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The Lathe.

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Presentation on theme: "The Lathe."— Presentation transcript:

1 The Lathe

2 History Lathe forerunner of all machine tools
First application was potter's wheel Rotated clay and enabled it to be formed into cylindrical shape Very versatile (many attachments) Used for turning, tapering, form turning, screw cutting, facing, drilling, boring, spinning, grinding and polishing operations Cutting tool fed either parallel or right angles 2

3 Special Types of Lathes
Engine lathe Not production lathe, found in school shops, toolrooms, and jobbing shops Basic to all lathes Turret lathe Used when many duplicate parts required Equipped with multisided toolpost (turret) to which several different cutting tools mounted Employed in given sequence 3

4 Engine Lathe Parts

5 Engine Lathe Accurate and versatile machine Operations Three common
Turning, tapering, form turning, threading, facing, drilling, boring, grinding, and polishing Three common Toolroom Heavy-duty Gap-bed 5

6 Lathe Size and Capacity
Designated by largest work diameter that can be swung over lathe ways and generally the maximum distance between centers Manufactured in wide range of sizes Most common: 9- to 30- in. swing with capacity of 16 in. to 12 feet between centers Typical lathe: 13 in. swing, 6 ft long bed, 36 in. Average metric lathe: mm swing and bed length of 500 – 3000 mm 6

7 Indicated by the swing and the length of the bed
Lathe Size Indicated by the swing and the length of the bed

8 Parts of the Lathe Headstock Tailstock Quick Bed Change Gearbox
Carriage 8

9

10

11 Setting Speeds on a Lathe
Speeds measured in revolutions per minute Changed by stepped pulleys or gear levers Belt-driven lathe Various speeds obtained by changing flat belt and back gear drive Geared-head lathe Speeds changed by moving speed levers into proper positions according to r/min chart fastened to headstock Safety Note!! NEVER change speeds when lathe is running. 11

12 Shear Pins and Slip Clutches
Prevents damage to feed mechanism from overload or sudden torque Shear pins Made of brass Found on feed rod, lead screw, and end gear train Spring-loaded slip clutches Found only on feed rods When feed mechanism overloaded, shear pin will break or slip clutch will slip causing feed to stop 12

13 Shear pin in end gear train prevents damage to the gears in case of an overload
Spring-ball clutch will slip when too much strain is applied to feed rod

14 Lathe Accessories

15 Lathe Accessories Divided into two categories
46-15 Lathe Accessories Divided into two categories Work-holding, -supporting, and –driving devices Lathe centers, chucks, faceplates Mandrels, steady and follower rests Lathe dogs, drive plates Cutting-tool-holding devices Straight and offset toolholders Threading toolholders, boring bars Turret-type toolposts 15

16 46-16 Lathe Centers Work to be turned between centers must have center hole drilled in each end Provides bearing surface Support during cutting Most common have solid Morse taper shank 60º centers, steel with carbide tips Care to adjust and lubricate occasionally 16

17 Chucks Used extensively for holding work for machining operations
46-17 Chucks Used extensively for holding work for machining operations Work large or unusual shape Most commonly used lathe chucks Three-jaw universal Four-jaw independent Collet chuck 17

18 Three-jaw Universal Chuck
46-18 Three-jaw Universal Chuck Holds round and hexagonal work Grasps work quickly and accurate within few thousandths/inch Three jaws move simultaneously when adjusted by chuck wrench Caused by scroll plate into which all three jaws fit Two sets of jaw: outside chucking and inside chucking 18

19 Four-Jaw Independent Chuck
46-19 Four-Jaw Independent Chuck Used to hold round, square, hexagonal, and irregularly shaped workpieces Has four jaws Each can be adjusted independently by chuck wrench Jaws can be reversed to hold work by inside diameter 19

20 46-20 Headstock Spindles Universal and independent chuck fitted to three types of headstock spindles Threaded spindle nose Screws on in a clockwise direction Tapered spindle nose Held by lock nut that tightens on chuck 20

21 Cam-lock mating stud on chuck or faceplate
46-21 Headstock Spindles Cam-lock spindle nose Held by tightening cam-locks using T-wrench Chuck aligned by taper on spindle nose Registration lines on spindle nose Registration lines on cam-lock Cam-locks Cam-lock mating stud on chuck or faceplate 21

22 Collet Chuck Most accurate chuck Used for high-precision work
46-22 Collet Chuck Most accurate chuck Used for high-precision work Spring collets available to hold round, square, or hexagon-shaped workpieces Each collet has range of only few thousandths of an inch over or under size stamped on collet 22

23 46-23 Collet Chuck | Special adapter fitted into taper of headstock spindle, and hollow draw bar having internal thread inserted in opposite end of headstock spindle. It draws collet into tapered adapter causing collet to tighten on workpiece.

