JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II MACHINE DRAWING Previous Question Paper (September/October - 2023 - R13)

The following five thread profiles are defined in terms of pitch (P):

1. ISO Metric Thread: Included angle is 60°. The depth is 0.613P. The crest is truncated by P/8 and the root by P/4.
2. British Standard Whitworth (BSW) Thread: Included angle is 55°. The depth is 0.64P. The crest and root are rounded with a radius of 0.137P.
3. Square Thread: Included angle is 0°. The depth is 0.5P. The width of the thread and the gap are both 0.5P.
4. Knuckle Thread: Included angle is 0°. The depth is 0.5P. Both the crest and root are semi-circular with a radius of 0.25P.
5. Acme Thread: Included angle is 29°. The depth is 0.5P + 0.01 inch (or 0.5P). The crest width is 0.3707P and the root width is 0.3707P.

For a hexagonal nut with a nominal diameter (d) of 20 mm, the standard proportions are as follows: width across flats (W) = 1.5d + 3 mm = 33 mm; thickness of nut (T) = 0.8d = 16 mm; radius of chamfer (R) = 1.5d = 30 mm.

The two views required are the front view (projected as a rectangle with chamfered edges) and the top view (a regular hexagon):

1. Front View: Draw a rectangle of 33 mm width and 16 mm height. The central hole has a diameter of 0.87d (approx 17.4 mm) representing the core diameter. The top face shows three visible faces of the hexagon, with the central face having a width of 0.5W (16.5 mm) and the two side faces having a width of 0.25W (8.25 mm). Draw the chamfer arcs using radius R = 30 mm centered on the vertical axis.
2. Top View: Draw a regular hexagon circumscribing a circle of diameter 33 mm. Draw an inner circle representing the core diameter of 17.4 mm. Draw a larger circle with a diameter of 33 mm representing the chamfered corners, which will be tangent to the sides of the hexagon.