1. Curved Surfaces and Centerlines
Sections and of Text

2. Objectives
Understand how curved surfaces will appear in each viewing plane.
Create orthographic projections of objects with curved surfaces.
Correctly use center marks and center lines to add clarity to drawings.

3. Curved Surfaces in orthographic
Similarly to the way inclined surfaces appear as an inclined edge in one view, curved surfaces will appear as a curved edge in one view and as a plane in the two remaining views.

4. Orthographic Projection of a Cylinder
The figure below shows an orthographic projection of a cylinder
Centerlines and centermarks are used to denote the center of a circular or cylindrical feature.
Centerlines
Visible extents of cylinder
Centermark
CLICK
Circular end of Cylinder

5. Centerlines
In order to help others understand your drawings, it is necessary to include centerlines and centermarks.
A centerline alerts readers that the edges next to the centerline may be optical limits of a curved surface and not true sharp edges.
This case occurs every time a curved surface is shown as a plane.
The most common occurrence of a curved surface in engineering drawings is a hole with hidden and center lines.

6. Centerlines
Centerlines are drawn by alternating long and short dashes along the length of the center of the cylinder or a circular hole.

7. Centermarks Centermarks show the center of a circular feature.
This arc is 180°
This arc is 90°
Visible limit of arc
Hidden lines
Center lines
Center line
Hidden
lines
Centermark
Centermark, note the extension lines
Centerline and centermarks are used where the arc of a surface is 180° or greater.
Note that both centerlines and centermarks extend past the extents of the circle or circular feature.

8. Line Precedence Visible lines takes precedence over all other lines
Hidden lines take precedence over center lines
Center lines have lowest precedence
In this drawing, a visible line overlies a centermark.
Notice that the extension lines from the centermark are still visible.

9. Curved Surfaces and Centerlines
Use this time to practice making orthographic projections from objects with curved surfaces.
Do not forget to include centerlines and centermarks as needed!
In class assignment