# Dimensioning and Tolerancing

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Dimensioning and Tolerancing
David Quigley February 7, 2006

Dimensioning Definition:
A dimension is a numerical value expressed in appropriate units of measure and indicated on a drawing A dimensioned drawing should provide all the information necessary for a finished product or part to be manufactured.

Dimensioning Example An example dimension is shown below.

Rules for Dimensioning
Use one type of dimensioning consistently General units can be omitted if stated somewhere on the drawing Projection lines do not touch the object and are drawn perpendicular to the element you are dimensioning. All dimensions less than 1 should have a leading zero. i.e. .35 should be written as 0.35

Types of Lines Thin chain lines indicate center lines.
Dashed lines are for hidden lines. Center Lines Hidden Lines

Types of Dimensioning Parallel Dimensioning
Has several dimensions starting from one projection line.

Types of Dimensioning Chain Dimensioning
Having the dimensioning start after each previous dimension Chains of dimension should only be used if the function of the object won't be affected by the accumulation of the tolerances.

Types of Dimensioning Combined Dimensioning
This type combines Chain and Parallel Dimensioning

Types of Dimensioning Dimensioning Holes
Holes can be dimensioned with coordinates

Dimensioning Holes

Stagger Dimension Values

How to dimension small objects
When dimensioning small features, placing the dimension arrow between projection lines may create a drawing which is difficult to read. So, use one of the below techniques.

Dimensioning Circles All dimensions of circles are proceeded by this symbol; . There are three different ways to dimension circles

Circle Dimensioning (a) two common methods
(b) Used when the circle is too small (c) outside dimensioning

Tolerancing Definition:
The total allowable variation an acceptable part can have from the specified dimension. The less variation allowed, the more the part will cost to make

Complicated Example

Tolerancing Rules Each dimension on a drawing must include a tolerance value. a general tolerance value applicable to several dimensions. i.e. a note specifying that the General Tolerance +/- 0.5 mm. or a tolerance specific to that dimension

Tolerancing Example The upper limit for the tolerance goes on top of the lower limit.

Dimensioning Exercises
Complete the Handout Exercise