View selection and hidden-line clutter on a bracket drawing
A mounting bracket is 80 mm wide, 50 mm deep and has a 12 mm thick base. A vertical web, 12 mm thick, rises 60 mm from the base; its top face is inclined at 30° to the horizontal, dropping toward the front. A Ø16 mm hole passes horizontally through the web, its centre 25 mm above the base and 20 mm from the left edge. A Ø10 mm hole passes vertically through the base, 15 mm from the left edge and 20 mm from the front edge. The candidate has drawn a front view and a top view in first-angle projection and has included every hidden line. The sheet is crowded, a Ø16 circle is broken by hidden lines, and the left-hand end of the inclined face has no centre line. The candidate asks whether a section would be better and which views are really necessary.
1. Recommend the minimum set of views and/or sections needed to define the bracket clearly, and justify each view by the feature it controls.
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The front view should be the main view looking at the web face. It shows the 30° inclined top, the web height of 60 mm and the Ø16 hole as a true circle. The top view should show the 80 mm × 50 mm base, the Ø10 hole position and the web thickness. Those two views can define the part if the web thickness and hole depth are dimensioned.
A right-side view is not automatically needed; it would show the 12 mm web as a visible rectangle and the hole through the web, but it adds little if a section is used. A better choice is a local or staggered section through the web hole, replacing the hidden lines in the top view. A full section through the vertical Ø10 hole is not the best section because it cuts the base but misses the inclined web and the Ø16 hole. If the two hole axes lie in one cutting plane, use a staggered section through both; if not, use two local sections or a removed section for the web.
2. The Ø16 circle is broken by hidden lines. Explain the line-precedence rule and whether those hidden lines should be removed.
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Visible outlines take precedence over hidden lines. The Ø16 circle is a visible feature in the front view, so hidden lines from the web or base should not be drawn across it. Where a hidden line coincides with a visible line, the visible line is shown; where hidden detail is fully defined by a section, the hidden lines in that view are normally omitted.
In this drawing, the hidden lines that break the circle should be removed. Hidden lines should be retained only where they are needed for manufacture and are not shown by a section or another view. Centre lines should remain, because they locate the hole. Removing the hidden lines will also make the sheet less crowded without losing information.
3. Explain why a centre line is required at the left-hand end of the inclined face and where it should extend.
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The Ø16 hole needs a centre line in every view where it appears, because the centre line is the datum for the 25 mm height and the 20 mm set-off. Without it, the hole position on the inclined face is ambiguous and the 30° face has no reference line for dimensioning.
The centre line should be a long-dash-dot thin line. In the front view it should pass through the centre of the Ø16 circle and extend 3–5 mm beyond the circle. In the top view it should locate the hole axis and align with the front view. It should not be used as a dimension line or as an outline. If the inclined face is later shown in an auxiliary view, the same centre line should be projected into that view.