Jawaharlal Nehru Technological University Hyderabad B.Tech II MACHINE DRAWING Previous Question Paper (December - 2018 - R13)

Conventional representations are standardized methods used in engineering drawings to simplify complex features while maintaining clarity. The representations for the requested features are as follows:

Radial Ribs: When ribs are arranged radially around a central axis, they are represented by drawing the rib profile in the view where it appears as a thin section. If the cutting plane passes through the ribs, they are typically not cross-hatched to avoid implying a solid mass, which helps distinguish the rib from the main body of the component.

Straight Knurling: This is represented by a series of parallel lines drawn at an angle of 45 degrees to the axis of the cylindrical part. The lines are spaced uniformly across the surface area designated for the knurled finish. A note is usually added to specify the pitch and type of knurl.

Diamond Knurling: This is represented by a cross-hatched pattern of lines inclined at 45 degrees to the axis of the part. The lines intersect to form a grid of diamond shapes covering the surface. Similar to straight knurling, the representation is simplified, and the specific knurling requirements are detailed in the accompanying technical notes or drawing specifications.

For a bolt with a nominal diameter (d) of 20 mm, the standard proportions for a hexagonal and square nut are based on d = 20 mm.

Key Proportions:

• 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 radius (R) = 1.5d = 30 mm

Views Required:

1. Front View (Elevation): A rectangle of size 33 mm x 16 mm. For the hexagonal nut, show three faces with the central face width as 16.5 mm. For the square nut, show one face of 33 mm width. Include the chamfer arc at the top.
2. Top View (Plan): For the hexagonal nut, draw a regular hexagon inscribed in a circle of diameter 40 mm. For the square nut, draw a square of side 33 mm. Both must show the inner circle representing the tapped hole diameter (approx. 17.3 mm for M20).
3. Side View: A rectangle of 33 mm x 16 mm showing the profile of the nut faces, with the chamfered edges represented by curves or straight lines depending on the orientation.

Draw the hexagonal nut with the width across flats parallel to the front plane to show three faces, and the square nut with two faces visible in the front view.