Jawaharlal Nehru Technological University Hyderabad B.Tech II Machine Drawing and Computer Aided Graphics Previous Question Paper (February - 2024 - R15)

To draw the Metric and Buttress thread profiles with a pitch (P) of 30 mm, follow these geometric constructions:

1. Metric Thread Profile (ISO Metric):

The metric thread has an included angle of 60°. The theoretical depth is 0.866P. For a pitch of 30 mm, the depth is 25.98 mm.

• Draw a horizontal baseline for the root.
• Mark the pitch distance of 30 mm.
• Construct an equilateral triangle with a height of 25.98 mm.
• Truncate the crest by 1/8th of the height (3.25 mm) and the root by 1/4th of the height (6.5 mm) to obtain the standard profile.

2. Buttress Thread Profile:

The buttress thread has one flank perpendicular to the axis and the other at an angle of 45°. The depth is 0.75P. For a pitch of 30 mm, the depth is 22.5 mm.

• Draw a horizontal line for the root.
• Mark the pitch of 30 mm.
• Draw a vertical line (90°) for the pressure flank.
• Draw a line at 45° to the vertical for the clearance flank.
• The crest and root are typically rounded or flat depending on the specific standard, with a height of 22.5 mm.

When drawing these, ensure the pitch is measured accurately along the pitch line, and use a scale that allows for clear representation of the thread angles and truncation depths.

For plates of thickness t = 10 mm, the design parameters for a double riveted zig-zag lap joint are calculated as follows:

• Diameter of rivet (d): Using Unwin's formula, d = 6.05 * sqrt(t) = 6.05 * sqrt(10) ≈ 19 mm. Standard practice adopts d = 20 mm.
• Pitch (p): For a zig-zag lap joint, p = 0.2 * (8d + t) ≈ 34 mm (minimum) or typically 3d to 4d, resulting in p ≈ 60-80 mm.
• Diagonal pitch (p_d): p_d = 0.6p + 0.4d ≈ 0.6(70) + 0.4(20) = 50 mm.
• Margin (m): m = 1.5d = 30 mm.
• Transverse pitch (p_t): p_t = 0.33p + 0.67d ≈ 37 mm (minimum) or typically 2d to 2.5d = 40-50 mm.

The sectional front view shows the two plates overlapping with two rows of rivets. The section plane passes through the zig-zag path, showing one rivet in full section and the other in the adjacent row. The view from above (top view) displays the plate edges, the two rows of rivet heads arranged in a zig-zag pattern, and the pitch distance between rivets in the same row.