Question

Draw to scale 1:1, the front view and top view of a HEXAGONAL NUT of diameter 25 mm. Keep its axis vertical. Give standard dimensions. (8 marks)

Hint:

When drawing a nut or a bolt top view:
• An internal thread (inside a nut) has a complete circle on the inside and a 3/4 circle on the outside.
• An external thread (on a bolt) has a complete circle on the outside and a 3/4 circle on the inside.

Answer 1

Step 1: Calculating standard proportions of Hexagonal Nut ($d = 25\text{ mm}$):
Using the standard empirical formulas taught in Engineering Graphics:
• Nominal Diameter ($d$): $25\text{ mm}$
• Height or Thickness ($H$): $H = d = \mathbf{25\text{ mm}}$
• Width across flats ($W$): $W = 1.5d + 3\text{ mm} = 1.5 \times 25 + 3 = \mathbf{40.5\text{ mm}}$
• Width across corners ($D_{\text{corners}}$): $D_{\text{corners}} = 2d = \mathbf{50\text{ mm}}$
• Chamfer angle: $30^{\circ}$ to the top flat face of the nut.
• Radius of main chamfer arc ($R$): $R = 1.4d = 1.4 \times 25 = \mathbf{35\text{ mm}}$

Step 2: Step-by-Step Drafting of the Front View (Axis Vertical):
• Draw a vertical centerline.
• Draw a rectangle representing the outer boundary: width = $D_{\text{corners}} = 50\text{ mm}$ and height = $H = 25\text{ mm}$.
• Project the three visible faces of the hexagon from the top view:
• Middle face width = $d = 25\text{ mm}$ (centered).
• Two side faces width = $d/2 = 12.5\text{ mm}$ each.
• Draw the Chamfer Arcs:
• For the middle face: Draw a circular arc of radius $R = 35\text{ mm}$ touching the top edge of the nut, centered on the vertical axis.
• For the two side faces: Draw small chamfer arcs of radius $r$ (by construction, matching the height of the middle arc endpoints) to touch the top edge of the side faces.
• Draw the chamfer lines at $30^{\circ}$ from the top corners of the outer vertical lines down to the chamfer curve.
• Draw the inner threaded hole as hidden dashed lines: nominal diameter $d = 25\text{ mm}$ and minor/core diameter $d_c = 0.85d \approx 21.2\text{ mm}$.

Step 3: Step-by-Step Drafting of the Top View:
• Draw a vertical and a horizontal centerline intersecting at the center of your nut.
• Draw a circle of diameter equal to the width across flats ($W = 40.5\text{ mm}$).
• Construct a regular hexagon circumscribed about this circle:
• Draw two horizontal tangent lines at the top and bottom of the circle.
• Use a $30^{\circ}-60^{\circ}$ set-square to draw the remaining four slanted tangent sides of the hexagon.
• The circumscribing circle of diameter $40.5\text{ mm}$ represents the outer chamfer circle and is drawn as a full, thin circle.
• Draw the inner threaded hole:
• Draw a full, thick circle of diameter $d = 25\text{ mm}$ (representing the hole clearance).
• Draw a thin, $3/4$ (three-quarter) circle of core diameter $0.85d = 21.2\text{ mm}$ to represent the internal thread roots.