24 Types of Lathe Dogs Standard bent-tail lathe dog
46-24 Types of Lathe Dogs Standard bent-tail lathe dog Most commonly used for round workpieces Available with square-head setscrews of headless setscrews Straight-tail lathe dog Driven by stud in driveplate Used in precision turning 24

25 Types of Lathe Dogs Safety clamp lathe dog Clamp lathe dog
46-25 Types of Lathe Dogs Safety clamp lathe dog Used to hold variety of work Wide range of adjustment Clamp lathe dog Wider range than others Used on all shapes 25

26 Left-Hand Offset Toolholder
46-26 Left-Hand Offset Toolholder Offset to the right Designed for machining work close to chuck or faceplate and cutting right to left Designated by letter L 26

27 Right-Hand Offset Toolholder
46-27 Right-Hand Offset Toolholder Offset to the left Designed for machining work close to the tailstock and cutting left to right Also for facing operations Designated by letter R 27

28 Straight Toolholder General-purpose type
46-28 Straight Toolholder General-purpose type Used for taking cuts in either direction and for general machining operations Designated by letter S 28

29 Toolholders for Indexable Carbide Inserts
46-29 Toolholders for Indexable Carbide Inserts Held in holder by cam action or clamps Types available Conventional Turret-type Heavy-duty toolposts 29

30 Cutting-Off (Parting) Tools
46-30 Cutting-Off (Parting) Tools Used when work must be grooved or parted off Long, thin cutting-off blade locked securely in toolholder by either cam lock or locking nut Three types of parting toolholders Left-hand Right-hand Straight 30

31 46-31 Threading Toolholder Designed to hold special form-relieved thread-cutting tool Has accurately ground 60º angle Maintained throughout life of tool Only top of cutting surface sharpened when becomes dull 31

32 Super Quick-Change Toolpost
46-32 Super Quick-Change Toolpost

33 Cutting Speed, Feed, and Depth of Cut

34 47-34 Cutting Speed Rate at which point on work circumference travels past cutting tool Always expressed in feet per minute (ft/min) or meters per minute (m/min) Important to use correct speed for material Too high: cutting-tool breaks down rapidly Too low: time lost, low production rates 34

35 47-35 Lathe Cutting Speeds in Feet and Meters per Minute Using High-Speed Steel Toolbit Turning and Boring Rough Cut Finish Cut Threading Material ft/min m/min ft/min m/min ft/min m/min Machine steel Tool steel Cast iron Bronze Aluminum 35

36 Calculating Lathe Spindle Speed
47-36 Calculating Lathe Spindle Speed Given in revolutions per minute Cutting speed of metal and diameter of work must be known Proper spindle speed set by dividing CS (in/min) by circumference of work (in) 36

37 47-37 Example: Calculate r/min required to rough-turn 2 in. diameter piece of machine steel (CS 90): Metric Formula 37

38 47-38 Lathe Feed Distance cutting tool advances along length of work for every revolution of the spindle Feed of engine lathe dependent on speed of lead screw for feed rod Speed controlled by change gears in quick-change gearbox 38

39 Two Cuts Used to Bring Diameter to Size
47-39 Two Cuts Used to Bring Diameter to Size Roughing cut Purpose to remove excess material quickly Coarse feed: surface finish not too important .010- to .015-in. (0.25- to 0.4-mm) Finishing cut Used to bring diameter to size Fine feed: Produce good finish .003- to .005-in (0.07- to mm) 39

40 Feeds for Various Materials (using high-speed steel cutting tool)
47-40 Feeds for Various Materials (using high-speed steel cutting tool) Rough Cuts Finish Cuts Material in mm in mm Machine steel .010– – – –0.25 Tool steel .010– – – –0.25 Cast iron .015– – – –0.3 Bronze .015– – – –0.25 Aluminum .015– – – –0.25

41 47-41 Depth of Cut Depth of chip taken by cutting tool and one-half total amount removed from workpiece in one cut Only one roughing and one finishing cut Roughing cut should be deep as possible to reduce diameter to within .030 to .040 in. (0.76 to 1 mm) of size required Finishing cut should not be less than .005 in. 41

42 Example: Depth of cut on a lathe
47-42 Example: Depth of cut on a lathe

43 Factors Determining Depth of Rough-Turning Cut
47-43 Factors Determining Depth of Rough-Turning Cut Condition of machine Type and shape of cutting tool used Rigidity of workpiece, machine, and cutting tool Rate of feed 43

44 47-44 Inch System Circumference of crossfeed and compound rest screw collars divided into equal divisions Each has value of .001 in. Turn crossfeed screw clockwise 10 graduations, cutting tool moved .010 in. toward work Lathe revolves, so .010 depth of cut taken from entire work circumference reducing diameter .020 in. Check machine for its' graduations 44

45 47-45 On machines where the workpiece revolves, the cutting tool should be set in for only half the amount to be removed from the diameter.

