04-BS-15 · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams, 04-BS-15 Engineering Graphics & Design Process, 2018-May. Closed-book, no calculator; five questions constitute a complete exam paper, and all sketches must be freehand (no straightedges).
Reference texts: Bertoline & Wiebe, Technical Graphics Communication (4th ed.) — orthographic projection, isometric pictorials, auxiliary and section views, first/third-angle projection, dimensioning; Giesecke et al., Technical Drawing / Engineering Graphics (15th ed.) — ASME Y14.5 / CSA B78.1 dimensioning and tolerancing, ISO fit systems, constructive solid geometry (Boolean primitives); Ulrich & Eppinger, Product Design and Development — Quality Function Deployment / House of Quality.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
[Figure not reproduced: source figure. See the official exam paper or the cited reference text.]
Reading the pictorials. The two pictorials show one part from opposite corners. It has a rectangular base plate with a counterbored hole at each corner. On the plate stands a vertical web whose straight sides are tangent to a horizontal cylindrical boss, so the web's end face has a “tombstone” outline (a rectangle capped by a semicircle). A through bore runs along the boss axis. The boss is longer than the web is thick: it is flush with the web on the front face (left pictorial) and stands proud of the web on the back face (right pictorial, where the annular end face sits in front of the plain web face). The front face of the web carries a blind rectangular pocket below the boss; the pocket's roof is the underside of the boss, which is why its top edge is curved. Small fillets run along the web-to-plate junction. There is no window through the web, because the back face in the right pictorial is plain.
Assumption (per exam Note 1). No sizes are printed, so the views are drawn to proportions read off the pictorials: plate about 140 × 90 × 14, boss Ø60 × 42 long on a Ø28 bore with its axis 72 above the plate, web 25 thick, pocket 36 wide × 12 deep, holes Ø10 with Ø18 counterbores. They set the drawing scale only; every size is “xx” in part b).
Choice of views. The Front view looks along the bore axis at the pocketed face. It shows the most characteristic shape (the tombstone web, the bore as a true circle and the pocket opening) with the fewest hidden lines. In third-angle projection the Top view goes directly above the Front view and the Right-side view directly to its right, both aligned with it by projectors. Three views are needed: the plate thickness, web thickness, boss length and pocket depth appear only in the top and side views.
Front view. The plate is a low rectangle. Each counterbored hole appears as hidden lines: a narrow pair for the hole and a wider, shallower pair for the counterbore, joined by the hidden counterbore floor. The front and back holes of each side project onto the same lines. The web's sides rise straight from the plate, with small fillet arcs at their feet, and blend tangentially into the R30 boss arc. The bore is a visible true circle. The pocket shows as two vertical edges running from the plate up to the boss, closed at the top by an arc of the boss circle.
Top view. The plate footprint carries the four counterbored holes as pairs of concentric circles. The boss is seen as a rectangle whose width is its diameter and whose depth is its length. The web lies directly under the boss and has the same width, so it adds no visible line. Hidden lines show the bore along the full boss length and the pocket just behind the front face: two short side walls and its back wall.
Right-side view. The front faces of web and boss are coplanar, giving one vertical edge from the plate to the top of the boss. The boss is a rectangle that projects beyond the web's back face, and that back face drops as a vertical edge to the plate. Hidden lines show the bore, the pocket (its back wall, and its roof line where the pocket side wall meets the boss) and the counterbored holes.
Dimensioning follows ASME Y14.5 / CSA B78.1 practice. Extension lines start with a small gap from the outline, dimension lines end in arrowheads, and each feature is dimensioned once, in the view that shows it in true shape and, where possible, to visible lines. Front view: plate length, plate thickness, hole spacing along the length, height of the bore axis above the plate underside, boss radius (R xx; it also fixes the web width, because the sides are tangent), bore diameter (Øxx THRU), pocket width and the fillet radius (R xx TYP). Top view: plate width, hole spacing across the width, and the hole callout “4X Øxx THRU, C'BORE Øxx, xx DEEP” (drawn with the counterbore and depth symbols on a real drawing). Right-side view: boss length and its position from the front edge of the plate, web thickness and pocket depth. Pocket depth is the one dimension that must go to a hidden line, which is acceptable when no view shows the feature visibly. The part is symmetric about its centre plane, so the boss is located by the centreline and needs no separate dimension.
(1) Base: sketch the plate rectangle on the top (XY) plane, symmetric about the origin, and extrude it to the plate thickness. (2) Web: on a plane parallel to the front plane, sketch the tombstone profile: two vertical lines from the plate top, tangent to a semicircle centred on the bore axis. Extrude it rearward by the web thickness and merge. (3) Pocket: on the web's front face, sketch a rectangle of the pocket width from the plate top up to the bore-axis height, and extrude-cut it to the pocket depth. (4) Boss: on the same front face, sketch the boss circle concentric with the web arc and extrude it rearward by the boss length. It is flush at the front and proud at the back, and because it is added after the pocket cut it refills the top of the pocket, so the pocket roof becomes the boss surface exactly as the pictorial shows. (Cutting the pocket “up to surface” after the boss gives the same result.) (5) Holes: put a Ø28 hole through all, concentric with the boss. Then use a counterbored hole feature (hole wizard) on the plate top at four sketch points, or one hole plus a rectangular pattern. (6) Fillets: fillet the web-to-plate edges last, so that they act on the finished solid. All sizes are driven by sketch dimensions and relations (the tangency and concentricity constraints), so changing, say, the boss diameter automatically updates the web width, the pocket roof and the bore position.
Production quantity drives the method. For more than a few parts, the natural route is casting (sand-cast grey or ductile iron, or aluminium; die or investment casting at high volume) followed by machining the functional surfaces. The fillets, tangent web and pocket are all casting-friendly. For one-offs or small batches the part can be CNC-milled from solid plate or block. A 3-axis mill produces every feature, but most of the stock is removed as chips, and the pocket's inside corners take the end-mill radius. A third option is a weldment: flame-cut plate for the base and web, with a thick-walled tube for the boss, welded and then machined. It is cheap to make, but the welds distort the part and change the look of the design.
Casting issues. The mould should draw along the bore axis. In that direction the tombstone profile, the pocket (open toward the front) and the proud boss (open toward the back) all withdraw without side cores. The bore can be cored or simply drilled, and the counterbored holes are drilled afterwards because their axes are at right angles to the draw. Faces parallel to the draw need 1–2° of draft. The pattern is made oversize to allow for shrinkage, with machining allowance on the base face and bore. Sections are reasonably uniform (plate 14, web 25, boss wall 16), and the pocket usefully removes metal from the thickest junction below the boss, where a hot spot would otherwise risk shrinkage porosity.
Machining issues. The base underside is milled flat first and becomes the datum. The bore is then bored or reamed to size (typically H7 if it carries a shaft or bushing) in a set-up located from that face, so that the bore axis stays parallel to the base at the specified height. If the base and bore are machined in unrelated set-ups, that relationship cannot be held. The four holes are drilled and counterbored from the same datum so that their pattern matches the mating part.
