Learning Targets
- Recognize the long-short-long centerline pattern.
- Place centerlines through circular and cylindrical features.
- Use centerlines to communicate symmetry and axes.
- Distinguish centerlines from object and hidden lines.
IED Unit 1 • Lesson 1.2 • 1 class period
Centerlines & Symmetry
Focus question: How do engineers show the center of a circular or symmetric feature without drawing a physical edge?
Mission Briefing
What You Are Learning
Use this webpage, your engineering notebook, and the listed lesson resources to complete the work in order.
Success Looks Like
Use centerlines to communicate axes, centers, and symmetry without confusing them with visible or hidden edges.
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Class Flow
Work Through the Lesson
- Identify the centerline pattern in sample drawings.
- Add centerlines to holes, circles, cylinders, and symmetric shapes.
- Compare correct and incorrect centerline placement.
- Complete a short practice set and self-check your line types.
Core Ideas
What to Pay Attention To
A centerline shows the axis of a hole, cylinder, or other rotational feature.
Two perpendicular centerlines can locate the exact center of a circular feature.
A centerline can show that geometry is intended to be symmetric about an axis.
Engineering Check
Stop and verify before moving on
A centerline represents an axis or center—it is not a physical edge. Do not replace visible or hidden edges with centerlines.
Your Task
Complete the Centerlines & Symmetry Worksheet
Work through the worksheet problems by identifying circular, cylindrical, and symmetric features. Add centerlines only where they communicate a useful center, axis, or line of symmetry.
- Identify every circular, cylindrical, or clearly symmetric feature.
- Decide whether a centerline is needed in each view.
- Draw centerlines using a consistent long-short-long pattern.
- Extend centerlines slightly beyond the feature when appropriate.
- Review the drawing to make sure line types are visually distinct.
Use evidence: Keep sketches, measurements, observations, and revisions visible. Unit 1 is building one connected engineering documentation package.
What You Will Submit
Centerlines & Symmetry Practice
Before submitting: Check that your work is labeled, readable, complete, and consistent with the technical conventions used in this lesson.
Resources
Lesson Resources
Open the files you need for today’s work.
Centerlines & Symmetry Worksheet
Practice locating centers, axes, and lines of symmetry and applying centerlines correctly to technical views.
Multiview Sketch Paper
Use the orthographic quadrants for additional centerline practice.
IED Unit 1
Return to the unit overview for the full documentation and product-improvement sequence.