5.1 INTRODUCTIONA machine element used for holding or joining two or more parts of a machine or structure isknown as a fastener. The process of joining the parts is called fastening. The fasteners are of twotypes : permanent and removable (temporary). Riveting and welding processes are used for fasteningpermanently. Screwed fasteners such as bolts, studs and nuts in combination, machine screws,set screws, etc., and keys, cotters, couplings, etc., are used for fastening components that requirefrequent assembly and dissembly.Screwed fasteners occupy the most prominent place among the removable fasteners. Ingeneral, screwed fasteners are used : (i) to hold parts together, (ii) to adjust parts with referenceto each other and (iii) to transmit power.5.2 SCREWTHREADNOMENCLATUREAscrewthreadisobtainedbycuttingacontinuoushelicalgrooveonacylindricalsurface(external thread). The threaded portion engages with a corresponding threaded hole (internalthread);formingascrewedfastener.Followingarethetermsthatareassociatedwithscrewthreads(Fig.5.1).Angle of threadPMinordia.Pitchdia.Majordia.CrestRootFlankFig.5.1Screwthreadnomenclature1. Major (nominal) diameterThis is the largest diameter of a screw thread, touching the crests on an external thread or theroots of an internal thread.2. Minor (core) diameterThis is the smallest diameter of a screw thread, touching the roots or core of an external thread(root or core diameter) or the crests of an internal thread.5 SCREWED FASTENERS77dharmd:\N-Design\Des5-1.pm578 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrint3. Pitch diameterThis is the diameter of an imaginary cylinder, passing through the threads at the points wherethe thread width is equal to the space between the threads.4. PitchIt is the distance measured parallel to the axis, between corresponding points on adjacent screwthreads.5. LeadIt is the distance a screw advances axially in one turn.6. FlankFlank is the straight portion of the surface, on either side of the screw thread.7. CrestIt is the peak edge of a screw thread, that connects the adjacent flanks at the top.8. RootIt is the bottom edge of the thread that connects the adjacent flanks at the bottom.9. Thread angleThis is the angle included between the flanks of the thread, measured in an axial plane.5.3 FORMSOFTHREADSBureau of Indian Standards (BIS) adapts ISO (International Organisation for Standards) metricthreads which are adapted by a number of countries apart from India.The design profiles of external and internal threads are shown in Fig. 5.2. The followingaretherelationsbetweenthevariousparametersmarkedinthefigure:0.125PThe root is rounded and clearedbeyond a width of 0.125PDD2D1H10.25HInternalthreads60PR0.5 P0.25 Hd3d2dh30.5H0.5HH0.125HInternal thread diametersD - Major diameterD- Pitch diameterD- Minor diameter21External thread diametersd - Major diameter- Pitch diameter- Minor diameter2dd30.167HExternalthreads60Fig. 5.2 Metric screw threadP = Pitch d3 = d2 2 (H/2 H/6)H = 0.86 P = d 1.22PD = d = Major diameter H1 = (D D1)/2 = 5H/8 = 0.54P D2 = d2 = d 0.75H h3 = (d d3)/2 = 17/24H = 0.61P D1 = d2 2(H/2 H/4) = d 2H1 R = H/6 = 0.14PScrewedFasteners 79dharmd:\N-Design\Des5-1.pm5 SeventhPrint= d 1.08PIt may be noted from the figure that in order to avoid sharp corners, the basic profile is roundedat the root (minor diameter) of the design profile of an external thread. Similarly, in the case ofinternal thread, rounding is done at the root (major diameter) of the design profile.5.3.1Other Thread ProfiIesApartfromISOmetricscrewthreadprofile,thereareotherprofilesinusetomeetvariousapplications. These profiles are shown in Fig. 5.3, the characteristics and applications of whichare discussed below :..7.7 1-Tnreoo Jsnorp)This thread profile has a larger contact area, providing more frictional resistance to motion.Hence, it is used where effective positioning is required. It is also used in brass pipe work...7.2 BrI1Isn S1onooro WnI1wor1n JB.S.W) TnreooThis thread form is adopted in Britain in inch units. The profile has rounded ends, making it lessliable to damage than sharp V-thread...7. Bu11ress TnreooThis thread is a combination of V-and square threads. It exhibits the advantages of square thread,like the ability to transmit power and low frictional resistance, with the strength of the V-thread.It is used where power transmission takes place in one direction only such as screw press, quickacting carpenters vice, etc...7.4 Squore TnreooSquare thread is an ideal thread form for power transmission. In this, as the thread flank is atright angle to the axis, the normal force between the threads, acts parallel to the axis, with zeroradial component. This enables the nut to transmit very high pressures, as in the case of a screwjack and other similar applications...7. ACME TnreooIt is a modified form of square thread. It is much stronger than square thread because of the widerbase and it is easy to cut. The inclined sides of the thread facilitate quick and easy engagement anddisengagement as for example, the split nut with the lead screw of a lathe...7. Worm TnreooWorm thread is similar to the ACME thread, but is deeper. It is used on shafts to carry power towormwheels.60P0.87PSharp Vr = .14 P P55r0.64PWhitworth0.66P0.16 PP457Buttress0.5P0.5PPSquare290.37 P0.5P0.5PPACME29P0.34 P0.69PWormFig. 5.3 Types of thread profiles80 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrint5.4 THREADSERIESBIS recommends two thread series: coarse series and fine series, based on the relative values ofthe pitches. However, it must be noted that the concept of quality is not associated with theseterms. For any particular diameter, there is only one largest pitch, called the coarse pitch and therest are designated as fine pitches.Table 5.1 gives the nominal diameter and pitch combinations for coarse and fine series ofISO metric screw threads.Table 5.1Diameter-pitch combination for ISO metric threadsNominal diameter PitchFirst Second Finechoice choice Coarse1 2 32 0.4 0.25 2.2 0.45 0.25 2.5 0.45 0.35 3 0.5 0.35 3.5 0.6 0.35 4 0.7 0.5 4.5 0.75 0.5 5 0.8 0.5 6 1 0.75 0.5 8 1.25 1 0.75 10 1.5 1.25 1 0.7512 1.75 1.5 1.25 16 14 2 1.5 1 20 18,22 2.5 2 1.5 124 27 3 2 1.5 130 33 3.5 2 1.5 136 39 4 3 2 1.542 45 4.5 4 3 248 52 5 4 3 256 60 5.5 4 3 264 68 6 4 3 272 76 6 4 3 280 85 6 4 3 290 95 6 4 3 2100 6 4 3 2105to300 6 4 3ScrewedFasteners 81dharmd:\N-Design\Des5-1.pm5 SeventhPrint5.5 THREADDESIGNATIONThe diameter-pitch combination of an ISO metric screw thread is designated by the letter Mfollowed by the value of the nominal diameter and pitch, the two values being separated by thesign . For example, a diameter pitch combination of nominal diameter 10 mm and pitch 1.25mm is designated as M10 1.25.If there is no indication of pitch in the designation, it shall mean the coarse pitch. Forexample, M 10 means that the nominal diameter of the thread is 10 mm and pitch is 1.5 mm.Followingaretheotherdesignations,dependingontheshapeofthethreadprofile:SQ 40 10 SQUARE thread of nominal diameter 40 mm and pitch 10 mmACME 40 8 ACME thread of nominal diameter 40 mm and pitch 8 mmWORM 40 10 WORM thread of nominal diameter 40 mm and pitch 10 mm5.6 MULTI-STARTTHREADSA single-start thread consists of a single, continuous helical groove for which the lead is equal tothe pitch. As the depth of the thread depends on the pitch, greater the lead desired, greater will bethe pitch and hence smaller