Section view of a post-and-base part (offset section): 04-BS-15, May 2018, Q4

Question 4: Section view of a post-and-base part (offset section) (10 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.

[Figure not reproduced: source figure. See the official exam paper or the cited reference text.]

Source figure (exam p. 5), reproduced for reference.

Reading the views. The part is a rectangular base plate with a counterbored hole at each corner (the circle-in-circle symbols in the top view, and the stepped hidden lines in both lower views). A solid cylindrical post stands at the centre of the plate and carries a concentric bore. In both lower views the bore's hidden lines run from the top of the post and stop at the plate's top surface, so the bore is blind, as deep as the post is tall. Nothing is printed below the post inside the plate. The only internal features are therefore the bore and the four counterbored holes.

Approach

A section is chosen so that every internal feature is shown cut, with no hidden lines. A full section on the centre plane would show the bore, but it misses all four holes, which lie off that plane. The better choice is an offset section A–A. Its cutting plane enters through the front pair of counterbored holes, steps back to pass through the post axis, and steps forward again through the other front hole. It is viewed from the front and drawn in place of the front view. One view then shows the bore's diameter and blind depth, the post wall, and the hole-and-counterbore profile.

Fig. Q4 — top view with the offset cutting plane A–A (arrows give the viewing direction), and SECTION A–A drawn in the front-view position.

Conventions applied. The steps in the cutting plane are not drawn in the section; an offset section is drawn as if the part had been cut on one flat plane. The part is a single piece, so every cut surface is hatched with the same 45° general-purpose section lines at one spacing. Voids (the bore, the holes and the counterbores) are left unhatched. The section shows that the bore ends flush with the plate top, leaving solid plate beneath it. Visible edges behind the cutting plane are drawn, including the far rims of the bore and holes where they cross the voids, and hidden lines are omitted. The cutting-plane line is a heavy chain line labelled A–A, and the view is titled SECTION A–A. A full section on the centre plane, with the holes left to the top view and a callout, would also be acceptable, but the offset section is the more complete answer.

Topic: Offset and full section views; section-lining convention

Key relations: A cutting-plane line (heavy chain, labelled A–A, with arrows showing the direction of sight) marks where the part is cut. An offset section bends that plane through features that do not lie in one plane, and draws the result as if the plane were flat, with the steps not shown.

Why this works: The internal features of this part are the blind bore and the four counterbored holes, which do not share a plane. An offset plane through the post axis and a pair of holes exposes all of them in one view, and replaces every hidden line in the front view with a true, dimensionable profile.

Common pitfall: Hatching across the open bore or holes; drawing the offset steps as lines in the section; or inventing internal features. This bore stops at the plate top, as its hidden lines show, so no counterbore or through hole should appear under the post.

Source: Bertoline & Wiebe, Technical Graphics Communication, ch. on section views; Giesecke et al., Technical Drawing/Engineering Graphics, ch. on sectioning conventions.

Question 4 of 5: Section view of a post-and-base part (offset section)

Question 4: Section view of a post-and-base part (offset section) (10 marks)

Approach