TURNING MACHINES
- 1. UNIT 2 TURNING MACHINES Centre lathe, constructional features, specification, operations – taper turning methods, thread cutting methods, special attachments, machining time and power estimation. Capstan and turret lathes- tool layout – automatic lathes: semi-automatic – single spindle: Swiss type, automatic screw type – multi spindle:
- 2. CENTRE LATHE
- 3. The following are the principle parts of the lathe Bed Head stock Tail stock Carriage Feed mechanism
- 4. BED Bed is the base of machines. It carries a headstock on its left end and tailstock on its right end. The carriage is mounted at the middle of bed.
- 5. Head stock The headstock assembly is permanently fastened to the left end of the bed. It carries a hollow spindle so that bars can be passed through it when it is required. There are two types of headstock driving mechanisms as follows Back geared headstock All geared head stock
- 6. Back gear arrangement is used for reducing the spindle speed which is necessary for thread cutting and knurling. Back geared headstock
- 7. All geared head stock All geared headstock is commonly used in modern lathes because of the following advantages It gives wider range of spindle speeds. It is more efficient and compact. The vibration of spindle is reduced. Belt shifting is eliminated. More power can be transmitted.
- 9. Tail stock Tailstock is situated at the right end of the bed. It is used for supporting the right end of the work piece.
- 10. Carriage The carriage is a moving part that slides over the guide ways between headstock and tailstock. It carries the following parts. Saddle Cross slide Compound rest Tool post Single screw tool post Open side tool post Four bolt tool post Four way tool post
- 12. Feed mechanism Feed is defined as the movement of the tool relative to the work. There are three types of feed longitudinal, cross and angular feed.
- 13. The following feed mechanisms are used Tumbler gear reversing mechanism Quick change gearbox Tumbler gear quick change gearbox Apron mechanism
- 14. Tumbler gear reversing mechanism
- 16. Tumbler gear quick change gearbox
- 17. Apron mechanism
- 18. Specification of a lathe
- 19. Types of lathe Lathes are classified in many ways with respect to size, design, method of drive and purposes. Speed lathe Wood working lathe Metal spinning lathe Metal turning lathe Polishing lathe Engine lathe Step cone pulley drive lathe Geared lathe Variable speed lathe Bench lathe Tool room lathe Semi automatic lathe Capstan lathe Turret lathe Automatic lathe Special purpose lathe Copying lathe
- 21. TAPER TURNING METHODS Form tool method Tailstock set over method Compound rest method Taper turning attachment method
- 22. Form tool method It is one of the simplest methods to produce short taper. Taper length should be less than the tool cutting edge length.
- 24. Tailstock set over method
- 27. Taper turning attachment method
- 28. THREAD CUTTING METHODS Thread cutting is done in different methods Reversing the machine Marketing the lathe parts Using a chasing dial or thread indicator Using thread chaser
- 29. Using a chasing dial or thread indicator
- 30. SPECIAL ATTACHMENTS Generally milling and grinding are performed on lathes by using special attachments Milling attachments Milling is the process of removing metal by moving the work against a rotating cutter. this operation is carried out in two methods depending upon the form of profiles. For cutting grooves or keyways For cutting multiple grooves and gear wheel
- 31. Grinding attachment Grinding is the operation of removing metal in fine form of chips. It is done by moving the work against a rotating abrasive wheel. This abrasive wheel is known as grinding wheel.
- 32. WORK HOLDING DEVICES Some of the standard work holding devices used to hold the work in a lathe are given below. Chucks Centres Face plate Angle plate Mandrels Steady and follower rest
- 33. Chucks Three jaw chuck or self centering chuck Four jaw chuck or independent chuck Magnetic chuck
- 34. Three jaw chuck or self centering chuck
- 35. Four jaw chuck or independent chuck
- 36. Magnetic chuck
- 37. Centres
- 38. Face plate
- 39. Angle plate
- 41. Steady and follower rest
- 42. AUTOMATIC LATHES AND SEMI AUTOMATIC LATHES In an ordinary centre lathe, changing and setting of tools consume more time. It reduces the rate of production and increases the cost of production. The changes of centre lathe into some special lathes is called semi automatic lathes and automatic lathes. The turret lathes are used in heavy jobs whereas the capstan lathe is used for light and small jobs.
