By which of the following lines is the axis of the cylinder or sphere denoted?
Centre line
Representing Axes of Symmetry in Technical Drawing
In technical drawing, different types of lines are used to convey specific information about an object's geometry. The question asks about the line used to denote the axis of a cylinder or sphere. This axis is a line of symmetry for these objects.
Understanding the Centre Line
The Centre line is a fundamental line type used in technical drawings. Its primary purpose is to indicate axes of symmetry, the center of circles, and the path of motion or rotation. It is drawn as a long-short-long dash pattern, typically thin.
- A cylinder is symmetrical about its central longitudinal axis.
- A sphere is symmetrical about any diameter, but its center and implied axis are shown using Centre lines intersecting at the center.
Therefore, the Centre line is the standard convention for representing the axis of cylinders, cones, and spheres in technical drawings.
Other Line Types and Their Uses
Let's look at the other options provided and understand why they are not used for denoting the axis:
- Leader Line: A leader line is a thin line used to connect a note or dimension to a feature on the drawing. It typically has an arrowhead pointing to the feature. It is not used to show an axis.
- Section Line: Section lines (or cross-hatch lines) are thin lines drawn on cut surfaces of an object in a section view. They indicate the material that has been cut through. They are not used to show an axis.
- Hidden Line: A hidden line is a medium thickness dashed line used to represent edges or contours that are not visible in the current view. While an axis might sometimes be hidden, the line type specifically used to denote the axis itself is the Centre line, which takes precedence in indicating symmetry.
Conclusion
Based on the standard conventions of technical drawing, the line specifically used to denote the axis of a cylinder or sphere, which represents the line of symmetry, is the Centre line.
Revision Table: Common Technical Drawing Lines
| Line Type | Appearance | Common Uses |
|---|---|---|
| Visible Line | Thick, continuous | Visible edges and contours |
| Hidden Line | Medium, dashed | Hidden edges and contours |
| Centre Line | Thin, long-short-long dash | Axes of symmetry, centers of circles/arcs |
| Section Line | Thin, continuous (in patterns) | Cut surfaces in section views |
| Leader Line | Thin, continuous (with arrowhead) | Connecting notes/dimensions to features |
Additional Information on Axis Representation
The use of Centre lines for axes and centers is a fundamental rule in engineering and technical drawing standards (like ISO or ANSI). This convention ensures clarity and consistent interpretation of drawings across different fields and individuals.
- Centre lines extend slightly beyond the feature they represent.
- They should intersect at the center of circles and arcs.
- For symmetrical parts, a single Centre line can indicate the axis of symmetry for the entire view.
Correctly using Centre lines is crucial for accurately depicting symmetrical objects and their orientation.
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