CBSE Class 12 Engineering Drawing Worksheet Set 01

Question 1. (a) Construct an isometric scale.
Answer: Construction steps for an isometric scale:
1. Draw a horizontal baseline \(AB\). From point \(A\), draw two lines inclined at \(30^\circ\) and \(45^\circ\) to the baseline.
2. Mark true lengths (equal to actual measurements) on the \(45^\circ\) line at convenient intervals, such as 10 mm, 20 mm, 30 mm, etc.
3. From these division points on the \(45^\circ\) line, drop vertical perpendiculars down to intersect the \(30^\circ\) line.
4. The divisions marked along the \(30^\circ\) line represent the reduced isometric lengths in the ratio of \(\frac{\text{Isometric Length}}{\text{True Length}} = \frac{\cos 30^\circ}{\cos 45^\circ} \approx 0.816\).
5. Mark the zero point at the intersection and number the divisions accordingly to use as a working isometric scale.
In simple words: An isometric scale is a graphical converter used to measure and draw true lengths into reduced isometric lengths directly.
Exam Tip: Always construct the scale accurately using a protractor for \(30^\circ\) and \(45^\circ\) lines, and explicitly label both the true length scale and the isometric scale divisions.

Question 1. (b) Draw the isometric projection of the frustum of a triangular pyramid of base sides 40 mm, top sides 25 mm, 60 mm axis resting vertically on HP with a base side perpendicular to VP. Give all dimensions.
Answer: Construction steps for the isometric projection:
1. Draw the isometric axes originating from a common point with angles of \(30^\circ\) to the horizontal on both sides.
2. Draw the bottom equilateral triangular base of sides 40 mm in isometric view, keeping one base side perpendicular to the vertical plane orientation.
3. Locate the center of the bottom triangle and erect a vertical axis line of height 60 mm to find the center of the top base.
4. Draw the top equilateral triangular base of sides 25 mm parallel to the bottom base, properly offset corresponding to the axis center.
5. Connect the corresponding corners of the top and bottom equilateral triangles to complete the lateral edges of the frustum.
6. Darken all visible outlines, remove or lighten construction lines, and mark the dimensions (base side 40 mm, top side 25 mm, and axis height 60 mm) using standard dimensioning lines.
In simple words: Draw a bottom triangle and a smaller top triangle directly above it along a 60 mm vertical axis, then join their corners.

Exam Tip: Remember that isometric projections use true measurements taken from an isometric scale, whereas isometric drawings use true scale measurements directly.

Question 1. (c) A cylindrical disc of base diameter 90 mm & height 50 mm rests on its circular base on HP. A regular pentagonal prism of base sides 26 mm & length 50 mm with its axis perpendicular to VP rests on one of its rectangular faces, over the top circular face of the disc. Draw the isometric projection of the combination.
Answer: Construction steps for the combination of solids:
1. Draw the isometric view of the cylindrical disc of base diameter 90 mm and height 50 mm resting on HP by enclosing its circular base in an isometric rhombus of \(90 \text{ mm} \times 90 \text{ mm}\) and drawing the top and bottom elliptic contours.
2. Locate the geometric center of the top circular face of the disc.
3. Construct the regular pentagonal prism of base side 26 mm and length 50 mm such that its axis is oriented perpendicular to the VP (parallel to the length axis in isometric view) and it rests stably on one of its rectangular faces directly centered on top of the disc.
4. Draw all visible outlines of both the cylindrical disc and the resting pentagonal prism, eliminating hidden lines that fall inside solid intersections.
5. Dimension the assembly clearly, indicating the disc diameter (90 mm), disc height (50 mm), pentagonal base side (26 mm), and prism length (50 mm).
In simple words: Draw a cylinder as the base, find its top center, and draw a pentagonal prism resting on its side over the top surface.

Exam Tip: Constructing isometric ellipses for circular bases requires plotting four-center arcs accurately inside an isometric rhombus.

