Question 1 of 6: Orthographic Views, Dimensioning & Feature-Based CAD Sequence

Question 1: Orthographic Views, Dimensioning & Feature-Based CAD Sequence (40 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 pictorial. The part is a rectangular block, about twice as long as it is deep or high. Three features are cut from it:

• A ramp between the two end blocks. Between a narrow left end block and a narrow right end block, the front of the block is cut away by an inclined plane. The plane runs from a horizontal line on the back wall, about two-thirds of the way up, down to the bottom front edge. Above that line the remaining back wall rises vertically to the full height. The left end block's inner face (lit, facing the right) shows the ramp as a sloping edge.
• A vertical through-hole centred on the back-wall face. The hole's axis lies in the plane of the back wall, at mid-length. The back half of the hole is cut into the full-height wall and shows as a semicircle in the top face. The front half pierces the ramp, which gives the long elliptical opening. The small arc at the bottom of the opening is the far edge of the hole where it leaves the underside, so the hole goes right through.
• A 45° chamfer along the top-front edge of the left end block only. The right end block is a plain full-height rectangle.

a) The Front View is taken looking at the long face, because that face shows the chamfer, the two end blocks, the ramp opening and the hole most clearly. In third-angle projection the Top View goes directly above the Front View, with its lower edge representing the front of the part, and the Right-Side View goes directly to the right of the Front View, with its left edge representing the front. Width projects from the Front View up to the Top View, height projects across to the Right-Side View, and depth transfers between the Top and Right-Side Views.

What each view shows:

• Front: the full-height outline; the chamfer as a horizontal line across the left end block; vertical lines where the end blocks meet the cut; the ramp-to-wall edge as a horizontal line about two-thirds up. The hole shows as two vertical visible lines in the wall above that edge, joined by the U-shaped curve where the hole passes through the sloping ramp. Below the U, the hole's sides are buried in the ramp material, so they are hidden, dashed down to the base.
• Top: the rectangular outline, the chamfer edge on the left end block, the two short end-block edges, and the back-wall line. That line is interrupted by the hole, which appears as a full visible circle centred on it: the back half is in the top face and the front half is on the ramp, and a vertical cylinder projects to the same circle either way.
• Right side: the silhouette is a plain square, because the right end block is full size. Everything else sits behind it and is dashed: the chamfer diagonal, the ramp's slope line, the back-wall face above the ramp, and the hole's two side lines. The rear side line runs full height; the front one is short, because the ramp leaves little material there.

b) Dimensioning follows ASME Y14.5 practice. Extension lines start a small gap off the object, dimension lines sit outside the views, and smaller dimensions go nearer the view with the overall dimensions outside them. Each size is given once, in the view where its feature is seen true and visible, and never to a hidden line. Values are replaced by “xx” as instructed.

• Front View: overall length and height; the widths of the left and right end blocks (these fix the length of the ramp cut); and the height of the ramp-to-wall edge, taken to the visible line.
• Top View: overall depth; the depth of the back wall, measured from the back face, which locates the top of the ramp; the hole diameter as a leader note “⌀xx THRU”; and the hole's location from the left end. Its centre lies on the back-wall line, which is already dimensioned.
• Chamfer: a leader note “xx × 45° CHAMFER”. A separate height for the front face of the left end block would repeat this and over-dimension the part, so it is left off.
• The Right-Side View carries no dimensions, because every feature in it is hidden.

c) A parametric, feature-based modeller stores the part as an ordered history. The base feature comes first, the cuts follow, and dress-up features such as chamfers come last, so that each feature references geometry that already exists and edits regenerate cleanly:

1. Base extrude. Sketch a rectangle (length × depth) on the Top plane and extrude it upward by the overall height.
2. Ramp: extruded cut. On the Right plane, sketch the side profile of the removed wedge: the vertical back-wall line, the sloping ramp line down to the bottom front corner, and the top and front edges. Constrain the ramp line to the bottom front edge and dimension the wall depth and the ramp-top height. Extrude-cut the profile mid-plane by the distance between the end blocks. A mid-plane cut keeps the ramp symmetric about the part's centre plane when the length changes.
3. Hole: extruded cut, Through All. Sketch a circle on the top face. Make its centre coincident with the back-wall edge and place it on the mid-length centre line, then cut Through All. These relations, not typed coordinates, keep the hole on the wall if the wall depth or part length is later edited.
4. Chamfer. Apply a 45° equal-distance Chamfer feature to the top-front edge of the left end block. It goes last because it is a dress-up feature on an edge that only exists after step 2.

An equally valid variant is to sketch the whole stepped-and-sloped side profile once and extrude it the full length, then add the two end blocks as extruded bosses. The subtractive order above is closer to how the part would be machined.