46 47-46 On machines where the workpiece does not revolve, the cutting tool should be set in for the amount of material to be removed.

47 Hints on Graduated Collar Use
47-47 Hints on Graduated Collar Use Make sure collar is secure before setting a depth of cut All depths of cut must be made by feeding cutting tool toward workpiece If graduated collar turned past desired setting, must be turned backward half-turn and fed into proper setting to remove backlash Never hold graduated collar when setting depth of cut 47

48 47-48 Graduated collar on compound rest can be used for accurately setting depth of cut Shoulder turning Compound rest set at 90º to cross-slide Lock carriage in place Spacing of shoulders to within .001 in. accuracy Facing Compound rest swung to 30º, amount removed from length of work = ½ amount of feed on collar Machining accurate diameters Set compound rest to 84º16' to the cross-slide .001 in movement = in. infeed movement 48

49 The compound rest is set at 84º16' for making fine settings.
47-49 The compound rest is set at 84º16' for making fine settings.

50 Lathe Safety

51 Safety Be aware of safety requirements in any area of shop
48-51 Safety Be aware of safety requirements in any area of shop Always attempt to observe safety rules Failure results in: Serious injury Resultant loss of time and pay Loss of production to company 51

52 Safety Precautions Lathe hazardous if not operated properly
48-52 Safety Precautions Lathe hazardous if not operated properly Important to keep machine and surrounding area clean and tidy Accidents usually caused by carelessness 52

53 Safety Precautions Always wear approved safety glasses
48-53 Safety Precautions Always wear approved safety glasses Rollup sleeves, remove tie and tuck in loose clothing Never wear ring or watch 53

54 Safety Precautions Do not operate lathe until understand controls
48-54 Safety Precautions Do not operate lathe until understand controls Never operate machine if safety guards removed Stop lathe before measure work or clean, oil or adjust machine Do not use rag to clean work or machine when in operation Rag can get caught and drag in hand 54

55 48-55 Safety Precautions Never attempt to stop a lathe chuck or driveplate by hand Be sure chuck or faceplate mounted securely before starting If loose, becomes dangerous missile Always remove chuck wrench after use Fly out and injure someone Become jammed, damaging wrench or lathe 55

56 48-56 Safety Precautions Move carriage to farthest position of cut and revolve lathe spindle one turn by hand Ensure all parts clear without jamming Prevent accident and damage to lathe Keep floor around machine free from grease, oil, metal cuttings, tools and workpieces Oil and grease can cause falls Objects on floor become tripping hazards 56

57 Safety Precautions Avoid horseplay at all times
48-57 Safety Precautions Avoid horseplay at all times Always remove chips with brush Chips can cause cuts if use hands Chips become embedded if use cloths Always remove sharp toolbit from toolholder when polishing, filing, cleaning, or making adjustments 57

58 Mounting, Removing, and Aligning Lathe Centers
Unit 49

59 Objectives Mount and/or remove lathe centers properly
49-59 Objectives Mount and/or remove lathe centers properly Align lathe centers by visual, trial-cut, and dial-indicator methods

60 49-60 Lathe Centers Work machined between centers turned for some portion of length, then reversed, and other end finished Critical when machining work between centers that live center be absolutely true Concentric work 60

61 49-61 To Mount Lathe Centers Remove any burrs from lathe spindle, centers, or spindle sleeves Clean tapers on lathe centers and in headstock and tailstock spindles Partially insert cleaned center in lathe spindle Force center into spindle Follow same procedure when mounting tailstock center Check trueness of center 61

62 To Remove Lathe Centers
49-62 To Remove Lathe Centers Live center Use knockout bar pushed through headstock spindle (slight tap) Use cloth over center and hold to prevent damage Dead center Turn tailstock handwheel to draw spindle back into tailstock End of screw contacts end of dead center, forcing it out of spindle 62

63 Alignment of Lathe Centers
49-63 Alignment of Lathe Centers Parallel diameter produced when lathe center aligned Three common methods used to align Aligning centerlines on back of tailstock with each other Only a visual check and not too accurate 63

64 Alignment of Lathe Centers
49-64 Alignment of Lathe Centers Using the trial-cut method where small cut taken from each end of work and diameters measured with a micrometer Using parallel test bar and dial indicator Fastest and most accurate method 64

65 To Align Centers by Adjusting the Tailstock
49-65 To Align Centers by Adjusting the Tailstock Loosen tailstock clamp nut or level Loosen on of the adjusting screws, depending on direction tailstock must be moved and tighten other until line on top aligns with line on bottom half Tighten screw to lock both halves in place Make sure tailstock lines still aligned Lock tailstock clamp nut or lever 65