Question 2. (a) Draw to scale 1:1 the front view & top view of a T-headed bolt of size M 30 keeping its axis vertical.
Answer: Standard empirical proportions for a T-headed bolt of nominal diameter \(d = 30 \text{ mm}\):
- Nominal diameter (\(d\)) = 30 mm
- Thread length = Standard length as per application
- Head length = \(0.75d = 0.75 \times 30 = 22.5 \text{ mm}\)
- Head width = \(1.5d = 1.5 \times 30 = 45 \text{ mm}\)
- Head thickness = \(0.75d = 22.5 \text{ mm}\)
Front View Construction:
1. Draw the vertical centerline representing the axis of the bolt.
2. Draw the threaded shank of diameter 30 mm extending downwards with standard thread conventions (thin continuous core line).
3. Draw the T-head at the top with a width of 45 mm and a thickness of 22.5 mm, incorporating standard chamfers or rounding where applicable.
Top View Construction:
1. Directly below or above the front view, draw concentric circles representing the shank diameter (30 mm) and the projecting rectangular or square T-head dimensions.
2. Add standard hatching and dimensioning labels indicating size M 30.
In simple words: Draw a bolt with a T-shaped head at the top and a vertical threaded cylinder body, showing both front and top views to full size (1:1 scale).

Exam Tip: For metric designation M 30, always use nominal diameter \(d = 30 \text{ mm}\) as the base for calculating all standard head proportions.

Question 2. (b) Sketch freehand the front view & top view of a counter sunk head rivet of diameter 30 mm keeping its axis vertical.
Answer: Standard empirical proportions for a countersunk head rivet of diameter \(d = 30 \text{ mm}\):
- Shank diameter (\(d\)) = 30 mm
- Head diameter (\(D\)) = \(2d = 2 \times 30 = 60 \text{ mm}\)
- Head height / depth (\(h\)) = \(0.5d = 0.5 \times 30 = 15 \text{ mm}\)
- Countersunk angle = \(60^\circ\) or \(90^\circ\) (standard \(90^\circ\) included angle is commonly used)
Front View Construction:
1. Draw a vertical centerline.
2. Draw the cylindrical shank of diameter 30 mm with a break line at the lower end indicating partial length.

3. Draw the countersunk head at the top with a top diameter of 60 mm tapering down to the shank diameter at an included angle of \(90^\circ\), having a vertical head height of 15 mm.
Top View Construction:
1. Draw two concentric circles: an outer circle of diameter 60 mm representing the top edge of the countersunk head, and an inner hidden or visible circle of diameter 30 mm representing the shank.
In simple words: Sketch a rivet with a conical flush head at the top and a straight cylindrical pin extending downwards.

Exam Tip: Freehand sketches must be neat, proportioned correctly relative to diameter \(d\), and drawn with smooth continuous lines without using drafting instruments.

Question 3. (a) fig shows the details of the parts of Gib and Cotter Joint. Assemble these parts correctly and draw to full size scale the following views: (i) Front view, upper half in section (ii) Top view. Write heading & scale used. Draw projection symbol. Give eight important dimensions.
Answer: Assembly procedure and details for the Gib and Cotter Joint:
1. Align the socket end and strap end rods coaxially along the horizontal centerline.
2. Insert the gib and cotter wedge assembly through the slotted rectangular cotter holes to tightly lock the socket and strap together.
3. Front View (Upper Half in Section): Draw the fully assembled joint with the upper half sectioned using standard section lines (\(45^\circ\) hatching) to show internal contact surfaces between the strap, socket, gib, and cotter.
4. Top View: Draw the complete external top view projecting directly from the front view, showing overall widths and taper profiles.
5. Include the heading "GIB AND COTTER JOINT - ASSEMBLED", state scale 1:1, draw the standard third-angle or first-angle projection symbol, and mark eight essential dimensions (such as nominal rod diameter, total joint length, strap width, cotter taper dimensions, and clearance gaps).
In simple words: Assemble the rod ends, gib, and cotter together, then draw the cut front view and top view with proper hatching and dimensions.

Exam Tip: Ensure that section hatching lines do not cross solid outlines and that hatching spacing is uniform throughout all component parts in the sectional view.