Jawaharlal Nehru Technological University Hyderabad B.Tech III MACHINE DRAWING AND COMPUTER AIDED GRAPHICS Previous Question Paper (March - 2021 - R18)

For a hexagonal nut on a M24 bolt, the standard dimensions are calculated based on the nominal diameter (D = 24 mm):

• Width across flats (W) = 1.5D + 3 mm = 39 mm.
• Thickness of nut (T) = 0.8D = 19.2 mm (approx. 20 mm).
• Chamfer radius (R) = 1.5D = 36 mm.
• Nominal diameter of bolt (D) = 24 mm.

The three views required are:

1. Front View: Shows the thickness of the nut with three faces visible. The top face is chamfered, represented by a circular arc of radius R.
2. Top View: A regular hexagon inscribed in a circle of diameter W (39 mm), with the inner hole representing the tapped thread diameter.
3. Side View: Shows the profile of the nut, typically represented as a rectangle with the chamfered edges visible.

Conventional representation of screw threads involves drawing two parallel lines for the major diameter (continuous thick line) and the minor diameter (continuous thin line). For sectioned views, the threads are shown with a specific profile.

(i) BSW Thread (Pitch = 50 mm): The BSW thread has a 55-degree included angle. In section, draw the V-profile with rounded roots and crests. The pitch of 50 mm is measured from crest to crest.

(ii) Acme Thread (Pitch = 60 mm): The Acme thread has a 29-degree included angle. In section, draw the trapezoidal profile with flat crests and roots. The pitch of 60 mm is the distance between corresponding points on adjacent threads.

For both, ensure at least three full thread profiles are visible in the sectional view, clearly showing the difference between the 55-degree V-shape for BSW and the 29-degree trapezoidal shape for Acme threads.