ENG 004 Lecture 15, Nov 15, 2012

Announcements

• Homework #6 due Tuesday, any questions?

Topics

• Geometric Dimensioning and Tolerancing

Tolerancing

Tolerancing is the art and science of using the largest tolerance possible that will still allow a part to function.

Geometric Dimensioning and Tolerancing

• A method of defining parts based on how the function, using standard ASME/ANSI symbols.
• Size cotnrol is the first rule
• Supplements size control in that it allows for feature/geometry control
• It uses a symbolic language

Rule #1

Individual Feature of Size

Where only a tolerance of size is specified, the limits of size of an individual feature prescribe the extent to which variations in its geometric form, as well as size, are allowed.

i.e.

If a feature is dimensioned only with a traditional tolerance, then that tolerance governs all of the tolerances for form. You only specify geomtric dimensions and tolerances to supplement the tradiational size/location tolerance.

Datum

A starting place for a dimension such as a perfect plane, a center line, or a point.

Datums are perfect, ideal constructs

In reality "perfection" of a datum can mean that it is at least 10 times more accurate than the accuracy of the part being measured.

Feature Control Frame

Used to specify the geometric tolerances. It is divided into two or more zones.

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