Classify the different types of lathes. Illustrate the Kinematic system of centre lathe and explain its method of working. State the different machining operations that are usually done in centre lathe. Different types of machining tools:

• Lathes: used to produce cylindrical jobs, internal and external cylindrical surface rod like.

• Drilling machine: cylindrical holes are originated or some time existing hole is enlarged. These are small machines - not that very big holes are made.

• Shaping machines: primitive machine produces flat surfaces and the flat surface can be horizontal, vertical, inclined (They are becoming gradually obsolete)

• Planning machines: also produce flat surfaces like shaping machines but planning machines are made for big jobs, large size of work pieces.

• Slotting machine: basically a vertical shaping machine where the cutting tool reciprocates vertically and it makes internal surfaces say holes or slots or key ways in holes etc. These slotting machines are also not very widely used for batch of mass production only for repair and maintenance work slotting machines are often used in small scale industries.

• Milling machines: used for making flat surfaces - vertical, horizontal, inclined flat surfaces resulting in say grooves, slots some time they are used for parting a piece into two parts. Also used in machining a form (cutting the teeth of gear, threads).

• Boring machines: similar to drilling machines - can be you know vertical type (smaller size) or of horizontal type (large size for the large jobs). Boring machines are normally used for enlarging and existing hole or making a hole accurately in dimension.

• Hobbing machines: used for mass production of gear teeth e.g. teeth of external gears can be cut in large quantity very fast.

• Gear shaping machine: another gear teeth cutting machine (both external and internal gear teeth, internal and external teeth of spline shafts) can be cut. Slightly less productive than hobbing, but produces better quality.

• Broaching machines: used for making flat surface or other than flat surface, for making holes or key way, small gears in spline shafts etc. Broaching tool is very expensive, process is very fast and the quality of the product is good.

• Grinding machines: slow process of metal removal, used only for high accuracy and finish particularly when the works material is very hard cannot be done by machining.

LATHES: Lathes - most common and widely used machine tools

- most primitive machine tool and most versatile. Hence, lathes have been this can be classified in number of ways:

1. According to configuration basic shape or standing: - Horizontal lathes: Most of the lathes are horizontal axis (for ergonomic convenience - the height of

the centre should be at the operator’s waist height so that he can comfortably and conveniently work on the machine.

- Vertical lathes: normally big sized and are kept vertical. Main purpose to it is that it occupies less floor space. For ergonomic convenience, the chucks are kept under the ground so that the worker can work conveniently. They are used for large swing like boring mill and are not very common.

2. According to the purpose of use: single, special or general purpose use.

- General purpose use: very versatile for wide range of materials, size of workpiece, types of machining operations. e.g. centre lathes.

- Single purpose use: for only single or at max. two types of operation. e.g. facing lathes (large diameter short length disc types jobs are faced), roll turning lathes (rollers of rolling mills are finished by turning operations) etc.

- Special purpose use: a definite number and type of operations are done repeatedly on only one type of workpiece (blank). e.g. gear blank machining lathe.

3. According to size and capacity: - Small (light duty): less power (~ 2.2kW); used for small and easily machinable jobs.

- Medium (medium duty): most common; power within ~ 11kW.

- Large (heavy duty): upto ~120kW. bigger jobs, rigid and high speed machine tools.

- Mini or Micro lathes: tiny lathes used for precision machining of very small jobs (e.g. swiss type automatic lathe, micro CNC lathes). May be of size 4-6 inches long or even 1 cm cube (for mini lathes for wrist watch parts manufacturing).

4. According to the degree of automation: (Automation is a system or a device or a mechanism that enables very quick production, easy production with huge amount of jobs with consistently high accuracy.)

Handling operations (mounting of job and cutting tool, speed/feed/depth of cut adjustment, cutting fluid adjustment – basically operations which are non productive)

Processing operations (facing, turning, boring etc.)

Degree of automation will be decided by to what extent the handling operations are done in mechanized way e.g. all handling operations done manually, then non –automatic.

- Non Automatic: all handling operations manual. e.g. centre lathes.

