JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year MACHINE DRAWING Previous Question Paper (August/September - 2022 - R16)

For a bolt of nominal diameter d = 20 mm, the standard proportions for hexagonal and square nuts are calculated as follows:

• Nominal diameter (d): 20 mm
• Width across flats (W): 1.5d + 3 mm = 33 mm
• Width across corners (W'): 2d = 40 mm
• Thickness of nut (H): 0.8d = 16 mm
• Chamfer radius (R): 1.5d = 30 mm

The three views required are the front view (elevation), top view (plan), and side view.

1. Front View: Draw a rectangle of width 33 mm and height 16 mm. For the hexagonal nut, show three faces with the central face width equal to 33/2 = 16.5 mm. Draw the chamfer curves on the top edges. For the square nut, show two faces with the central line indicating the junction.

2. Top View: For the hexagonal nut, draw a regular hexagon inscribed in a circle of diameter 40 mm (W'). For the square nut, draw a square of side 33 mm. Draw the inner circle representing the core diameter of the thread (approx. 0.85d = 17 mm) and the outer circle representing the nominal diameter (20 mm) with a 3/4 break for the thread clearance.

3. Side View: This view is identical to the front view for the hexagonal nut (showing three faces) and the square nut (showing two faces), positioned to the side of the elevation.

All views must be drawn using thin construction lines for the chamfer arcs and thick continuous lines for the visible outlines of the nut faces.

For a double strap, double riveted zig-zag butt joint with plate thickness (t) = 15 mm, the design parameters are calculated as follows:

The sectional front view shows the two main plates butted together with two cover straps placed on either side. The rivets pass through both straps and the main plates. In a zig-zag arrangement, the rivets in adjacent rows are staggered, so the sectional view must be taken through the zig-zag line to show the rivets in both rows. The top view displays the longitudinal edges of the plates, the edges of the cover straps, and the staggered positions of the rivet heads in the two rows on either side of the butt joint.

• Draw the center line of the butt joint and the main plates.
• Mark the rivet rows at distances of 0.8p to 0.9p from the joint.
• Place the rivets in a zig-zag pattern, ensuring the diagonal pitch is maintained.
• In the sectional view, show the main plates, the two cover straps, and the rivet shanks with snap heads.
• In the top view, represent the rivet heads as circles and indicate the plate and strap edges with hidden or visible lines as appropriate.