will be the core diameter, reducing the strength of the fastener. Toovercome this drawback, multi-start threads are recommended.Figure 5.4 shows single and double-start threads of V-and square profiles.LL0.5PP(a) V-threadsP0.5PP0.5PDH H H HDP0.5PP0.5PLL0.5PP(b) Square threadsP0.5PP0.5PDH HH HDP0.5PP0.5PFig.5.4Singleandmult-startthreadsIn multi-start threads, lead may be increased by increasing the number of starts, withoutincreasing the pitch. For a double start thread, lead is equal to twice the pitch and for a triplestart thread, lead is equal to thrice the pitch.In double start threads, two threads are cut separately, starting at points, diametricallyopposite to each other. In triple start threads, the starting points are 120 apart on the circumferenceof the screws.Multi-start threads are also used wherever quick action is desired, as in fountain pens,automobile starters, arbor press spindles, hydraulic valve spindles, etc.5.7 RIGHTHANDANDLEFTHANDTHREADSScrew threads may be right hand or left hand, depending on the direction of the helix. A righthand thread is one which advances into the nut, when turned in a clockwise direction and a lefthand thread is one which advances into the nut when turned in a counter clockwise direction. Anabbreviation LH is used to indicate a left hand thread. Unless otherwise stated, a thread should beconsidered as a right hand one. Figure 5.5 illustrates both right and left hand thread forms.82 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrintAdvancesTurn counterclockwiseLeft handAdvancesTurn clockwiseRight handFig. 5.5Right hand and left hand threads5.7.1CoupIer-nutA coupler-nut or turnbuckle is an example of a machine element, in which both right hand andleft hand thread forms are used. The length of a tie rod, may be adjusted by this device. Referringthe Fig. 5.6a ; out of the two rods operating inside the nut (a long double nut), one will have aright hand thread at its end and the other, a left hand one. The nut is usually hexagonal at itsouter surface, with a clearance provided at the centre. By turning the nut, the two rods in it maymove either closer together, or away from each other. Figure 5.6b shows a coupler used for railwaycoaches.Theyarealsousedforfixingguywires,etc.60 55 35129560 60 170 351295(a) Adjustable joint for round rods15KNURLEDSQ THD 8 (LH) 50 36120 120 70(b) Coupler for railway coachesSQ THD 8(RH) 40Fig. 5.65.8 REPRESENTATIONOFTHREADSThe true projection of a threaded portion of a part consists of a series of helices and it takesconsiderable time to draw them. Hence it is the usual practice to follow some conventional methodsto represent screw threads. Figure 5.1 shows the true projection of a screw thread, whereas theconventional representation of external and internal threads as recommended by BIS is shown inFig.5.7.ScrewedFasteners 83dharmd:\N-Design\Des5-1.pm5 SeventhPrintIt may be noted from Fig. 5.7, that the crests of threads are indicated by a continuous thickline and the roots, by a continuous thin line. For hidden screw threads, the crests and roots areindicated by dotted lines. For threaded parts in section, hatching should be extended to the linedefining the crest of the thread. In the view from side, the threaded roots are represented by aportion of a circle, drawn with a continuous thin line, of length approximately three-quarters ofthe circumference.The limit of useful length of screw threads is represented by a continuous thick line or adotted line, dependingon its visibility. The length upto which the incomplete threads are formedbeyond the useful limit, is known as a run-out. It is represented by two inclined lines.The simplified representation, though it saves