Ch.9 Dimensioning

Why do we need dimensions? Important elements of a dimensioned drawing Dimension text placement Unidirectional vs. aligned dimensions Where and how should we place dimensions Dimensioning guidelines (we cover 2, 3, 4, 5,

7, 9, 10 and 13, pages 505-506 today)

Objective: Learn the rules of dimensioning. Terms you learn in this chapter have direct relevance to dimensioning by CAD.

An engineering drawing will have graphics, dimensions, and words or notes to fully define the part.

Why do we need dimensions? Once the shape of a part is defined with an orthographic drawing, the size information is needed to make the part physically.

Important elements of dimensioning

Two types of dimensioning: (1) Size and location dimensions and (2) Detail dimensioning

Elements of a dimensioned drawing (Be familiar with these terms

Dimensioning standards

Dimension text placement

Unidirectional or aligned dimensioning?

Dual dimensioning

Dimension guidelines (pages 505-506)

2. Double dimensioning of a feature is not permitted.

This guideline is related to tolerance. We will discuss it when we discuss tolerance.

Dimension guidelines (pages 505-506)

3. Dimensions should be placed in the view that most clearly describes the feature being dimensioned (contour (shape) dimensioning)

Dimension guidelines (pages 505-506)

4. Maintain a minimum spacing between the object and the dimension between multiple dimensions.

5. A visible gap shall be placed between the ends of extension lines and the feature to which they refer.

Dimension guidelines (pages 505-506)

7. Avoid placing dimensions within the boundaries of a view, whenever practicable.

9. Unless otherwise specified, angles shown in drawings are assumed to be 90 degrees.

Dimension guidelines (pages 505-506)

10. Avoid dimensioning hidden lines.

13. Leader lines for diameters and radii should be radial lines.

Where and how should we place dimensions when we have many dimensions?

Guide 2

Guide 7

Where and how should we place dimensions when we have many dimensions? (cont.)

Guide 13

Guide 7

Guide 2

Where and how should we place dimensions when we have many dimensions? (cont.)

Where and how should we place dimensions when we have many dimensions? (cont.)

Guide 2