66 To Align Centers by Trial-Cut Method
49-66 To Align Centers by Trial-Cut Method Take a light cut (~.005 in.) to true diameter from section A at tailstock end for .250 in. long Stop feed and note reading on graduated collar of crossfeed handle Move cutting tool away from work with crossfeed handle Bring cutting tool close to headstock end 66

67 To Align Centers by Trial-Cut Method
49-67 To Align Centers by Trial-Cut Method Return cutting tool to same graduated collar setting as at section A Cut a .500-in (13 mm) length at section B and stop lathe Measure both diameters with micrometer 67

68 To Align Centers by Trial-Cut Method
49-68 To Align Centers by Trial-Cut Method If both diameters not same size, adjust tailstock either toward or away from cutting tool ½ difference of two readings Take another light cut at A and B at same crossfeed graduated collar setting. Measure diameters and adjust tailstock. 68

69 To Align Centers Using Dial Indicator and Test Bar
49-69 To Align Centers Using Dial Indicator and Test Bar Clean lathe and work center, mount test bar Adjust test bar snugly between centers and tighten tailstock spindle clamp Mount dial indicator on toolpost or lathe carriage Indicator plunger should be parallel to lathe bed and contact point set on center 69

70 To Align Centers Using Dial Indicator and Test Bar
49-70 To Align Centers Using Dial Indicator and Test Bar Adjust cross-slide Indicator registers approximately .025 in at tailstock, indicator bezel to 0 Move carriage by hand so indicator registers on diameter at headstock end and not indicator reading If both indicator readings not same, adjust tailstock with adjusting screws until indicator registers same at both ends 70

71 To Align Centers Using Dial Indicator and Test Bar
49-71 To Align Centers Using Dial Indicator and Test Bar Tighten adjusting screw that was loosened Tighten tailstock clamp nut Adjust tailstock spindle until test bar snug between lathe centers Recheck indicator readings at both ends and adjust tailstock, if necessary 71

72 Grinding Lathe Cutting Tools

73 Grinding Lathe Cutting Tool
50-73 Grinding Lathe Cutting Tool Wide variety of cutting tools for lathe All have certain angles and clearances regardless of shape Shape and Dimensions of General-purpose Lathe Toolbit 73

74 To Grind a General-Purpose Toolbit
50-74 To Grind a General-Purpose Toolbit Dress face of grinding wheel Grip toolbit firmly, supporting hands on grinder toolrest Hold toolbit at proper angel to grind cutting edge angle Tilt bottom of toolbit toward wheel and grind 10º side relief or clearance angle 74

75 Cutting edge ~ ½ In long and extend over ¼ width of toolbit
50-75 Cutting edge ~ ½ In long and extend over ¼ width of toolbit 10º side relief or clearance angle

76 While grinding, move toolbit back and forth across face of wheel
50-76 While grinding, move toolbit back and forth across face of wheel Prevents grooving wheel Toolbit must be cooled frequently during grinding Never overheat toolbit! Never quench stellite or cemented-carbide tools Never grind carbides with aluminum oxide wheel 76

77 50-77 Grind end cutting edge so it forms angle of a little less than 90º with side cutting edge Hold tool so that end cutting edge angle and end relief angle of 15º ground at same time 70º to 80º Point Angle 77

78 50-78 Using toolbit grinding gage, check amount of end relief when toolbit is in toolholder 78

79 Side rake ground the length of the cutting edge
50-79 Hold top of toolbit approximately 45º to axis of wheel and grind side rake to approximately 14º Do not grind below top of toolbit Creates a chip trap Side rake ground the length of the cutting edge 79

80 With oilstone, hone cutting edge of toolbit slightly
50-80 Grind slight radius on point of cutting tool, being sure to maintain same front and side clearance angle With oilstone, hone cutting edge of toolbit slightly Lengthen life of toolbit Enable it to produce better surface finish on workpiece 80

81 Machining Between Centers

82 Machining Between Centers
52-82 Machining Between Centers Training programs (schools) Remove and replace work in lathe many times before completed Need assurance that machined diameter will run true with other diameters Machining between centers saves time in setting up Common operations Facing, rough and finish-turning, shoulder turning, filing and polishing 82

83 Setting Up a Cutting Tool
52-83 Setting Up a Cutting Tool Move toolpost to the left-hand side of the T-slot in the compound rest Mount tool- holder in toolpost so setscrew in toolholder 1 in. beyond toolpost 83

