Engineering Drawing Question

Q: I got the following question on my first year engineering design course's midterm, and I was wondering if anyone agrees with the answer (I think the question are very ambiguous and really has no proper answer). Which of the following types of drawings show all dimensions on the principal axes as true dimensions? a) Isometric projection b) Persepctive drawing c) Three view drawing (orthographic) d) None of the above do e) They all do I think there are no correct answers (becasue both Iso and 3-view drawings have true dimensions on x,y,z axes). What does everyone else think?

A: -Isometric views do not necessarily show true dimensions, therefore the correct answer is C. To me it's unambiguous . . . but then I come from the "old school" that did drafting on the board before the advent of CAD. -Isometric drawings *do* show true sizes in all three dimensions . 3-D CAD renderings are the ones that can't be scaled on paper. I, too, started on the board many years ago and have drawn thousands and thousands of isometric pictorials (I still favor them over 3-D). How could you draw them to scale if they weren't true in all three dimensions? Perhaps you are confusing them with "two-point perspective" or maybe "oblique" drawings (which, ironically, are also scalable in the three axes). A true isometric drawing is based on 30 deg. and vertical drawing angles and all dimensions in the three principal axes are true and scalable. You might start some semantic argument that an isometric can be drawn based on other angles or variable scales, but you would be wrong. This is why they make templates of 35.26 deg. "isometric" ellipses: so that you can draw circles on an isometric drawing in all three axes (the circles are scalable in these axes as well; that's why their diameters are given on the template). Extra Credit: can you show why the isometric elliptic angle is approx. 35.2644 degrees?

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