Dimensioning

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ENGR 111 12.2a Basic Dimensioning with AutoCAD

How to annotate simple drawings for use in constructing an object

Learning Objectives

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Be able to understand the basic rules of dimensioning Apply dimensions to objects in accordance with engineering standards Define the following items: Dimension line, Extension line, Reference dimension, and Leader Be able to recognize the following machined holes: Spotfaced, Counterbored, Countersunk, & Counterdrilled.

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Basic Dimensioning

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Dimensions allow a part to be manufactured Dimensions are ALWAYS in real world units Dimensions should be applied in a concise, coherent manner

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Dimension Terminology:

DIMENSION LINE

3.00 1.80 .80 .90 1.00

EXTENSION LINE ARROWHEAD EXTENSION LINE: EXTENSION GAP

LEADER

2.00 1.00 1.20

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Extension lines

Extension lines should be offset from the part by one half the text height and should extend one text height beyond the dimension line

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Dimension Spacing

The first row of dimensions must be a minimum of 3 text heights away from the part. Any dimensions beyond it must be a minimum of 2 text heights apart

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Arrowheads:

Should be 3 times longer than they are wide.

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Dimensioning Rules

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Avoid placing any dimensions on the part (inside the view) unless there is no other option. Avoid dimensioning to hidden features Always place the dimension where the characteristic shape is shown in the most descriptive view. (This means don’t place a dimension on object lines making a “T joint”.) Always dimension holes in their circular view by stating the diameter of drilled holes. Specify the hole depth of special features such as countersinking with a note following the dimension. Dimension rounded corners and arc features as radii...