84 Heavy Cuts: Set toolholder at right angles to work
52-84 Heavy Cuts: Set toolholder at right angles to work 84

85 Setting Up a Cutting Tool: cont.
52-85 Setting Up a Cutting Tool: cont. Insert proper cutting tool into toolholder, having tool extend .500 in. beyond toolholder and never more than twice its thickness Set cutting-tool point to center height Check it against lathe center point Tighten toolpost securely to prevent it from moving during a cut 85

86 Purposes of a Trial Cut Produce accurate turned diameter
52-86 Purposes of a Trial Cut Produce accurate turned diameter Measured with micrometer Set cutting-tool point to the diameter Set crossfeed micrometer collar to the diameter 86

87 Procedure to Take a Trial Cut
52-87 Procedure to Take a Trial Cut Set up workpiece and cutting tool as for turning Set proper speeds and feed to suit material Start lathe and position toolbit over work approximately .125 in. from end Turn compound rest handle clockwise ¼ of a turn to remove any backlash 87

88 Do NOT move crossfeed handle setting
52-88 feed toolbit into work by turning crossfeed handle clockwise until light ring appears around entire circumference of work Do NOT move crossfeed handle setting Turn carriage handwheel until toolbit clears end of workpiece by about .060 in. Turn crossfeed handle clockwise about .010 in. and take trial cut .250 in. along length of work Disengage automatic feed and clear toolbit past end of work with carriage handwheel 88

89 Turn crossfeed handle clockwise ½ amount of material to be removed
52-89 Stop the lathe Test accuracy of micrometer by cleaning and closing measuring faces and then measure trial-cut diameter Calculate how much material must still be removed from diameter of work Turn crossfeed handle clockwise ½ amount of material to be removed 89

90 Take another trial cut .250 in. long and stop the lathe
52-90 Take another trial cut .250 in. long and stop the lathe Clear toolbit over end of work with carriage handwheel Measure diameter and readjust crossfeed handle until diameter is correct Machine diameter to length 90

91 52-91 Rough Turning Removes as much metal as possible in shortest length of time Accuracy and surface finish are not important in this operation .020- to .030-in. feed recommended Work rough-turned to Within .030 in. of finished size when removing up to .500 in. diameter Within .060 in. when removing > .500 in. 91

92 Procedure for Rough Turning
52-92 Procedure for Rough Turning Set lathe to correct speed for type and size of material being cut Adjust quick-change gearbox for a to .030-in. feed Depends on depth of cut and condition of machine Move toolholder to left-hand side of compound rest and set toolbit height to center 92

93 Take light trial cut at right-hand end of work for a .250 in. length
52-93 Tighten toolpost securely to prevent toolholder from moving during machining Take light trial cut at right-hand end of work for a .250 in. length Measure work and adjust toolbit for proper depth of cut Cut along for .250 in., stop lathe, and check diameter for size Diameter .030 in. over finish size Readjust depth of cut, if necessary 93

94 Finish Turning Follows rough turning
52-94 Finish Turning Follows rough turning Produces smooth surface finish and cuts work to an accurate size Factors affecting type of surface finish Condition of cutting tool Rigidity of machine and work Lathe speeds and feeds 94

95 Procedure For Finish Turning
52-95 Procedure For Finish Turning Make sure cutting edge of toolbit free from nicks, burrs, etc. Set toolbit on center; check it against lathe center point Set lathe to recommended speed and feed 95

96 Take light trial cut .250 in. long at right-hand end of work
52-96 Take light trial cut .250 in. long at right-hand end of work Produce true diameter Set cutting tool to diameter Set graduated collar to diameter Stop lathe and measure diameter Set depth of cut for half amount of material to be removed Cut along for .250 in., stop lathe, check Readjust depth of cut and finish-turn 96

97 52-97 Filing in a Lathe Only to remove small amount of stock, remove burrs, or round off sharp corners Work should be turned to within .002 to .003 in. of size For safety, file with left hand so arms and hands kept clear of revolving chuck Remove toolbit from toolholder before filing Cover lathe bed with paper before filing 97

98 Procedure to File in a Lathe
52-98 Procedure to File in a Lathe Set spindle speed to twice that for turning Mount work between centers, lubricate, and carefully adjust dead center in work Move carriage as far to right as possible and remove toolpost Disengage lead screw and feed rod Select 10- or 12-in. mill file or long-angle lathe file 98

99 52-99 Start lathe Grasp file handle in left hand and support file point with fingers of right hand 99

100 52-100 Apply light pressure and push file forward to its full length; release pressure on return stroke Move file about half width of file for each stroke and continue filing until finished Use strokes per minute Safety precautions Roll sleeves above elbow Remove watches and rings Never use file without properly fitted handle Never apply too much pressure Clean file frequently with file brush 100

