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