BT-105 Engineering Graphics - Jun 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aWhat is scale? Classify its different types. What are the main uses of scale?
   How to answer

   • Definition of engineering scale and Representative Fraction (R.F.)
   • Classification: Full size, reducing, and enlarging scales
   • Types based on construction: Plain scale, Diagonal scale, Vernier scale, Comparative scale, Scale of chords
   • Key uses in technical drawing and mapping
2. 7 Marks
   bConstruct a vernier scale to read meters, decimeters and long enough to measure up to 6 meters when 1 meter is represented by 2.5 centimeters. Find R.F. and show on it a distance of 4.33 meters.
   How to answer

   • Calculate R.F. = 2.5 cm / 100 cm = 1/40
   • Calculate Length of Scale (LOS) = (1/40) * 600 cm = 15 cm
   • Divide 15 cm line into 6 equal parts (each representing 1 meter)
   • Subdivide main scale into decimeters and construct vernier scale to read down to hundredths of a meter (0.01 m or centimeters)
   • Mark the distance of 4.33 m clearly with dimension lines
3. 7 Marks
   aWhat is 3D modeling? Explain types of modeling.
   How to answer

   • Definition of 3D modeling in CAD/engineering graphics
   • Wireframe Modeling: characteristics, advantages, limitations
   • Surface Modeling: characteristics, representation of complex contours
   • Solid Modeling: constructive solid geometry (CSG), boundary representation (B-Rep), parametric modeling
4. 7 Marks
   bConstruct a parabola when the distance between focus from the directrix is equal to 60 mm. Draw a tangent and normal at any point on the parabola.
   How to answer

   • Draw directrix AB and axis perpendicular to it, locating focus F at 60 mm from directrix
   • Locate vertex V at midpoint of directrix-focus line (30 mm from directrix, since e = 1)
   • Select points along axis, draw perpendicular ordinates, and using arcs from focus F locate parabola points
   • Join points to form a smooth parabolic curve
   • Select arbitrary point P on curve, connect to F, draw perpendicular to PF intersecting directrix at T, join TP for tangent and draw normal perpendicular to TP
5. 7 Marks
   aA straight line segment is 100 mm long, measures 80 mm in plan and 70 mm in elevation. The middle point M is situated 36 mm above H.P. and 46 mm in front of V.P. Draw the top and front views of the line AB.
   How to answer

   • Draw reference line XY and plot projections of midpoint M (m' at 36 mm above XY, m at 46 mm below XY)
   • Determine inclinations $\theta$ and $\phi$ using relations $\cos\theta = 80/100 = 0.8$ and $\cos\phi = 70/100 = 0.7$
   • Determine vertical difference in height between ends $\Delta h = \sqrt{100^2 - 80^2} = 60$ mm and horizontal difference in depth $\Delta d = \sqrt{100^2 - 70^2} = \sqrt{5100} \approx 71.4$ mm
   • Set locus lines for end points equidistant from midpoint projections (above and below)
   • Draw front view a'b' = 70 mm passing through m' and top view ab = 80 mm passing through m
6. 7 Marks
   bName the methods which are employed to determine the length and true inclinations of a straight line.
   How to answer

   • Rotating Line Method (or Revolution Method)
   • Rotating Trapezoid / Trapezium Method
   • Auxiliary Plane Method (Auxiliary Front/Top Plane Method)
   • Brief explanation of the principle of each method
7. 7 Marks
   aA rectangular plate ABCD measuring $45\text{ mm} \times 35\text{ mm}$, has its diagonal AC inclined at $30^\circ$ to the H.P. where as the diagonal BD makes an apparent angle of $45^\circ$ to V.P. Draw its projection.
   How to answer

   • Stage 1: Assume plate resting with diagonal AC in HP, draw true shape in top view ($45\text{ mm} \times 35\text{ mm}$) and front view on XY line
   • Stage 2: Tilt front view so that diagonal AC is inclined at $30^\circ$ to XY; project downward to obtain reduced top view
   • Stage 3: Rotate the second top view so that diagonal BD makes an apparent angle of $45^\circ$ with XY (V.P.)
   • Project upward from top view and horizontally from second front view to obtain final front view
8. 7 Marks
   bDraw the projections of a pentagonal plane, side 25 mm, resting in the H.P. on one of its edges. The plane of pentagon is inclined at $45^\circ$ to the H.P. and the perpendicular, from the midpoint of the resting edge, makes an angle of $30^\circ$ with the V.P.
   How to answer