time, is not an effective method to conveythread forms. The schematic representation, used for the purpose is shown in Fig. 5.8. In practice,the schematic representation is followed for only visible threads, i.e., for external threads andinternal threads in section. From the Fig. 5.8, it may be observed that the crest diameters, bothin external and internal threads, are drawn by thick lines. Further, the crests are represented bythin lines, extending upto the major diameter and the roots by thick lines, extending upto theminor diameter, these lines being drawn inclined with a slope equal to half the pitch.Fig.5.7Conventionalrepresentationofthreads84 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrintFig. 5.9 illustrates the schematic representation of square threads.DHHP 0.5 PP 0.5 PFig.5.8SchematicrepresentationofthreadedpartsV-threadsP0.5 P0.5 PP(a)(b)HHDFig.5.9SchematicrepresentationofthreadedpartsSquarethreads5.8.1Representation of Threaded Parts in AssembIyFigure5.10ashowstheschematicrepresentationandFigs.5.10bandc,theconventionalrepresentationofthreadsinengagement.Figure5.10arepresentstheinternalthreadedpartinsection;however,theexternalthreadedoneisshownunsectioned.InFigs.5.10bandc,theexternalthreadedpartsareshowncoveringtheinternalthreadedpartsandshouldnotbeshownashiddenbythem.ScrewedFasteners 85dharmd:\N-Design\Des5-1.pm5 SeventhPrint(a) (b) (c)Fig.5.10Externalandinternalthreadsinengagement5.9 BOLTEDJOINTA bolt and nut in combination (Fig. 5.11) is a fasteningdeviceusedtoholdtwopartstogether.Thebodyofthe bolt, called shank is cylindrical in form, the head;squareorhexagonalinshape,isformedbyforging.Screw threads are cut on the other end of the shank.Nutsingeneralaresquareorhexagonalinshape.Thenutswithinternalthreadsengagewiththecorrespondingsizeoftheexternalthreadsofthebolt.However,thereareotherformsofnutsusedtosuitspecificrequirements.Fornuts,hexagonalshapeispreferredtothesquareone,asitiseasytotighteneveninalimitedspace.Thisisbecause,withonlyone-sixthofaturn,thespannercanbere-introducedinthesameposition.However,squarenutsareusedwhenfrequentlooseningandtighteningisrequired,forexampleonjobholdingdeviceslikevices,toolpostsinmachines,etc.Thesharpcornersontheheadofboltsandnutsareremovedbychamfering.5.9.1Methods of Drawing HexagonaI (BoIt Head ) NutDrawing hexagonal bolt head or nut, to the exact dimensions is labourious and time consuming.Moreover, as standard bolts and nuts are used, it is not necessary to draw them accurately. Thefollowing approximate methods are used to save the draughting time :Method 1 (Fig. 5.12)Empirical relations :Major or nominal diameter of bolt = DThickness of nut, T = DWidth of nut across flat surfaces,W = 1.5D + 3 mmRadius of chamfer, R = 1.5DFig. 5.11 Bolted joint86 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrintDW1412 11 10R2R2R DR1 2 4 38 6 1 7 9R1513Fig. 5.12 Method of drawing views of a hexagonal nut (Method I)24+-,74-1. Drawtheviewfromabovebydrawingacircleofdiameter,Wanddescribearegularhexagon on it, by keeping any two parallel sides of the hexagon, horizontal.2. Project the view from the front, and the view from side, and mark the height equal to D.3. With radius R, draw the chamfer arc2-1-3 passing through the point 1 in the front face.4. Mark points 4 and 5, lying in-line with 2 and 3.5. Locate points 8,9 on the top surface, by projecting from the view from above.6. Draw the chamfers 48and 59.7. Locate points 6 and 7, lying at the middle of the outer two faces.8. Draw circular arcs passing through the points 4, 6, 2 and 3, 7, 5, after determining theradius R1 geometrically.9. Project the view from the side and locate points 10, 11 and 12.10. Mark points 13 and 14, lying at the middle of the two