- Semi-automatic: half handling operations automatic. Capstan lathes, turret lathes.

- Automatic: almost all operations automatic. e.g. single spindle automatic lathes, swiss automatic lathes. (machines are compact but complex in shape and design; push button type, very fast production rate, high maintenance cost)

5. According to the type of automation: - Fixed automation: Conventional or Hard automation. Automation is achieved by incorporating lot

of additional devices (mechanical device even electronic device, electrical device, electromechanical device, hydraulic device, computers etc.) to the system. It is called fixed or hard automation because if there have been change in the job or the product then lot of changes have to be incorporated into the machine. Changeover cost is very high. e.g. single spindle automatic lathes.

- Flexible automation: when batch production is required (the products size shape or category changes frequently). So the machine should be capable to cope up with the change over of the job from one design to another. Flexible automation can easily cope up with the change. This is very modern and suitable for batch production for low change over cost. e.g. CNC lathes.

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6. According to the job configuration: - Bar type lathe: rod like slender blank being held in a collet

- Chuck type lathe: discs type jobs (cylindrical) being held in chucks. e.g. blanks of gears, pulleys, shafts etc.

- Housing type lathes: complex shaped (odd type jobs) are mounted on a large face plate ( it has a number of slots in radial and tangential directions). The face plate is mounted on the lathe spindle and odd shaped jobs are fixed by clamping. Not very common, used only for few occasions and complex shaped jobs.

7. According to precision or process capability: (rate of production and accuracy)

- Ordinary: common lathes (dimensional accuracy varies from 10 to 50 microns).

- Precision lathes: capable of high dimensional accuracy but are expensive.

8. According to the number of spindles:

- single spindle: most lathes are of this type - multi spindle (2, 4, 6, max. 8): used for large and fast production of simple shapes and sizes

(e.g. bearing races).

Centre lathe and lathe components:

It is the most commonly used lathe. The main components of this lathe are: Bed: supports all major components of the lathe. It is made of gray or nodular CI for rigidity. It is provided with guide-ways for the movement of the carriage (saddle). Carriage: The lathe carriage serves the purpose of supporting, guiding and feeding the tool against the job during operation. It consists of: Saddle: it is that part of the carriage which slides along the bed guide-ways and supports the cross slide, compound rest and the tool post. Cross slide: it is mounted on top of the saddle and always moves perpendicular to the axis of the spindle (work piece). It facilitates the movement of the tool perpendicular to the work piece. It can be operated manually or by the cross feed screw or by power through the apron mechanism.

Compound rest / tool rest: it is mounted on the cross slide. It consists of - swivel plate (graduated in degrees and helps in swivelling the compound slide and tool post to any angle in the horizontal plate); and compound slide (helps small movement in horizontal direction by the compound rest feed screw). Tool post: topmost part of carriage and holds the tool. Apron: it hangs in front of the carriage and houses a number of gear trains. It consists of a clutch mechanism (used to transmit motion from the feed rod via the gear trains to the carriage and cross slide); and split half nut (closing this nut engages the leadscrew with the carriage and moves the whole carriage during thread cutting). Headstock: is fixed to the bed and houses motors, pulleys, V-belts and gear trains that supply power to the spindle at various rotational speeds. The headstocks have a hollow spindle which are attached to the work piece holding devices such as chucks, collets etc. The work holding devices constitute the live centre. Tailstock: is generally used to hold the work piece from the other end and constitutes the dead centre. It is held on the guide-ways provided on the bed. Sometimes, a tool post is placed instead of the regular tailstock where in drill bits, reamers, boring tools are held to conduct the drilling, reaming, boring operations respectively. Machining Operations done in a Centre Lathe: Facing, Rough and Finish Turning, Chamfering (cutting off/smoothening the edges), Shouldering (making a step along the diameter of the cylinder), Grooving (making a grove) / recessing (making a recess) / necking, Axial drilling and reaming (drill bit and reamer fitted in the tailstock) Centering (making a hole at the faced end of a cylinder so that the tailstock can hold it.