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SCREWTHREADS MEM18003C Fitting and Machining, Campbelltown College1.

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Presentation on theme: "SCREWTHREADS MEM18003C Fitting and Machining, Campbelltown College1."— Presentation transcript:

1 SCREWTHREADS MEM18003C Fitting and Machining, Campbelltown College1

2 2 Definition: A screwthread is a helical structure used to convert between rotational and linear movement or force. SCREWTHREADS (VEE FORM)

3 To fasten parts together, as with bolts and nuts, set screws, studs or pipe joints. To adjust the position of parts. To exert pressure, as with a vice, screw press or screw jack. Transmit motion. e.g. Lathe cross slide. Measuring device. e.g. micrometer. Fitting and Machining, Campbelltown College3 SCREWTHREADS USES

4 Fitting and Machining, Campbelltown College4 Pitch is the distance, measured parallel to the axis, between corresponding points on adjacent thread forms. Pitch SCREWTHREAD TERMINOLOGY

5 Fitting and Machining, Campbelltown College5 Major Diameter of a parallel tried is the diameter of a imaginary cylinder which just touches the crest of the external thread, and the root of an internal thread. The major diameter is the largest diameter of a screw or nut. Major Diameter SCREWTHREAD TERMINOLOGY

6 Fitting and Machining, Campbelltown College6 Pitch Diameter of a vee thread is the diameter at which the thickness of the tread is equal to half the pitch. Pitch Diameter SCREWTHREAD TERMINOLOGY

7 Fitting and Machining, Campbelltown College7 Minor Diameter of a parallel thread is the diameter of an imaginary cylinder which just touches the crest of an internal thread. The minor diameter is the smallest diameter of the thread on a screw or nut. Minor Diameter SCREWTHREAD TERMINOLOGY

8 Fitting and Machining, Campbelltown College8 Crest of the thread is the prominent part of the thread, whether the thread is external or internal. Crest SCREWTHREAD TERMINOLOGY

9 Fitting and Machining, Campbelltown College9 Angle of thread or Included Angle is the angle between flanks measured in the axial plane. Angle SCREWTHREAD TERMINOLOGY

10 Fitting and Machining, Campbelltown College10 Root of the thread is the bottom of the groove between adjacent flanks. Root SCREWTHREAD TERMINOLOGY

11 Fitting and Machining, Campbelltown College11 Flank or side of thread is the straight side which connects the crest and the root. Flank SCREWTHREAD TERMINOLOGY

12 Fitting and Machining, Campbelltown College12 Major Diameter – Minor Diameter 2 Depth of thread = SCREWTHREAD TERMINOLOGY Depth of the thread is the Radial Distance between it’s crest and root. Depth

13 Fitting and Machining, Campbelltown College13 Hand of thread:Will either be ‘Right’ or ‘Left’ hand. Right hand Thread – Nut turns in a clockwise direction. Left hand Thread – Nut turns in a anti clockwise direction. SCREWTHREAD TERMINOLOGY

14 Fitting and Machining, Campbelltown College14 To Calculate the Depth of Thread on a Bolt:.591 x Pitch METRIC THREAD FORM

15 Fitting and Machining, Campbelltown College15 To Calculate the Depth of Thread on a Bolt:.613 x Pitch Unified Thread Forms come in two series: UNCUnified National Course UNFUnified National Fine NPT National Pipe Thread UNIFIED THREAD FORM

16 Fitting and Machining, Campbelltown College16 To Calculate the Depth of Thread on a Bolt:.64 x Pitch British Standard Thread Forms: BSWBritish Standard Whitworth BSFBritish Standard Fine BSP British Standard Pipe BRITISH STANDARD THREAD FORM

17 Fitting and Machining, Campbelltown College17 To calculate the pitch of imperial threads: Imperial Threads = T.P.I = Threads Per Inch e.g. Pitch of an 8 T.P.I. Thread = Pitch =.125 Depth of Thread =.125 x.54 =.0675” 1 TPI 1818 IMPERIAL THREAD FORM

18 Fitting and Machining, Campbelltown College18 Screw threads may be formed by casting, rolling or metal removal process. The metal removal processes in common use are: Single point threading tool as used in the screw cutting lathe. Dies and chasers as used in die heads on capstan, turret and automatic lathes. Dies as used in hand stock and die. Hand taps and machine taps. A thread grinding process. Thread milling process. METHODS OF PRODUCING SCREW THREADS

19 Fitting and Machining, Campbelltown College19 Hand taps are for the cutting of female threads. Hand taps are made in sets of three and comprise of: Taper Intermediate Plug or ‘Bottoming’ HAND TAPPING PROCESS

20 CUTTING AN EXTERNAL THREAD With Hand Stock and Die Fitting and Machining, Campbelltown College20 Two types of dies are: Die Nut Used for repairing or cleaning existing threads. Button Die Used for manufacturing new threads.

21 Set of Tap Wrenches Set of Taps and Dies Fitting and Machining, Campbelltown College21 EXAMPLES OF TAP WRENCHES AND STOCKS AND DIES Tee-tap Wrench

22 22 Different types of fasteners that use Vee Threads Fitting and Machining, Campbelltown College


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