faces (view from the side).11. Draw circular arcs passing through the points 10, 13, 11 and 11, 14, 12, after determiningthe radius R2 geometrically.It may be noted that in the view from the front, the upper outer corners appear chamfered.In the view from the side, where only two faces are seen, the corners appear square.Method 2 (Fig. 5.13)Empirical relations :Majorornominaldiameterofbolt = DThicknessofnut,T = DScrewedFasteners 87dharmd:\N-Design\Des5-1.pm5 SeventhPrintWidthofthenutacrosscorners = 2 DRadiusofchamferarc,R = 1.5 DFigure5.13illustratesthestagesofdrawingdifferentviewsofahexagonalnut,followingtheaboverelations,whichareself-explanatory.DD2 DR2 R2R1R1R(a)D(b)Fig. 5.13 Method of drawing views of a hexagonal nut (Method II)The above method may be followed in routine drawing work, as it helps in drawing theviews quickly.5.9.2Method of Drawing Square (BoIt Head) NutA square bolt head and nut may be drawn, showing either across flats or corners. Followingrelations may be adopted for the purpose:88 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrintMajorornominaldiameterofbolt = DThicknessofnut,T = DWidthofthenutacrossflats,W = 1.5 D + 3 mmRadiusofchamferarc,R = 2 DFigure 5.14 illustrates the method of drawing views of a square nut, in two orientations.WDRDDR1RDWFig.5.14 Method of drawing the views of a square nut5.9.3HexagonaI and Square Headed BoItsFigure 5.15 shows the two views of a hexagonal headed bolt and square headed bolt, with theproportions marked.2D2 D0.75 D LD(a) Hexagonal headed boltW2 D0.75 D LD(b) Square headed boltFig. 5.15ScrewedFasteners 89dharmd:\N-Design\Des5-1.pm5 SeventhPrint5.9.4WashersA washer is a cylindrical piece of metal with a hole toreceive the bolt. It is used to give a perfect seating forthe nut and to distribute the tightening force uniformlyto the parts under the joint. It also prevents the nutfromdamagingthemetalsurfaceunderthejoint.Figure 5.16showsawasher,withtheproportionsmarked.Figure 5.17 illustrates the views of a hexagonalheaded bolt with a nut and a washer in position.2D2D+40.15 D2 DDD0.75 DLFig. 5.17 A hexagonal headed bolt with a nut and a washer in position5.9.5Other Forms of BoIts.P..7 Squore Heooeo BoI1 wI1n Squore AecRIt is provided with a square neck, which fits into a corresponding square hole in the adjacent part,preventingthe rotation of the bolt (Fig. 5.18).D2D1.5D+30.8 D 0.8 DFig. 5.18 Square headed bolt with square neckFig. 5.16 Washer0.15 D2D+4D + 190 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrint.P..2 T-Heooeo BoI1 WI1n Squore AecRIn this, a square neck provided below the head, prevents the rotation of the bolt. This type of bolt isused for fixing vices, work pieces, etc., to the machine table having T-slots (Fig. 5.19).0.8 D 0.8 DD1.8D 0.8 D0.9 DDFig. 5.19 T-headed boltFig. 5.20 Hook bolt.P.. HooR BoI1This bolt passes through a hole in one part only, while the other part is gripped by the hookshaped bolt head. It is used where there is no space for making a bolt hole in one of the parts. Thesquare neck prevents the rotation of the bolt (Fig. 5.20)..P..4 Eye BoI1In order to facilitate lifting of heavy machinery, like electric generators, motors, turbines, etc.,eye bolts are screwed on to their top surfaces. For fitting an eye bolt, a tapped hole is provided,above the centre of gravity of the machine (Fig. 5.21).0.8 D2 D0.4D2D1.5D1.5DDFig. 