A Text Book on Engineering Graphics - Central Board of Secondary ...
A Text Book on Engineering Graphics - Central Board of Secondary ...
A Text Book on Engineering Graphics - Central Board of Secondary ...
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MACHINE DRAWING<br />
2.4.2 METRIC THREAD<br />
The Bureau <strong>of</strong> Indian standards (BIS) has recommended the adopti<strong>on</strong> <strong>of</strong> ISO (INTERNATIONAL<br />
ORGANISATION FOR STANDARDISATION) pr<strong>of</strong>ile with the metric screw thread system. In metric<br />
thread, the external and internal thread vary in shape. It can also be called as unified thread. In<br />
general, this ISO-metric thread will be specified using the basic designati<strong>on</strong>. The basic<br />
designati<strong>on</strong> c<strong>on</strong>sist <strong>of</strong> the letter M followed by the nominal size (major diameter in mm) and<br />
followed by the pitch in mm.<br />
For example<br />
M20 x 1.5 means the major diameter <strong>of</strong> the metric thread is 20mm and the pitch is 1.5mm. Let us<br />
now draw the standard pr<strong>of</strong>iles <strong>of</strong> metric screw thread<br />
Example 2:<br />
D = 0.866 P<br />
D<br />
8<br />
Draw to scale 1:1, the standard pr<strong>of</strong>ile <strong>of</strong> metric screw thread (external) taking<br />
enlarged pitch as 50mm. Give standard dimensi<strong>on</strong>s.<br />
d = 0.61 P<br />
D<br />
6<br />
P 0.5 P<br />
P<br />
50<br />
0.86P<br />
43<br />
EXTERNAL THREAD<br />
0.61P<br />
30.5<br />
METRIC SCREW THREAD PROFILE<br />
Fig 2.6<br />
ENGINEERING GRAPHICS 47<br />
60º<br />
D/8<br />
6.3<br />
D/6<br />
8.3
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