JNTU B.Tech II MACHINE DRAWING Previous Question Paper (May - 2019 - R16)

For a double-riveted, double-cover butt joint with zig-zag riveting and a plate thickness (t) of 15 mm, the design parameters are calculated as follows:

1. Diameter of rivet (d): Using Unwin's formula, d = 6.04 * sqrt(t) = 6.04 * sqrt(15) ≈ 23.4 mm. Standard practice adopts d = 24 mm.

2. Thickness of cover plates (t1): t1 = 0.625 * t = 0.625 * 15 ≈ 9.5 mm (use 10 mm).

3. Pitch (p): For zig-zag riveting, p = 0.33 * d + 2 * d + 0.67 * d (approx) or typically p = 3 * d to 4 * d. Using p = 3.5 * d = 84 mm.

4. Transverse pitch (pt): For zig-zag, pt = 0.6 * p = 50 mm.

5. Margin (m): m = 1.5 * d = 36 mm.

The sectional front view shows the two main plates butting against each other, sandwiched between two cover plates. The rivets pass through all four plates. In a zig-zag arrangement, the rivets in adjacent rows are staggered, so the section line must be stepped to pass through the center of the rivets. The top view shows the pitch distance along the rows and the staggered (zig-zag) positioning of the rivet heads, with the margin and transverse pitch clearly marked.

Conventional representations of thread forms are standardized in engineering drawing to simplify the depiction of complex helical shapes. The following four common thread forms are represented by their profile shapes:

1. ISO Metric Thread: Represented by a triangular profile with an included angle of 60°. The crests are flat, and the roots are rounded.
2. Whitworth (BSW) Thread: Represented by a triangular profile with an included angle of 55°. Both the crests and roots are rounded.
3. Square Thread: Represented by a square profile where the depth and width of the thread are equal to half the pitch. The sides are perpendicular to the axis.
4. Acme Thread: Represented by a trapezoidal profile with an included angle of 29°. It is used for power transmission where a stronger thread than the square form is required.

In technical drawings, these are typically simplified using two parallel lines representing the major and minor diameters, with the thread profile indicated in a sectional view or a detailed callout.