Dimensioning

Why do we dimension drawings? Dimensioning Why do we dimension drawings? In order to provide accurate size description of a part for manufacturing. To describe the relationships between features in your drawing.

There Are 2 Basic Types of Dimensions Dimensioning There Are 2 Basic Types of Dimensions Size Dimensions Location Dimensions

5 Basic Rules to Remember Dimensioning 5 Basic Rules to Remember Start Small, Go Big Do Not Dimension to Hidden Lines or Hidden Features Avoid Placing Dimensions on Part Place Dimensions Between Views Do Not Dimension to Edge of Arcs

Dimensioning Key Terms Dimension Line Extension Line Finish mark Leader Dimension Offset Centerline Finish mark Dimension Value Baseline Dimensioning Chained Dimensioning

Dimensioning Key Terms

Dimensioning Key Terms Tolerance The total allowable variation a part can have from the specified dimension. The less variation allowed, the more the part will cost to make.

Dimensioning Leaders

Orientation for Dimension Values Dimensioning Orientation for Dimension Values Unidirectional: read horizontally from bottom of sheet Aligned: align with dimension line and read from bottom or right side of sheet

Unidirectional Orientation Dimensioning Unidirectional Orientation

Dimensioning Aligned Orientation

Stagger Dimension Values Dimensioning Stagger Dimension Values

Dimension & Extension Lines Dimensioning Dimension & Extension Lines

Dimensioning Finish Marks

Dimensioning Choice of Dimensions The dimensions you specify determine the way the the part is manufactured and the way the tolerance is applied Fully dimension each part Do not over dimension, Each dimensions should appear only once

Choosing Which Dimensions to Show Dimensioning Choosing Which Dimensions to Show Don’t over dimension! Give the diameter of circular shapes. Give the radius of arcs. No redundant dimensions Give size dimensions for features. Give location dimensions to show how features relate to one another.

Effect of Tolerance on Dimensioning Chained Each dimension continues from the previous one Tolerances stack Baseline Each dimension is specified from a common baseline Tolerances do not stack

Dimensioning Units Metric Metric values are typically given in whole millimeters or to one decimal place. 3 3.5

Placement of Dimensions Dimensioning Placement of Dimensions The rules for dimension placement help ensure that others will be able to interpret your drawing Where placement practices conflict, remember that your goal is to clearly communicate the purpose of the drawing. Use the practice you feel will make the drawing easy to understand.

Dimensioning Placement Practices Avoid dimensioning on object (face of part). Avoid dimensioning to hidden lines. Place dimensions between views when possible. Group dimensions around a central view. Place dimensions where feature shows shape. Dimension from or between machined surfaces Give overall dimensions where possible.

Dimensioning Dimensioning Holes

Dimensioning Using Diameter Symbol

Dimensioning Locating Holes

Dimensioning Summary Dimensioning drawings correctly can be as important or more important than drawing the shapes correctly. Good dimensioning requires practice and thought!