101 Procedure for Polishing in a Lathe
52-101 Procedure for Polishing in a Lathe Select correct type and grade of abrasive cloth for finish desired Piece about 6 – 8 in. long and 1 in. wide Use aluminum oxide abrasive cloth for ferrous metals Use silicon carbide abrasive cloth should be used for nonferrous metals Set lathe to run at high speed Disengage feed rod and lead screw 101

102 Remove toolpost and toolholder Lubricate and adjust dead center
52-102 Remove toolpost and toolholder Lubricate and adjust dead center Roll sleeves up above elbows and tuck in any loose clothing Start lathe Hold abrasive cloth on work With right hand, press cloth firmly on work while tightly holding other end of abrasive cloth with left hand Move cloth slowly back and forth 102

103 52-103 Shoulder Shoulder: the change in diameters, or step, when turning more than one diameter on a piece of work Three common types of shoulders Square Filleted Angular or Tapered 103

104 Three Types of Shoulders
52-104 Three Types of Shoulders

105 Knurling, Grooving, and Form Turning

106 53-106 Knurling Process if impressing a diamond-shaped or straight-line patter into the surface of the workpiece Improve its appearance Provide better gripping surface Increase workpiece diameter when press fit required 106

107 Knurling Diamond- and straight-pattern rolls available in three styles
53-107 Knurling Diamond- and straight-pattern rolls available in three styles Fine Medium Course 107

108 53-108 Knurling Tool Toolpost-type toolholder on which pair of hardened-steel rolls mounted Knurling tool with one set of rolls in self-centering head Knurling tool with three sets of rolls in revolving head 108

109 Universal Knurling Tool System
53-109 Universal Knurling Tool System Dovetailed shank and as many as seven interchangeable knurling heads that can produce wide range of knurling patterns Combines in one tool Versatility Rigidity Ease of handling Simplicity 109

110 Procedure to Knurl in a Lathe
53-110 Procedure to Knurl in a Lathe Mount work between centers and mark required length to be knurled If work held in chuck for knurling, right end of work should be supported with revolving tailstock center Set lathe to run at one-quarter speed required for turning Set carriage feed to .015 to .030 in. 110

111 Set knurling tool at right angles to workpiece and tighten it securely
53-111 Set center of floating head of knurling tool even with dead-center point Set knurling tool at right angles to workpiece and tighten it securely 111

112 Start machine and lightly touch rolls against work to check tracking
53-112 Start machine and lightly touch rolls against work to check tracking Move knurling tool to end of work so only half the roll face bears against work Force knurling tool into work approximately .025 in. and start lathe OR Start lathe and then force knurling tool into work until diamond pattern come to point 112

113 Stop lathe and examine pattern
53-113 Stop lathe and examine pattern Once pattern correct, engage automatic carriage feed and apply cutting fluid to knurling rolls Knurl to proper length and depth Do not disengage feed until full length has been knurled; otherwise, rings will be formed on knurled pattern If knurling pattern not to point after length has been knurled, reverse lathe feed and take another pass across work 113

114 53-114 Grooving Square Round V-shaped Done at end of thread to permit full travel of nut up to a shoulder or at edge of shoulder for proper fit Also called recessing, undercutting, or necking Rounded grooves used where there is strain on part 114

115 Procedure to Cut a Groove
53-115 Procedure to Cut a Groove Grind toolbit to desired size and shape of groove required Lay out location of groove Set lathe to half the speed for turning Mount workpiece in lathe Set toolbit to center height 115

116 Locate toolbit on work at position where groove is to be cut
53-116 Locate toolbit on work at position where groove is to be cut Start lathe and feed cutting tool toward work using crossfeed handle until toolbit marks work lightly Hold crossfeed handle in position and set graduated collar to zero Calculate how far crossfeed screw must be turned to cut groove to proper depth Feed toolbit into work slowly using crossfeed handle 116

117 Apply cutting fluid to point of cutting tool
53-117 Apply cutting fluid to point of cutting tool To ensure cutting tool will not bind in groove, move carriage slightly to left and to right while grooving Should chatter develop, reduce spindle speed Stop lathe and check depth of groove with outside calipers or knife-edge verniers 117

118 Threads and Thread Cutting

119 55-119 Threads Used for hundreds of years for holding parts together, making adjustments, and transmitting power and motion Art of producing threads continually improved Massed-produced by taps, dies, thread rolling, thread milling, and grinding 119

120 Threads Thread Used for several purposes:
55-120 Threads Thread Helical ridge of uniform section formed on inside or outside of cylinder or cone Used for several purposes: Fasten devices such as screws, bolts, studs, and nuts Provide accurate measurement, as in micrometer Transmit motion Increase force 120

121 55-121 Thread Terminology Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