5.21 Eye-boltScrewedFasteners 91dharmd:\N-Design\Des5-1.pm5 SeventhPrint.P.. S1uo BoI1 or S1uoIt consists of cylindrical shank with threads cut on both the ends (Fig. 5.22a). It is used wherethere is no place for accommodating the bolt head or when one of the parts to be joined is too thickto use an ordinary bolt.The stud is first screwed into one of the two parts to be joined, usually the thicker one. Astuddriver,intheformofathickhexagonalnutwithablindthreadedholeisusedforthepurpose. After placing the second part over the stud, a nut is screwed-on over the nut end. It isusual to provide in the second part, a hole which is slightly larger than the stud nominal diameter.Figure 5.22b shows a stud joint.DPlateMaincastingD2 DNutendStudendPlainpart(a) (b)Fig.5.22(a)Stud, (b)Studjoint5.9.6Other Forms of Nuts.P..7 FIongeo Au1This is a hexagonal nut with a collar or flange, provided integral with it. This permits the use ofa bolt in a comparitively large size hole (Fig. 5.23a)..P..2 Cop Au1It is a hexagonal nut with a cylindrical cap at the top. This design protects the end of the bolt fromcorrosion and also prevents leakage through the threads. Cap nuts are used in smoke boxes orlocomotive and steam pipe connections (Fig. 5.23b)..P.. Oome Au1It is another form of a cap nut, having a spherical dome at the top (Fig. 5.23c)..P..4 Cops1on Au1This nut is cylindrical in shape, with holes drilled laterally in the curved surface. A tommy barmay be used in the holes for turning the nut (Fig. 5.23d). Holes may also be drilled in the upperflat face of the nut.92 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrintD2.2 DD0.25Da - Flanged nut1.5 D + 30.5DD0.25DDb - Cap nutDD0.5Dc - Dome nut1.8 D0.5DDDD0.1D0.5D1.8 D1.5 DD2 D0.4D0.6 D1.5 D1.2 DD0.2D0.2Dd - Capstan nut0.2De - Ring nut f - Wing nut0.2DFig. 5.23 Other forms of nuts.P.. SIo11eo or RIng Au1This nut is in the form of a ring, with slots in the curved surface, running parallel to the axis. Aspecial C-spanner is used to operate the nut. These nuts are used on large screws, where the useof ordinary spanner is inconvenient (Fig. 5.23e)..P.. WIng Au1This nut is used when frequent removal is required, such as inspection covers, lids, etc. It isoperated by the thumb (Fig. 5.23f).5.9.7Cap Screws and Machine ScrewsCap screws and machine screws are similar in shape, differing only in their relative sizes. Machinescrews are usually smaller in size, compared to cap screws. These are used for fastening twoparts, one with clearance hole and the other with tapped hole. The clearance of the unthreadedhole need not be shown on the drawing as its presence is obvious. Figure 5.24 shows differenttypes of cap and machine screws, with proportions marked.ScrewedFasteners 93dharmd:\N-Design\Des5-1.pm5 SeventhPrint2 D0.6DL DD0.6D0.2D900.2 DLHexagonal head Flat head0.6D0.4D0.2 DD LRound headD1.5 D0.2 D0.6DLCheese headDOval head0.6DLR = 2.25 D0.2 D900.4DDDL 0.75D1.5 D30Socket headFig.5.24 TypesofmachineandcapscrewsCap screws are produced in finish form and are used on machines where accuracy andappearance are important. As cap screws are inferior to studs, they are used only on machinesrequiring few adjustments and are not suitable where frequent removal is necessary. These areproduced in different diameters, upto a maximum of 100 mm and lengths 250 mm.Machine screws are produced with a naturally bright finish and are not heat treated. Theyare particularly adopted for screwing into thin materials and the smaller ones are threadedthroughout the length. They are used in fire-arms, jigs, fixture and dies. They are produced indifferent diameters upto a maximum of 20 mm and lengths upto 50 mm.