   • Stage 1: Draw true shape pentagon in top view with one edge perpendicular to XY (resting edge), front view on XY line
   • Stage 2: Tilt front view at $45^\circ$ to XY line with resting edge on XY, project downwards to obtain intermediate top view
   • Stage 3: Measure apparent length of the median from the midpoint of the resting edge, and orient this median at $30^\circ$ to XY (since it's the projection line of the perpendicular)
   • Project upwards and across from intermediate views to obtain final front view
9. 14 Marks
   A regular tetrahedron edge of base 30 mm, is resting on one of its edges on the horizontal plane. The resting edge makes an angle of $45^\circ$ to V.P. and the face containing the edge makes an angle of $30^\circ$ to H.P. Draw its projections.
   How to answer

   • Calculate height of regular tetrahedron: $H = \sqrt{\frac{2}{3}} s = \sqrt{\frac{2}{3}} \times 30 \approx 24.5$ mm
   • Stage 1: Position tetrahedron resting on a triangular face on HP such that one edge is perpendicular to VP, draw TV and FV
   • Stage 2: Tilt the solid so that the face containing the resting edge makes $30^\circ$ with HP, project intermediate TV
   • Stage 3: Rotate the resting edge in TV to make $45^\circ$ with XY line (V.P.)
   • Project to draw final front view showing visible and hidden edges
10. 14 Marks
    A right circular cylinder, base $\phi 54$ and axis 75 mm long, with a circular hole of $\phi 30\text{ mm}$, drilled centrally through it, rests on its base on H.P. A section plane $45^\circ$ to H.P. cuts the axis at a distance of 20 mm from the top end face. Draw the sectional top view and true shape of section.
    How to answer

    • Draw front view and top view of hollow cylinder (outer dia 54 mm, inner hole dia 30 mm, height 75 mm)
    • Locate cutting plane in FV inclined at $45^\circ$ to XY, passing through axis at 20 mm below top face
    • Determine cut points on outer generators and inner hole generators
    • Project cut points to TV to construct sectional top view and apply hatching at $45^\circ$
    • Draw auxiliary plane parallel to cutting plane line and project true shape consisting of two concentric ellipses (outer and inner cut shapes)
11. 7 Marks
    aA square prism of 50 mm edge and 65 mm height stands on one of its faces on the H.P. with a vertical face making $45^\circ$ angle with V.P. A horizontal hole of 25 mm diameter is drilled centrally through the prism such that the hole passes through the opposite vertical edges of the cube. Draw the development of the surface of the prism and the hole.
    How to answer

    • Draw TV of prism as square with edges at $45^\circ$ to XY, and FV as rectangle 65 mm high
    • Draw circle of $\phi 25$ mm centrally in front view/side view as required representing horizontal hole
    • Divide hole perimeter into 12 equal parts and project intersection points onto prism vertical faces and edges
    • Unroll prism lateral surface into a rectangle of length $4 \times 50 = 200$ mm and height 65 mm
    • Transfer coordinates of hole boundary points onto development to draw smooth penetration cutouts
12. 7 Marks
    bA cube of 40 mm side rests centrally on a square block of 60 mm edges and 20 mm thick. Draw the isometric projection of the two objects with the edges of the two blocks mutually parallel to each other.
    How to answer

    • Construct isometric scale (ratio $\sqrt{2}/\sqrt{3} \approx 0.816$)
    • Draw isometric axes at $30^\circ$ to horizontal
    • Draw the bottom square block ($60 \times 60 \times 20$ mm isometric dimensions)
    • Locate center of top face of square block and lay out the base of the cube (40 mm isometric edges, centrally placed and edges parallel to slab)
    • Construct cube of height 40 mm isometric and darken all visible edges, omitting hidden lines
13. 14 Marks
    Write short notes on the following (any two) i) Editing commands in CAD ii) Layering concept iii) Purpose of Zoom command
    How to answer

    • Editing commands in CAD: Move, Copy, Trim, Extend, Offset, Mirror, Fillet, Rotate with usage and syntax
    • Layering concept: Organization of drawing elements, assigning color, linetype, lineweight, freeze/thaw, lock/unlock, visibility control
    • Purpose of Zoom command: Magnifying/demagnifying display, Zoom All, Zoom Window, Zoom Extents, Zoom Realtime, navigation without altering actual scale/geometry