Dimensioning Symbols and Principles Quiz

Applying Dimensioning: A Guide to Symbols and Principles

When designing technical drawings, dimensioning is a crucial practice that helps communicate essential information about an object's size, shape, and position. This article will explore the world of dimensioning, focusing on the fundamental symbols and principles involved.

Dimensioning Symbols

1. Extension Lines: These lines extend from the reference line or reference surface to the dimension line. Extension lines help visualize the actual length, depth, or width being measured.

2. Dimension Lines: These lines connect the extension lines and indicate the dimensions being described. They may be vertical, horizontal, or angled, depending on the geometry of the object.

3. Leader Lines: These lines, often arrow-tipped, connect the dimension text to the object being measured. They help clarify the relationship between the text and the referenced feature.

4. Dimension Text: This text, written next to the leader line, denotes the actual dimension being measured or described.

5. Supplementary Dimensions: These dimensions clarify or call attention to specific aspects of a drawing that might be unclear based solely on primary dimensions. For example, a supplementary dimension might call out a radius, thickness, or angle.

6. Abbreviations and Symbols: These additions simplify dimensioning by providing standardized representations for common measurements and units. For example, the symbol "Φ" indicates a circular diameter and "D" indicates a linear dimension.

7. Arrowheads: These markers indicate the direction in which a dimension should be read. They typically point to the larger dimension and are used in conjunction with supplementary dimensions.

8. Tolerances: These symbols indicate a range of acceptable variation in size, shape, or position. There are two types of tolerances: bilateral (±) and unilateral (∓), which allow for variation in either direction or only one direction, respectively.

Principles of Dimensioning

1. Precision: Dimensions should be accurate and detailed enough to fully describe the object being represented.

2. Clarity: Dimensions should be easy to read and understand, and they should accurately reflect the dimensions of the object being represented.

3. Consistency: The same terminology and symbols should be used throughout a drawing, and dimensions should be consistent in their placement and orientation.

4. Restrictions: Dimensions should be placed where they will not interfere with other dimensions, and they should not obscure information on the drawing.

5. Alternative dimensions: Dimensions should be placed in a way that allows for alternative dimensions to be easily added if necessary.

6. Annotations: Dimensions should be accompanied by appropriate annotations that explain the context or method of measurement.

7. Tolerances: Dimensions should be accompanied by appropriate tolerances that indicate the acceptable range of variation in the component's size, shape, or position.

8. Standard practices: Dimensioning should adhere to standard practices and conventions, such as the ASME Y14.5 standard, which specifies dimensioning and tolerancing practices for engineering drawings.

By understanding dimensioning symbols and principles, you can confidently apply dimensioning techniques to create clear and accurate technical drawings. Remember, simple and straightforward dimensions are often the most effective.