods of taper turning in a lathe.Methods of Taper Turning

The method used for turning a taper depends on the degree, length, location of the taper (internal or external), and the number of pieces to be done.

By swiveling the compound rest By  offsetting the tail stock By taper turning attachment

With any of these methods, the cutting tool must be set exactly on centre with the axis of the workpiece or the workpiece will not be truly conical, and the rate of taper will vary with each cut.

swiveling the compound rest

The compound rest is generally used for turning or boring short steep tapers, but it can also be used for longer, gradual tapers, provided the length of the taper does not exceed the distance the compound rest will move upon its slide. This method can be used with a high degree of accuracy, but is somewhat limited due to the lack of an automatic feed and the length of the taper being restricted to the movement of the slide. The compound rest base is graduated in degrees and can be set at the required angle for taper turning or boring. With this method, it is necessary to know the included angle of the taper to be machined. An included angle is formed by and between two intersecting straight lines. The angle of the taper with the centerline is one-half the included angle and will be the angle that the compound rest is set for.

Calculation

Where D = large diameter d = small diameter L = length of taper

5. Explain the Working principle of capstan and turret lathes.The semiautomatic lathes, capstan lathe and turret lathe are very similar in construction, operation and application. Fig. 4.7.1 schematically shows the basic configuration of capstan lathe and Fig. 4.7.2 shows that of turret lathe.

In contrast to centre lathes, capstan and turret lathes

• are semiautomatic

• possess an axially movable indexable turret (mostly hexagonal) in place of tailstock

• holds large number of cutting tools; upto four in indexable tool post on the front slide, one in the rear slide and upto six in the turret (if hexagonal) as indicated in the schematic diagrams.

• are more productive for quick engagement and overlapped functioning of the tools in addition to faster mounting and feeding of the job and rapid speed change.

• enable repetitive production of same job requiring less involvement, effort and attention of the operator for pre-setting of work–speed and feed rate and length of travel of the cutting tools

• are relatively costlier

• are suitable and economically viable for batch production or small lot production.

• heavy turret being mounted on the saddle which directly slides with larger stroke length on the main bed as indicated in Fig. 4.7.2.

• One additional guide rod or pilot bar is provided on the headstock of the turret lathes as shown in Fig. 4.7.2, to ensure rigid axial travel of the turret head.

• External screw threads are cut in capstan lathe, if required, using a self opening die being mounted in one face of the turret, whereas in turret lathes external threads are generally cut, if required, by a single point or multipoint chasing tool being mounted on the front slide and moved by a short leadscrew and a swing type half nut.

6. Describe a typical single spindle automatic chucking machine.