122 Thread Terminology Screw thread External thread Internal thread
55-122 Thread Terminology Screw thread Helical ridge of uniform section formed on inside or outside of cylinder or cone External thread Cut on external surface or cone Internal thread Produced on inside of cylinder or cone 122

123 Major diameter Minor diameter Pitch diameter
55-123 Major diameter Largest diameter of external or internal thread Minor diameter Smallest diameter of external or internal thread Pitch diameter Diameter of imaginary cylinder that passes through thread at point where groove and thread widths are equal Equal to major diameter minus single depth of thread Tolerance and allowances given at pitch diameter line 123

124 Number of threads per inch
55-124 Number of threads per inch Number of crests or roots per inch of threaded section (Does not apply to metric threads) Pitch Distance from point on one thread to corresponding point on next thread, measured parallel to axis Expressed in millimeters for metric threads Lead Distance screw thread advances axially in one revolution (single-start thread, lead = pitch) 124

125 Root Crest Flank Bottom surface joining sides of two adjacent threads
55-125 Root Bottom surface joining sides of two adjacent threads External thread on minor diameter Internal thread on major diameter Crest Top surface joining two sides of thread External thread on major diameter Internal thread on minor diameter Flank Thread surface that connects crest with root 125

126 Depth of thread Angle of thread Helix angle
55-126 Depth of thread Distance between crest and root measured perpendicular to axis Angle of thread Included angle between sides of thread measured in axial plane Helix angle Angle that thread makes with plane perpendicular to thread axis 126

127 Right-hand thread Left-hand thread
55-127 Right-hand thread Helical ridge of uniform cross section onto which nut is threaded in clockwise direction When cut on lathe, toolbit advanced from right to left Left-hand thread Helical ridge of uniform cross section onto which nut is threaded in counterclockwise direction When cut on lathe, toolbit advanced from left to right Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 127

128 55-128 Thread Forms April, 1975 ISO came to an agreement covering standard metric thread profile Specifies sizes and pitches for various threads in new ISO Metric Thread Standard Has 25 thread sizes, range in diameter from 1.6 to 100 mm Identified by letter M, nominal diameter, and pitch M 5 X 0.8 128

129 American National Standard Thread
55-129 American National Standard Thread Divided into four main series, all having same shape and proportions National Coarse (NC) National Fine (NF) National Special (NS) National Pipe (NPT) Has 60º angle with root and crest truncated to 1/8th the pitch Used in fabrication, machine construction 129

130 American National Standard Thread
55-130 American National Standard Thread Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 130

131 55-131 Unified Thread Developed by U.S., Britain, and Canada for standardized thread system Combination of British Standard Whitworth and American National Standard Thread Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 131

132 55-132 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 132

133 American National Acme Thread
55-133 American National Acme Thread Replacing square thread in many cases Used for feed screws, jacks, and vises D = minimum .500P = maximum .500P F = .3707P C = .3707P (for maximum depth) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 133

134 Brown & Sharpe Worm Thread
55-134 Brown & Sharpe Worm Thread Used to mesh worm gears and transmit motion between two shafts at right angles to each other but not in same plane D = .6866P F = .335P C = .310P Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 134

135 55-135 Square Thread Being replaced by Acme thread because of difficulty in cutting it Often found on vises and jack screws D = .500P F = .500P C = .500P Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 135

136 International Metric thread
55-136 International Metric thread Standardized thread used in Europe D = P (maximum) = P (minimum) F = 0.125P R = P (maximum) = 0.054P (minimum) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 136

137 Thread Fits and Classifications
55-137 Thread Fits and Classifications Fit Relationship between two mating parts Determined by amount of clearance or interference when they are assembled Nominal size Designation used to identify size of part Actual size Measured size of thread or part Basic size: size from which tolerances are set 137

138 55-138 Allowance Permissible difference between largest external thread and smallest internal thread Difference produces tightest fit acceptable for any given classification The allowance for a 1 in.—8 UNC Class 2A and 2B fit is: Minimum pitch diameter of the internal thread (2B) = in. Maximum pitch diameter of the external thread (2A) = in. Allowance = .002 in. 138

139 Tolerance Variation permitted in part size
55-139 Tolerance Variation permitted in part size May be expressed as plus, minus, or both Total tolerance is sum of plus and minus tolerances In Unified and National systems, tolerance is plus on external threads and minus on internal threads The tolerance for a 1 in.—8 UNC Class 2A thread is: Maximum pitch diameter of the external thread (2A) = in. Minimum pitch diameter of the external thread (2A) = in. Tolerance = in. 139

140 Limits Maximum and minimum dimensions of part
55-140 Limits Maximum and minimum dimensions of part The limits for a 1 in.—8 UNC Class 2A thread are: Maximum pitch diameter of the external thread (2A) = in.. Minimum pitch diameter of the external thread (2A) = in. 140

