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### Curved Surfaces and Centerlines

Sections 11.02 and 10.07 of Text

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.

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.

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

Circular end of Cylinder

CLICK

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.

Centerlines

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

Centermarks

Hidden

lines

- Centermarks show the center of a circular feature.

This arc is 180°

- 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.

Center line

Centermark

This arc is 90°

Centermark, note the extension lines

Visible limit of arc

Hidden lines

Center line

Hidden

lines

Center lines

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.

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

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