Question 2 of 3: Auxiliary view, isometric view and dimensioning of a bearing bracket

Question 2: Auxiliary view, isometric view and dimensioning of a bearing bracket (30 marks)

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.

Reading the views. Once the page is rotated to landscape, the three views align by projection (top above front, right side to the right of front). The part is a single-piece bearing bracket with four features:

• Base plate. A thin plate (proportions about 120 × 40 × 10) whose two front corners are rounded. The rounded corners show as arcs in the top view and as tangent lines near each end in the front and side views.
• Boss. A cylindrical boss with a through bore lies above the left end of the base, with its axis running front to back. The front view shows it as two concentric circles, and it is about 40 in diameter with a 20 bore, centred about 50 above the bottom. The boss is flush with the base at the back and overhangs the front of the base by about 10; the top and side views show this.
• Web. A web fills the back half of the base depth (about 20 thick). Its left face is vertical and tangent to the boss. Its sloping face runs from a tangent point on the top of the boss down to the top-right corner of the base, at about 32.5° to the horizontal.
• Two blind holes (about Ø8, 10 deep) are drilled perpendicular to the sloping face, spaced symmetrically about its midpoint and centred on the web thickness. The front view shows them as small dashed rectangles perpendicular to the slope, which confirms that the slope is seen as an edge in that view. The top and side views show them as ellipses, each with a hidden ellipse for the hole bottom.

a) Auxiliary view

The sloping face is an inclined surface, perpendicular to the frontal plane, so it appears as an edge (the sloping line) in the front view. A primary auxiliary view projected from the front view shows it in true size:

1. Draw the fold line parallel to the sloping edge, a short distance above it.
2. Draw projectors from the ends of the sloping edge, both hole centres and the boss, perpendicular to the fold line.
3. Transfer depths (the front-to-back dimension) from the top or right-side view, measuring from the corresponding fold line in each view. The front of the part is nearest the fold line.
4. Draw the sloping face as its true rectangle (true length × web thickness) with the two holes as true circles at their true spacing. As a partial auxiliary view, add only the part of the boss that is needed to locate the face; its bore shows as hidden lines, because the bore's axis lies parallel to the auxiliary plane. The base is left out, as is normal practice for a partial auxiliary view.

b) Isometric view

Box in the overall size, then build the part in this order:

1. Draw the base, rounding the two front corners with isometric (four-centre) ellipse arcs.
2. Draw the boss as two isometric ellipses in the frontal plane, 50 apart along the depth axis, joined by tangent lines, with the bore ellipse on the front face.
3. Draw the web's front face in the back half of the base: a vertical left edge under the boss, and the sloping edge from the tangent point down to the base corner. Carry that edge back through the web thickness to form the sloping face.
4. Plot the two blind holes on the sloping face point by point, because that face is not an isometric plane. They appear as small ellipses whose long axis runs across the face.

c) Full dimensioning (values shown as "xx")

Following ASME Y14.5 practice (CSA B78.2 in Canada), each dimension goes on the view where its feature appears in true shape, and each size is stated once:

• Front view. The base length and thickness. The boss centre height from the bottom (the mounting face) and its horizontal position from the left end. The boss outside diameter and the bore diameter, as Øxx callouts on leaders to the circles, with the bore marked THRU. The sloping face carries a TANGENT note instead of an angle: its position is already fixed by tangency to the boss and by ending at the base corner, so an angle would be a redundant, conflicting dimension.
• Top view. Depths measured from the back face, which is a common baseline: the base depth, the web thickness and the boss length. The front corner radius as 2X R xx.
• Auxiliary view. Only here do the web holes appear in true size and position. Give the hole callout as 2X Øxx with a depth of xx. Locate the holes from the lower end of the sloping face (a real edge), with a baseline dimension to the nearer hole and the hole-to-hole spacing, and locate them across the face from the back face.

Nothing is dimensioned twice, no dimension points to a hidden line, and the right-side view needs no dimensions because every feature is already fixed.