#'&5AJ5?HAMITheseareusedtopreventrelativemotionbetweentworotatingparts,suchasthemovementofpulleyonshaft.Forthis,asetscrewisscrewedintothepulleyhubsothat its end-point bears firmly against the shaft (Fig. 5.25).Thefasteningactionisbyfrictionbetweenthescrewandtheshaft.Setscrewsarenotefficientandsoareusedonlyfortransmittingverylightloads.Forlongerlife,setscrewsaremadeofsteelandcasehardened.Further,for better results, the shaft surface is suitably machinedforprovidingmoregrip,eliminatinganyslippingtendency.Figure5.26showsdifferentformsofsetscrews.Fig. 5.250.25DDL94 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrint5.10 LOCKINGARRANGEMENTSFORNUTSTheboltedjoints,thoughremovableinnature,arerequiredtostayfirmwithoutbecomingloose,oftheirownaccord.However,thejointsusedinthemovingpartsofamachinery,maybesubjectedtovibrations.Thismayslackenthejoint,leadingtoseriousbreakdown.Toeliminatetheslackeningtendency,differentarrangements,asdiscussedfurther,areusedtolockthenuts:5.10.1 Lock NutThisisthemostcommonlyusedlockingdevice.Inthisarrangement,asecondnut,knownaslocknutisusedincombinationwithastandardnut(Fig.5.27a).Thethicknessofalocknutisusuallytwo-thirdsD,whereDisthemajordiameterofthebolt.Thelocknutisusuallyplacedbelowthestandardnut.Tomakethejoint,thelocknutisfirstscrewedtightlyandthenthestandardnutistightenedtillittouchesthelocknut.Afterwards,thelocknutisthenscrewedbackonthestandardnut,whichisheldbyaspanner.Thethreadsofthetwonutsbecomewedgedbetweenthethreadsofthebolt.D1.8 D0.8DD1.5 D0.2 D0.6DD1.5 D45D1.5 D0.5DDD D0.5Da Set screw heads b Grub screwsDDD30D450.6 DD0.6D12045D0.8D0.2Dc Set screw endsRFig. 5.262 D0.67DD(a) (b) (c)Fig. 5.27 Lock nutScrewedFasteners 95dharmd:\N-Design\Des5-1.pm5 SeventhPrintWhenthelocknutisfirstscrewedintoitsposition,thetopflanksofitpressagainstthebottomflanksofthebolt(Fig.5.27b).Figure5.27cshowstheconditionbetweentheflanks of the nuts and the bolt, when the second nut is locked in position. It may be observedthatinthisposition,thetopflanksofthetopnut,pressagainstthebottomflanksofthebolt,whereas,thebottomflanksofthelocknutpressagainstthetopflanksofthebolt.5.10.2LockingbySpIitPinAsplitpin,madeofsteelwireofsemi-circularcross-sectionisusedforlockingthenut.Inthis arrangement, the split pin is inserted through a hole in the bolt body and touching justthetopsurfaceofthenut.Then,theendsofthepinaresplitopentopreventitfromcoming out while in use (Fig. 5.28).5.10.3LockingbyCastIeNutA castle nut is a hexagonal nut with a cylindrical collar turned on one end. Threads are cutinthenutportiononlyandsixrectangularslotsarecutthroughthecollar.Asplitpinisinsertedthroughaholeintheboltbodyafteradjustingthenutsuchthattheholeinthebolt body comes in-line with slots. This arrangement is used in automobile works (Fig. 5.29).SPLIT PIN, DIA 0.2 DDD2 DSPLIT PIN, DIA 0.25 D1.25DD2 D0.3D0.05D450.45D3030SLOTS,WIDE 0.25 DFig. 5.28 Locking by split pinFig. 5.29 Castle nut96 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrint5.10.4 WiIe's Lock nutIt is a hexagonal nut with a slot, cut half-way across it. After tightening the nut in the usualmanner,asetscrewisusedfromthetopofthenut,compressingthetwoparts.Forthispurpose,theupperportionofthenutshouldhaveaclearanceholeandthelowerportiontapped(Fig.5.30).5.10.5 Locking by Set ScrewIn this arrangement, after the nut is tightened, a set screw in fitted in the part, adjoining thenut, so that it touches one of the flat faces of the nut. The arrangement prevents the looseningtendencyofthenut(Fig.5.31).2 D0.75 DDSCREW, DIA 0.25 DLONG 0.75 D0.5D0.15DDD2DDSCREW, DIA 0.2 DLONG 0.9 D Fig. 5.30 Wiles lock nut Fig. 5.31 Locking by set screw5.10.6 Grooved NutIthasacylindricalgroovedcollar,integrallyprovidedatthelowerendofthenut.Thiscollarfitsintoacorrespondingrecessintheadjoiningpart.Inthisarrangement,aftertighteningthenut,asetscrewisinsertedfromoneendoftheupperpart,sothattheendofthesetscrewentersthegroove,preventingthelooseningtendencyofthenut(Fig.5.32).5.10.7LockingbyScrewIn this, a cap nut with an integral washer and with a threaded hole in the cylindrical cap, isused. A corresponding tapped hole at the top end of the bolt is also required for the purpose.ScrewedFasteners 97dharmd:\N-Design\Des5-1.pm5 SeventhPrintInthisarrangement,asetscrewfittedthroughthecapandthroughtheboltend,preventsthelooseningtendencyofthenut,whenthepitchesofthemainnutandthesetscrewaredifferent(Fig.5.33).Thistypeofarrangementisusedforfittingthepropellerbladesonturbineshafts.SCREW,DIA 0.25 D0.25D0.25D0.2D2 D0.9DD1.5 D1.35 DD2.25 D0.3D0.15D0.4D0.9DSCREW, DIA 0.25 DLONG 0.85 D2 D1.5 D1.2 DFig. 5.32 Grooved nutFig. 