More from s m aher

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= : eran rs Free Hand Sketches, , a, , ®, , 10., ll,, , 7.4, , , , , , , , , , , , , , , , , , , , , , , , , , , , Nut, , , , Root or core, , Fig. 7.1 :.Screw threads, , Crest : The crest is the outermost part of thread., Root : The root is the inner-most part of thread., Flank : The surface between crest and root is called as flank of the thread., Angle of thread : It is the angle between flanks of the, , Depth of thread : It is the distance between, to the axis of the screw., , thread measured on an axial plane., crest and root of the thread measured perpendicular, , Nominal Diameter : It is the diameter of the cylindrical piece on which the thread is cut., Generally the screw is specified by this diameter., , Crest or major diameter : It is the largest diameter of the screw at the crest of the thread. It is, also called as outside diameter., , Root or minor diameter : It is the smallest diameter of the screw at the root or core of the thread., It is also called as core diameter., , Pitch (p) : It is the distance measured along the axis of thread from a point on the thread to a, corresponding point on the next thread i.e. from crest to crest or root to root., , Lead (L) : It is the distance moved by a nut in the axial direction in one complete revolution,, Slope : The slope of thread is equal to half the lead of the screw thread., , Multiple-start Threads :, , The screw thread can be single-start, double-start, triple-start or multiple-start thread. In single, Start thread, the pitch and the lead of the thread are same. When a nut is required to move a considerably, read, the pitc : scieit, long axial distance in one revolution, the multiple-start thread is us, , In double-start thread the lead is twice the pitch. In triple-start thread the lead is three times the, nN double-s, , i tion., Pitch. In general the lead and pitch are related by the following equation, , Lead = Pitch x Number of starts

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7.5 Right-hand and Left-hand Threads :, , When bolt is rotated in clockwise direction it, advances in nut, then the thread is known as, right-hand thread. When bolt is come out from nut, , when it rotates in clockwise direction, then thread is, , Clockwise, known as left-hand threads. etetion of bol, , , , Fig. 7.3, , When the bolt is kept horizontal then in case of right-hand thread the thread slopes res etn, from left to right and incase of left-hand thread it slopes downward from right to left as shown in, Fig. 7.4., , , , (a) Right-hand thread (b) Left-hand thread, Fig. 7.4, , 7.6 Conventional Representation of Threads :, , To draw actual helical form of screw thread it would take considerable time, therefore in actual, practice threads are usually represented by conventionally., , MSBTE

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Engineering Drawing (Diploma), 7.6.1. External Thread :, , , , Free Hand Sketches, , Minor or root, diameter, , , , , , CH, , Detailed Schematic Simplified Symbol, , , , , , , , , , , , , , , , , , , , Fig. 7.5 : External threads, 7.6.2 Internal Thread :, , The internal threads are conventionally shown by means of one continuous thick and thin lines, indicating minor and major diameters respectively. In side view of internal thread the major or outside, , diameter is represented by a part of a continuous thin-line circle about three quarters of the, circumference as shown in Fig. 7.6., , Major or, _outside diameter, , !, , l, meee,, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , T, Detailed Schematic Section Unsectioned Symbol, simplified, , Fig. 7.6 : Internal threads, , 7.7. Forms of Screw Threads :, , The various forms of screw threads are shown, , , , in following table 7.1., Description, These threads have coarse pitch which gives, , effective leak-proof joint. They form V thread with, angle of thread 55° with rounded off at the crest, , and the roots., , , , Forms of thread, British Standard with Worth threads (BSW), , , , aio

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Free Hand Sketches, , , , , , , , , , , , , , , , Engineering Drawing (Diploma) 7-6, Forms of thread Description, British Association thread (BA) This is a modification of BSW thread with fine, pitches and thread angle of 47.5°. They are used, , 3 for precision work. They are stronger as compared, &, © to BSW thread., oo) a, oO, 3, 8, 3, , , , , , , , , , , , , , , , , , These threads have a flat crest and root. The flat, crest can withstand more rough usage than sharp Vv, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ae threads. This form of thread is also known as, f American National Thread. ., 3} a, aie, These threads are standardized by the International, Organization for Standardization (ISO) and are, available in inch and metric series. The threads are, ae rounded at roots for both external and internal, thread and the crests are made flat. The angle of, =e thread:is 60°., Olt, Ole, 30) a, D=0.86PX ORT O61 P Ale Y, External, Square thread As the name suggests, the flanks of threads are, , , , , , , , , , , , , , , , , , , , , , , , right angles to the axis of thread. They are, generally used for power transmission (e.g. in, Screw jack, lead screws of lathes)

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ey, , Description p=, These threads are modification of square thread., The angle of thread is 29°. These threads are much, stronger than square thread and easy, manufacture. These threads are used in bench, vices., , , , , , , , These threads have completely rounded at top and, bottom and are easy to cast or roll. It is not, economically to manufacture it on machine. They, are used in railway couplings where rough usage, and heavy wear is there. They also used in necks, of bottles., , , , , , , , , , , , , , , , , , , , , , , , , , , , , , In this type of thread one flank is perpendicular to, axis of thread and one flank is inclined at 45° to it., These threads are used to transmit the power in, one direction only., , The ISO metric threads are completely, standardized and are used commonly in industry., The metric thread is designed by the letter M, followed by the nominal diameter e.g. M20, indicates metric thread with 20 mm as nominal, diameter of thread.