1 4. Principles of Dimensioning This week you will learn dimensioning. The steps to follow are: Functional & Non-functional Dimensions Principles of Dimensioning Dimension Placement & Conventions Dimension Tolerances Geometric Dimensioning & Tolerancing Assignment #4

2 4. Principles of Dimensioning What is dimension ? Dimensions are defined as numerical values expressed in appropriate units of measure and indicated on a drawing and in other documents.

3 4. Principles of Dimensioning FUNCTIONAL DIMENSIONS Functional dimensions directly affect the function or working of a product and may be of the size or location types. A datum is a reference line on the drawing from which a component is dimensioned. In practice, a datum is any functional surface or axis used for manufacture, inspection, location, or assembly purposes. NON-FUNCTIONAL DIMENSIONS Non-functional dimensions, NF in Figure, are those dimensions which are used for production purposes but which do not directly affect the function or working of a product. Non- functional dimensions usually are not inspected.

4 4. Principles of Dimensioning

5 PRINCIPLES OF DIMENSIONING Dimensions are normally expressed in millimeters. Dimensions of less than unity should be preceded by zero Each dimension should appear only once It should not be repeated on other views. Dimensions relative to a particular feature should be placed in one view, which shows the relevant features most clearly, rather than spread over several views.

6 4. Principles of Dimensioning AUTOMATIC DIMENSIONING Some more powerful CADD systems allow dimensions to be added automatically to a drawing. In a drawing made by hand, there is no necessary or inherent correspondence between the dimensions of the drawn outline and the intended dimensions of the object, which it represents, until a scale has been specified.

7 4. Principles of Dimensioning Dimensioning Concept CADD software such as AutoCAD provides three basic types of dimensioning: linear (horizontal, vertical, aligned, rotated, ordinate, baseline and continued), radial and angular.

8 4. Principles of Dimensioning Dimensioning System Variables The dimensioning system variables control the appearance of dimensions. You may set these variables on the command line Variable Value Explanation. Dimasz Controls the size of the dimension arrowhead Dimgap Sets the distance around the dimension text above its line Dimexe Determines how far to extend the extension line Dimexo Determines how far extension lines offset from origin point Dimdli Sets the distance between adjacent dimension lines Dimrnd Rounding dimension text value

9 4. Principles of Dimensioning Arrowheads

10 4. Principles of Dimensioning Special Characters Diameter %C Ø %C 50 Ø 50 Degree %D ° 50 %D 50 ° Plus/minus %P ± 50 %P 2 50 ± 2

11 4. Principles of Dimensioning Linear Dimensions

12 4. Principles of Dimensioning Chain Dimensions

13 4. Principles of Dimensioning Radial Dimensioning

14 4. Principles of Dimensioning Angular Dimensioning

15 4. Principles of Dimensioning Text Justification Centered Above Aligned & Centered Above Outside

16 4. Principles of Dimensioning Text Fitting Rounding off Dimensions

17 4. Principles of Dimensioning DIMENSION TOLERANCES Tolerance is the total amount that a specific dimension is permitted to vary; it is the difference between the maximum and minimum limits for the dimension. Tolerances can be applied directly to dimensioned features, using limit dimensioning.

18 4. Principles of Dimensioning Applying Dimension Tolerances in AutoCAD

19 4. Principles of Dimensioning Geometric Dimensioning & Tolerancing

20 4. Principles of Dimensioning Geometric Dimensioning & Tolerancing  

21 4. Principles of Dimensioning Basic Dimensions Basic dimensions are the theoretical sizes from which limits of size are derived by the application of allowances and tolerances.

22 4. Principles of Dimensioning Next Week ; You will learn creating sectional views. The steps to follow are: Cutting plane Types of sectional views (full, half, detailed etc) Hatching Assignment # 5

23 4. Principles of Dimensioning Assignment # 3 You will sketch the three views for an objects in 1st angle projection & give all necessary dimensions. Don’t forget to save it! Submit the assignment on time by logging into  

24 4. Principles of Dimensioning Assignment Procedure Open ISO_A3 template file Format the drawing file (linetype etc) Sketch the front view Use construction line Complete the top view and the side view Fill in the title block (name, number, date etc) Save your file into Z disk (i.e. YourNumber_YourNameSurname_A3.dwg) (i.e. YourNumber_YourNameSurname_A3.jpeg) 