- 43. Capstan and Turret lathe
- 44. THE MAIN PARTS OF CAPSTAN AND TURRET LATHES Bed Cross slide Head stock Turret head and saddle
- 45. BED Bed is the base part of the lathe. It is box type which is made of cast iron. The bed should be strong and rigid to withstand heavy loads, force and vibrations during machining.
- 46. CROSS SLIDE The two types of cross slides are as follows Reach over type It is mounted on bed guide ways in between head stock and turret. The cross slide has two tool posts. The tool post can move both in perpendicular and parallel direction to the spindle axis. In the rear tool post, the parting off tool is clamped in an inverted position to make the direction of work piece anti clock wise with respect to tool movement. Side hung type This type of cross slide is entirely supported on the front way which has no rear tool post. It provides a greater swing capacity to accommodate large diameter work piece. It is mainly used in turret lathe.
- 47. HEAD STOCK Headstock of capstan and turret lathe is similar to a head in ordinary centre lathes but heavier in construction. The four main types of head stock are as follows Step cone pulley driven head stock Direct electric motor driven head stock All geared head stock Pre-selective stock
- 48. SADDLE
- 50. In a capstan lathe, the turret head is mounted on a ram which slides on the saddle. It can be positioned on lathe bed ways and clamped well. In a turret lathe, the turret head is mounted on the saddle itself which slides on the bed ways during machining. It is mainly used in turret lathes.
- 51. TURRET HEAD A turret head has a hexagonal block having six faces with a bore for mounting six or more than six tools at a time. Turret head is mounted on the ram fitted with turret slides longitudinally on a saddle. Each tool is indexed through 60° by the rotation of a circular plate. The circular plate is automatically indexed along with the turret head. Bringing the next tool into the cutting position is known as Geneva mechanism.
- 52. GENEVA MECHANISM (OR) INDEXING MECHANISM The turret is provided with automatic indexing mechanism. To index the turret by 1/6 of a revolution, the ram is returned to the starting position. Then, the next tool comes into position to perform the machining operation.
- 54. WORKING PRINCIPLE OF CAPSTAN AND TURRET LATHES Drilling, boring, reaming, counter boring, turning and threading tools are mounted on the hexagonal turret head. Forming, chamfering, knurling and necking tools are mounted at the front end of the square turret. Parting off tool is mounted on the rear end of the square turret in an inverted or in a reversed position.
- 55. SPECIFICATION OF CAPSTAN AND TURRET LATHES Number of spindle speeds Number of feeds for the carriage Number of feeds for the turret Net weight of the machine Floor space required Power of the motor required
- 56. ADVANTAGES OF CAPSTAN AND TURRET LATHES The production rate is high Heavier and larger work piece chucking can be done It has wider range of speeds Larger number of tools can be held More than one operation can be performed at the same time It is more rigid. Hence, its withstands heavy cuts Semi skilled operators are enough Labour cost is less
- 57. Sl No. CAPSTAN LATHE TURRET LATHE 1 Turret head is mounted on a ram which slides over the saddle Turret head is directly mounted on saddle. But it slides on the bed 2 The turret movement is limited The turret moves on the entire length of the bed without any restrictions 3 Hence, shorter workpiece can be machined Longer workpiece can be machined 4 It does not provide rigidity It provide rigidity and strong 5 It is very much useful for light duty application It is useful for heavy duty application 6 Turret head moved manually Turret head cannot moved manually 7 The maximum size of 60 mm diameter work can be accommodated It can accommodate only 125 mm to 220mm
- 58. WORK HOLDING DEVICES The work holding devices used on capstan and turret lathes are mostly automatic types. It reduces the setting time. Collets Draw back collet Push out collet Dead length collet Chucks Fixture
- 59. COLLETS
- 60. Draw back collet
- 61. Push out collet
- 63. Chucks
- 64. Fixture A specially designed member to locate and grip a work piece is called as fixture. It is mounted on the spindle by replacing a chuck or collet.
