11 Threaded Fasteners_1.ppt

8/16/2019 11 Threaded Fasteners_1.ppt

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Chapter 11 ThreadedFasteners

• Two Basic types of fasteners: Permanent & removable

• Permanent- Examples: ivets & welds

• emovable- Examples: bolts! screws! n"ts! pins! rin#s $eys

• %tandardiation red"ces the costs of fasteners

• ' p"rposes – To hold parts to#ether

– To ad("st

– To transfer power



%crew Threads

• )e*nition: a %CE+ T,E) is a rid#e of "niform sectionin the form of a helix on the external or internal s"rface of acylinder

• )e*nition: the P.TC, of a thread P is the distance from a

point on the thread form to the correspondin# point on thenext form! meas"red parallel to the axis

• )e*nition: the /E) / is the distance the threaded partwo"ld move parallel to the axis d"rin# one completerotation in relation to a *xed matin# part 0the distance a

screw wo"ld enter a threaded hole in one t"rn



THREADED FASTENERS

%CE+ T,E) TE2%



THREADED FASTENERS

T,E) F32%



THREADED FASTENERS

T,E) F32%



Three types of threadrepresentation "sed on

wor$in# drawin#s• %impli*ed

• )etailed

•

%chematic



i#ht- and /eft-,and threads

• Threads are ass"med to be ri#hthand "nless otherwise desi#nated

• bolt bein# threaded into a tappedhole wo"ld be t"rned in a ri#ht-hand0cloc$wise direction



THREADED FASTENERS

.4,T- 5) /EFT-,5) T,E)%



THREADED FASTENERS

%.54/E T,E)

/E) 6 1P



THREADED FASTENERS

)37B/E T,E)

/E) 6 8P



THREADED FASTENERS

T.P/E T,E)

/E) 6 'P



.nch Threads

• )e*nition: P.TC, 619threads per inch

• )e*nition: T,E) %E.E% are forfasteners with di;erent diameters and

the same threads per inch

• 75C 7ni*ed Co"rse Thread %eries

• 75F 7ni*ed Fine Thread %eries 0Table

appendix

• 75EF extra *ne thread series



THREADED FASTENERS

B%.C T,E) C//37T



Thread Class1!8!' External1B!8B!'B .nternal

• 1!1B: loosest *t

• 8!8B: ordinary #ood #rade ofcommercial prod"ct

• '!'B: ,i#h-#rade commercial prod"cts

• Example: <=>?-1? 75C-8 class of *t• 5ominal )iameter thread series

threads9inch0)iameter! threads9inch! thread form & series!

class of *t



THREADED FASTENERS

E@TE5/ T,E)%



THREADED FASTENERS

B/.5) ,3/E .5TE5/ T,E)



2etric Threads• )e*nition: Pitch for metric threads is the distance between

correspondin# points on ad(acent teeth<• Co"rse-thread is intended for #eneral en#ineerin# wor$ and

commercial applications

• Fine-thread series is for #eneral "se< Compared with coarse! a*ne-thread screw is stron#er in both tensile and torsional stren#th

• )e*nition: the F.T of a screw thread is the amo"nt of clearancebetween the internal and external threads when they areassembled

• Tolerance #rades: the lar#er the n"mber! the lar#er the tolerance

– Tolerance position e 0lar#e allowance

– Tolerance position # 0small allowance

–

Tolerance position h 0no allowance – For internal threads:

• Tolerance position 4 0small allowance

• Tolerance position , 0no allowance



THREADED FASTENERS

B%.C T,E) C//37T

2ET.C T,E)%



.%3 2etric %crew Thread)esi#nation

• 5ominal sie 0basic ma(or diameterand pitch expressed in millimeters<

• Example: 21A x 1<> >#A#

2etric desi#nation 5ominal diameter Pitch Tolerance position &

#rade

• Example: 21? x 1<> x 8>

1?mm 1<> pitch 8> mm lon#

• Example: 21A 0pitch may be omitted for coarse threads



2etric Threads contin"ed

• For external threads! the len#th of the threadmay be #iven as a dimension of the drawin#<

• For threaded holes that #o all the waythro"#h the part! the term T,7 issometimes added

• .f no depth is #iven! the hole is ass"med to#o T,7

•

For threaded holes that do not #o all the waythr"! the depth is #iven in a note 0minim"mdepth of f"ll thread Ex< 218 x 1<=> x 8?



Pipe Threads

• .nch: D-5PT or D 5PT

• 2etric: D .5< 5PT or D .5<-5PT

•

5ominal diameter and pipe thic$nessspecify inch-sied pipe 0typical• D6nominal diameter

• 6n"mber of threads9inch

•

56merican %tandard• P6pipe

• %6strai#ht pipe thread

• T6taper pipe thread

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11 Threaded Fasteners_1.ppt