1. Introduction to Engineering Multi-view Drawings - 2
Agenda
Hidden Lines & Center Lines
Precedence of Lines
Conventions for Line Intersections
Reference - IGCE, Chap 2: Sections 5 and 6
Sketching - 5

2. Defining Hidden and Center Lines
Hidden Line – used to represent features that cannot be seen in the current view
Centerlines – used to represent symmetry and to mark the center of circles and the axes of cylinders, and the axes of symmetrical parts, such as cylinders and bolts
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3. Example Center Line Visible Line Hidden Line
From Bertoline: Figure 30 / Pg 38
In engineering and technical drawing, it is important that hidden features be represented, so that the reader of the drawing can clearly understand the object.
Thus we need hidden lines to emphasize that those features exist and are hidden in that particular view.
We also need center lines to understand how the features defined in the 2D views translate into 3D.
Q: Do we need a convention for what line to show if two lines fall on top of each other?
A: Yes! Otherwise features which are more important (eg: visible lines) would be overridden by less important features (eg: hidden lines) and the resulting drawing would be interpreted inaccurately. The next slide shows the convention followed.
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4. Precedence of Lines 0.6 mm 0.3 mm 0.3 mm
From: Bertoline, Figure 32/ Pg 39
The precedence of lines governs which lines are drawn when more than one line occupies the same position on a drawing.
For example the figure above shows that while a visible line takes precedence over all other lines, hidden line and cutting plane line take precedence over center lines.
Standard engineering drawing practice requires the use of standard linetypes, which are called the alphabet of lines. The sizes show the recommended line thicknesses.
0.3 mm
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5. Example: Application of Precedence (See Figure 2.41 in IGCE)
Slide rearranged.
This slide shows the precedence of
Visible over hidden lines
Hidden over center lines (Note observation D)
Visible over center lines
(D) Note that the center lines still show but are drawn away from the hidden line and visible line in the right side view.
(E) Note gap between body and start of center lines.
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6. Conventions for Intersection of Lines (See Figure 2.40 in IGCE)
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7. Assignment #6 Assignment #6: Bertoline, Problem 2.9
Pg. 56, # (11)
Pg. 57, # (16)
Pg. 59, # (39)
Draw both the isometric and the top, right, and front vies on the handouts in the assignment packet. Remember to put the views in the proper locations.
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