- 66. TOOL HOLDING DEVICES To hold these tools in the respective positions, the various types of tool holders are fitted in a hexagonal turret or front tool post of the square turret or in the rear tool post. The following are the various types of tool holders Straight cutter tool holder Adjustable angle cutter tool holder Multiple cutter holder Offset cutter holder Sliding tool holder Knee tool holder Flange tool holder Roller steady box tool holder Self opening type die holder Knurling tool holder Collapsible taps Combination tool holder
- 67. Straight cutter tool holder
- 68. Adjustable angle cutter tool holder
- 72. Knee tool holder
- 74. Roller steady box tool holder
- 76. Self opening type die holder
- 78. Collapsible taps
- 79. TOOL LAYOUTS Turret and capstan lathe are mainly used for machining workpieces in rapid speed. Before starting the production, the following works are carried out. Selection of tools Designing of special tools Selection of speeds Selection of feeds Setting the required length of work piece.
- 80. Tool layouts mainly consist of three stages Planning and scheduling stage Detailed sketching of various stages Sketching the plan showing the various tools
- 81. AUTOMATIC LATHES In automatic lathes, all operations required to finish off the work piece are automatically done without the attention of an operator. These machines are meant for producing identical parts without participation of an operator. All operations including loading and unloading are automatically done. By using the control system, all working and idle operations are performed in a definite sequence.
- 82. ADVANTAGES OF AUTOMATIC LATHES Mass production of identical parts is highly achieved High accuracy is maintained Time of production is minimized Less floor space is required Unskilled labour is enough It minimizes the labour cost One operator can be utilized to operate more than one machine.
- 83. Classification of automatic lathes Classification according to the type of work material used Bar stock machine Chucking machine Classification according to the number of spindles Single spindle automats Multi spindle automats Classification according to the arrangements of spindles Horizontal spindle type Vertical spindle type Classification according to the feed control Single cam shaft rotating at constant speed Single cam shaft with two speeds Two cam shaft Classification according to the use Single purpose machine General purpose machine
- 84. SINGLE SPINDLE AUTOMATIC LATHES
- 85. The following types of single spindle automatic lathe are mostly used Automatic cutting off machine Automatic screw cutting machine Swiss type automatic screw machine
- 86. Automatic cutting off machine
- 88. Automatic screw cutting machine
- 90. Swiss type automatic screw machine
- 91. It consists of four major parts The sliding headstock through which the bar stock is passed and gripped by a carbide lined guide bush The camshaft which controls the bar stock and cutting tool movements The tool bracket which supports five tool slides and a bush for stock Auxiliary attachments for performing various operations such as knurling, drilling, tapping, screwing, slotting, recessing etc.
- 92. Working principle The bar stock is held in the rotating spindle by a collet check. head stock slides along the bed ways with the rotating bar stock. This headstock movement gives a longitudinal feed to the work. All tools in the tool slides remove materials from the work piece at the same time. The tool in the feed base attachment may also do operations such as drilling.
- 93. Advantages of Swiss type screw machine It is used to manufacture precision turning of small parts It has five tool slides Wide range of speeds is available It is rigid in construction Tolerance of 0.005 to 0.0125mm is obtained
- 94. Multi spindle automatic lathes Multiple spindle automatic lathes are machines which can produce larger work pieces than single spindle automats. The principle advantage of the multi spindle automat is that it has a tool slide working simultaneously on the jobs on all spindles and hence, the time for producing a piece is the time for the longest cut
- 96. Classification of multi spindle automatic lathes According to the type of work piece used Bar type machine Chucking type machine According to the arrangement of spindle Horizontal spindle type Vertical spindle type According to the principle of operation Parallel action type Progressive action type
- 97. Parallel action Multiple spindle automatic machine
- 98. Progressive action Multiple spindle automatic machine
- 99. Sl No. Parallel action machine Progressive action machine 1 Same operation is done on all jobs in all spindles Different operations are done on jobs at each station one after another 2 The rate of production is very high The rate of production is moderate 3 If anything goes wrong in one station, the production in that particular station only is affected If anything goes wrong in one station, the production is completely affected in all station. 4 Small parts of simple shapes are produced Parts of complicated shapes can be produced
- 100. Sl No. Single spindle Multi spindle 1 There is only one spindle There are 2,4,5,6 or 8 spindle 2 Only one work piece is machined at a time A number of work pieces are machined at a time 3 The rate of production is low The rate of production is high 4 Machining accuracy is higher Machining accuracy is lower 5 Tool setting time and tooling cost is less Tool setting time and tooling cost is more