JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II MACHINE DRAWING Previous Question Paper (December - 2018 - R15)

In engineering drawing, conventional representations are used to simplify complex features. The representations for the requested elements are as follows:

Radial Ribs: When ribs are arranged radially around a central axis, they are represented by drawing the rib profile in the sectional view. If the cutting plane passes through the ribs, they are generally not cross-hatched even if the section plane cuts them, to avoid giving a false impression of solidity. They are drawn using thin continuous lines to indicate their extent.

Straight Knurling: This is represented by a series of parallel lines drawn at an angle of 30 degrees to the axis of the cylindrical component. These lines cover the surface area designated for the knurl, indicating the straight-cut pattern used for providing a better grip.

Diamond Knurling: This is represented by a cross-hatched pattern of lines inclined at 30 degrees to the axis of the component, intersecting each other to form a diamond-shaped grid. The lines are drawn as thin continuous lines over the specified surface area to denote the standard diamond knurling pattern.

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

Proportions:

• Nominal diameter (d) = 20 mm
• Width across flats (W) = 1.5d + 3 mm = 33 mm
• Width across corners (D) = 2d = 40 mm
• Thickness of nut (T) = 0.8d = 16 mm
• Chamfer angle = 30 degrees

Drawing Procedure:

1. Front View: Draw a rectangle of size 33 mm x 16 mm. Mark the chamfer arc on the top face using a radius of 1.5d (30 mm) for the central face and smaller radii for the side faces.
2. Top View: For the hexagonal nut, draw a circle of diameter 33 mm (inscribed) and circumscribe a regular hexagon. For the square nut, draw a square of side 33 mm. Draw the chamfered edges as concentric circles or arcs representing the intersection of the cone with the faces.
3. Side View: Draw the side profile showing the thickness of 16 mm and the projected edges of the chamfered faces.

The hexagonal nut top view shows six faces, while the square nut top view shows four faces. Ensure the central hole for the 20 mm bolt is represented by a circle of diameter 0.85d (approx. 17 mm) in the top view and hidden lines in the front and side views.