5.33 Locking by screw5.10.8LockingbyPIateAlockingplateisgroovedsuchthatitfitsahexagonalnutinanyposition,atintervalsof30ofrotation.Itisfixedaroundthenut,bymeansofamachinescrew,asshowninFig.5.34.5.10.9LockingbySpringWasherInthisarrangement,aspringwasherofeithersingleordoublecoilisplacedunderthenutandtightened.Thespringforceofthewasherwillbeactingupwardsonthenut.Thisforcemakesthethreadsinthenutjammedontheboltthreads;thuspreventingthenutfromloosening(Fig. 5.35).98 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrint0.2DDSCREW,DIA 0.2 D + 2D2.1 D0.125DD2 DFig. 5.34 Locking by plate Fig. 5.35 Locking by spring washer5.11FOUNDATIONBOLTSFoundationboltsareusedforfixingmachinestotheirfoundations.Foundationboltsaremadebyforgingfrommildsteelorwroughtironrods.Theboltsizedependsuponthesizeofthemachineandthemagnitudeoftheforcesthatactonthemwhenthemachineisinoperation.Forsettingtheboltsinposition,theirpositionsaremarkedandthensuspendedintheholesmadeintheground.Afterwards,cementconcreteisfilledinthespacearoundinthebolts.Oncetheconcretesets;theboltsarefirmlysecuredtotheground.5.11.1EyeFoundationBoItThisisthesimplestformofallfoundationbolts.Inthis,oneendoftheboltisforgedintoan eye and a cross piece is fixed in it. Figure 5.36 shows an eye foundation bolt that is setinconcrete.5.11.2BentFoundationBoItAsthenameimplies,thisboltisforgedinbentformandsetincementconcrete.Whenmachines are to be placed on stone beds, the bolts are set in lead. Figure 5.37 shows a bentfoundation bolt that is set first in lead and then in cement concrete, resulting in a firm andstablebolt.5.11.3RagFoundationBoItThisboltconsistsofataperedbody,squareorrectangularincross-section,thetaperededgesbeinggrooved.Figure5.38showsaragfoundationboltthatissetfirstinleadandthenincementconcrete.ScrewedFasteners 99dharmd:\N-Design\Des5-1.pm5 SeventhPrintD0.1D15D2.5DD4 DD10D2.5D2DD Fig. 5.36 Eye foundation bolt Fig. 5.37 Bent foundation boltD2.5D10D2 DD6DFig. 5.38 Rag foundation bolt5.11.4LewisFoundationBoItThis is a removable foundation bolt. The body of the bolt is tapered in width on one side. Tousethisbolt,apitisproducedincementconcrete,byusinga(foundation)block.Oncetheconcretesets-in,theboltisplacedinitsothatthetaperedboltsurface,bearsagainstthetaperedfaceofthepit.Akeyistheninserted,bearingagainstthestraightsurfacesofthepitandthebolt.Thisarrangementmakestheboltfirminthebed.However,theboltmayberemovedbywithdrawingthekey(Fig.5.39).100 MachineDrawingdharmd:\N-Design\Des5-1.pm5 SeventhPrintD10D2.5D7.5DD1.67 D 0.67 DKeyKeyFig. 5.39 Lewis foundation boltThistypeoffoundationboltisnotcommonlyusedforfixingmachines.However,theprincipleisadvantageouslyusedforliftinghugestones.Forthis,agroove,similartothepitischiselledinthestoneandtheboltisfittedin.Thetopendoftheboltmaybeforgedintoaneyeandusedforliftingpurposes.5.11.5CotterFoundationBoItIt is used for fixing heavy machines. It has a rectangular slot at its bottom end, to receive acotter.Forputtingtheboltsinposition,thefoundationbedisfirstmade,providingholesforinsertingcotters.Figure5.40showsacotterfoundationboltinposition.Acastironwasher(W)placedasshown,providesbearingsurfaceforthecotter(C).1.5D0.4DDD0.4D 1.2D0.4D0.5D1.2DTHICK 0.25 DHand HoleWC3 DDFig. 5.40 Cotter foundation bolt