141 Three Categories of Unified Thread Fits
55-141 Three Categories of Unified Thread Fits External threads classified as 1A, 2A, and 3A and internal threads as 1B, 2B, 3B Classes 1A and 1B Threads for work that must be assembled Loosest fit Classes 2A and 2B Used for most commercial fasteners Medium or free fit Classes 3A and 3B Used where more accurate fit and lead required No allowance provided 141

142 Thread Calculations: Example 1
55-142 Thread Calculations: Example 1 To cut a correct thread on a lathe, it is necessary first to make calculations so thread will have the proper dimensions. Calculate pitch, depth, minor diameter, and width of flat for a ¾—10 UNC thread. D = single depth of thread P = pitch 142

143 Thread Calculations: Example 2
55-143 Thread Calculations: Example 2 What are the pitch, depth, minor diameter, width of crest and width of root for an M 6.3 X 1 thread? P = pitch = 1 mm D = x 1 = 0.54 mm 143

144 Procedure to Set the Quick-Change Gearbox for Threading
55-144 Procedure to Set the Quick-Change Gearbox for Threading Check drawing for thread pitch required From chart on quick-change gearbox, find whole number that represents pitch in threads per inch or in millimeters With lathe stopped, engage tumbler lever in hole, which is in line with the pitch Set top lever in proper position as indicated on chart 144

145 Engage sliding gear in or out as required
55-145 Engage sliding gear in or out as required Turn lathe spindle by hand to ensure that lead screw revolves Recheck lever settings to avoid errors 145

146 55-146 Thread-Chasing dial Lathe spindle and lead screw must be in same relative position for each cut Thread-chasing dial attached to carriage for this purpose Dial has eight divisions Even threads use any division Odd threads either numbered or unnumbered: not both Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 146

147 55-147 Thread Cutting Produces a helical ridge of uniform section on workpiece Performed by taking successive cuts with threading toolbit of same shape as thread form required Work may be held between centers or in chuck 147

148 Procedure to Set Up a Lathe for Threading (60º Thread)
55-148 Procedure to Set Up a Lathe for Threading (60º Thread) Set lathe speed to ¼ speed used for turning Set quick-change gearbox for required pitch in threads per inch or in millimeters Engage lead screw Secure 60º threading toolbit and check angle using thread center gage Set compound rest at 29º to right; set to left for left-hand thread 148

149 Set cutting tool to height of lathe center point
55-149 Set cutting tool to height of lathe center point Mount work between centers Make sure lathe dog is tight on work If work mounted in chuck, it must be held tightly Set toolbit at right angles to work, using thread center gage Arrange apron controls to allow split-nut lever to be engaged 149

150 Thread-Cutting Operation
55-150 Thread-Cutting Operation Procedure to cut a 60º thread Check major diameter of work for size Start lathe and chamfer end of workpiece with side of threading tool to just below minor diameter of thread Mark length to be threaded by cutting light groove at this point with threading tool while lathe revolving 150

151 Turn compound rest handle until threading tool lightly marks work
55-151 Move carriage until point of threading tool near right-hand end of work Turn crossfeed handle until threading tool close to diameter, but stop when handle is at 3 o'clock position Hold crossfeed handle in this position and set graduated collar to zero Turn compound rest handle until threading tool lightly marks work 151

152 Move carriage to right until toolbit clears end of work
55-152 Move carriage to right until toolbit clears end of work Feed compound rest clockwise about .003 in. Engage split-nut lever on correct line of thread-chasing dial and take trial cut along length to be threaded At end of cut, turn crossfeed handle counterclockwise to move toolbit away from work and disengage split-nut lever 152

153 Set depth of all threading cuts with compound rest handle
55-153 Stop lathe and check number of tpi with thread pitch gage, rule, or center gage After each cut, turn carriage handwheel to bring toolbit to start of thread and return crossfeed handle to zero Set depth of all threading cuts with compound rest handle See Table 55.2 and Table 55.3 153

154 55-154 When tool is fed in at 29º, most of the cutting is done by the leading edge of toolbit. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

155 Table 55.2 Depth settings for cutting 60° national form threads*
55-155 Table 55.2  Depth settings for cutting 60° national form threads* Compound Rest Setting tpi 0° 30° 29° Portion of table taken from textbook

156 Remove burrs from top of thread with file
55-156 Apply cutting fluid and take successive cuts until top (crest) and bottom (root) of thread are same width Remove burrs from top of thread with file Check thread with master nut and take further cuts 156

157 Six Ways to Check Threads
55-157 Six Ways to Check Threads Depends on accuracy required: Master nut or screw Thread micrometer Three wires Thread roll or snap gage Thread ring or plug gage Optical comparator 157


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