ME 114 Engineering Drawing II

Transcription

1 ME 114 Engineering Drawing II SCREW THREADS, BOLTS and NUTS Mechanica Engineering University of Gaziantep Dr. A. Toga Bozdana Assistant Professor

2 Threaded Fasteners Thread is the heica grooves which are opened to inner and outer surfaces. Fig. 1 shows the screw thread terminoogy. Externa thread (screw/vida - bot/cıvata - stud/sapama): A thread on the externa surface of a cyinder. Interna thread (nut/somun): A thread on the interna surface of a cyinder. Major diameter (diş üstü çap): The argest diameter of a screw thread. Minor diameter (diş dibi çap): The smaest diameter of a screw thread. Pitch diameter (böüm çapı): The diameter of an imaginary cyinder, the surface of which cuts the thread forms where the width of the thread and groove are equa. Figure 1 1

3 Threaded Fasteners Crest: The edge or surface that joins the sides of a thread and is farthest from the cyinder or cone from which the thread projects. Root: The edge or surface that joins the sides of adjacent thread forms and coincides with the cyinder or cone from which the thread projects. Depth of thread: The distance between crest and root measured norma to the axis. Pitch (hatve, adım): The distance between corresponding points on adjacent thread forms measured parae to the axis. Right-hand thread: A thread that when viewed axiay winds in a cockwise and receding direction. Threads are RH uness otherwise specified. Left-hand thread: A thread that when viewed axiay winds in a countercockwise and receding direction. A eft-hand threads are designated LH. Figure 1 2

4 Threaded Fasteners Lead: The distance a threaded part moves axiay with respect to a fixed mating part, in one compete revoution. Singe thread: A thread having the thread form produced on ony one heix of cyinder. On a singe thread, the ead and pitch are equivaent. Threads are aways singe uness otherwise specified (Fig. 2). Mutipe thread: A thread combination having the same form produced on two or more heices. For a mutipe thread, the ead is an integra mutipe of the pitch (e.g. on a doube thread, ead is twice the pitch). A mutipe thread permits a more rapid advance without a coarser (arger) thread form (Fig. 2). Figure 2 3

5 Screw Thread Profies h Profies of standard screw thread forms used in industry are shown in Fig. 3. Figure 3 4

6 Screw Thread Representation Externa (Fig. 4) and interna (Fig. 5) screw threads are iustrated beow. Thread notes are used in drawings in order to define type and size of screw threads. British Type UNC-2A-LH a b c d e a: Major diameter (inch) b: Threads per inch c: Form (i.e. Unified Nationa Coarse) d: Externa thread (B for interna) e: Left-hand thread (RH for right-hand) Metric Type M20 x 2 x y z x: Metric screw thread y: Major diameter (mm) z: Pitch (mm) Figure 4 Figure 5 5

7 Threads for Specific Purposes Screw threads for bind hoes with partiay tapped (Fig. 6) and bottom tapped (Fig. 7) are shown beow. The chamfered view of screw threads is drawn ony for arge chamfers (Fig. 8). There are aso threaded parts on pipes for specia appications (Fig. 9). Figure 8 Figure 6 Figure 9 Figure 7 6

8 Bots, Nuts and Studs Fig. 10 shows a nut (unfaced and faced at bottom side) and a bot having hexagona heads. There are five commony used type of fasteners in industry using bots, nuts, cap screws and studs (Fig. 11). In most cases, the combination of bot and nut, stud or cap screw with hexagona heads are used for hoding parts together. Nut Bot Figure 10 Figure 11 7

9 Assemby Drawings of Boted and Stud Joints h m n s H Dw R2 d d1 R A D r c 0 K d = major diameter d = 0.85d D = 2d H = 0.8d h = 0.7d = 2.2d A = 1.1d s = 0.15d c = s to 2s R = 1.5d r = based on R = 0.5c K = 3d = tabuated D R 2 w = 2d = 1.25d = = 1 1 to 2.5d + 0.5d + 0.4d m = tabuated Figure 12 Boted Joint n = tabuated Figure 13 Stud Joint m n H s Dw d d1 R A D r c 1 0 K 3 2 8

10 Various Types of Bots and Nuts Figure 14 Figure 15 9