1. SCREWTHREADS MEM18003C
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2. SCREWTHREADS (VEE FORM)
Definition:
A screwthread is a helical structure used to convert between rotational and linear movement or force.
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3. SCREWTHREADS USES
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.
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4. SCREWTHREAD TERMINOLOGY
Pitch
Pitch is the distance, measured parallel to the axis, between corresponding points on adjacent thread forms.
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5. SCREWTHREAD TERMINOLOGY
Major
Diameter
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.
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6. SCREWTHREAD TERMINOLOGY
Pitch
Diameter
Pitch Diameter of a vee thread is the diameter at which the thickness of the tread is equal to half the pitch.
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7. SCREWTHREAD TERMINOLOGY
Minor
Diameter
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.
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8. SCREWTHREAD TERMINOLOGY
Crest
Crest of the thread is the prominent part of the thread, whether the thread is external or internal.
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9. SCREWTHREAD TERMINOLOGY
Angle
Angle of thread or Included Angle is the angle between flanks measured in the axial plane.
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10. SCREWTHREAD TERMINOLOGY
Root
Root of the thread is the bottom of the groove between adjacent flanks.
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11. SCREWTHREAD TERMINOLOGY
Flank
Flank or side of thread is the straight side which connects the crest and the root.
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12. SCREWTHREAD TERMINOLOGY
Depth
Depth of the thread is the Radial Distance between it’s crest and root.
Major Diameter – Minor Diameter 2
Depth of thread =
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13. SCREWTHREAD TERMINOLOGY
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.
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14. METRIC THREAD FORM To Calculate the Depth of Thread on a Bolt:
.591 x Pitch
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15. UNIFIED THREAD FORM To Calculate the Depth of Thread on a Bolt:
.613 x Pitch
Unified Thread Forms come in two series:
UNC Unified National Course
UNF Unified National Fine
NPT National Pipe Thread
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16. BRITISH STANDARD THREAD FORM
To Calculate the Depth of Thread on a Bolt:
.64 x Pitch
British Standard Thread Forms:
BSW British Standard Whitworth
BSF British Standard Fine
BSP British Standard Pipe
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17. IMPERIAL THREAD FORM To calculate the pitch of 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 1 8
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18. METHODS OF PRODUCING SCREW THREADS
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.
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19. HAND TAPPING PROCESS 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’
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20. CUTTING AN EXTERNAL THREAD With Hand Stock and Die
Two types of dies are:
Button Die
Used for manufacturing new threads.
Die Nut
Used for repairing or cleaning existing threads.
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21. EXAMPLES OF TAP WRENCHES AND STOCKS AND DIES
Set of Tap Wrenches
Tee-tap Wrench
Set of Taps and Dies
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22. Different types of fasteners that use Vee Threads
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