GD&TGeometric Dimensioning & Tolerancing

ASME Y14.5 (1994)

TECH 4472 & TECH 4571

Dimensioning & Tolerancing

Know the general rules Y14.5 Section 1.4For example:● All dimensions must have a tolerance● D&T must completely define geometry● Define the finished part. Helpful dimensions

must be REF.● Avoid descriptions of manufacturing

methods. Define geometry, not method.● Should be readable● Should be applied to visible lines

● Wire, sheet, cable, rods manufactured to gage or code numbers shall be specified by linear dimensions indicating diameter or thickness. Gage or code number may be shown in parentheses.

● Angles of 90° are assumed if perp. with no angular dimension.

● Dimensions and tolerances are valid at 20° C unless otherwise noted.

● Dimensions apply to free state.● Dimensions & tols. apply to full length, widh

and depth of feature.● Apply only at the level of the drawing where

they appear.

Units of Measure

•Indicate on the print a note such as:UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN MILLIMETERS (or INCHES).•Millimeter Dimension–Zero precedes the decimal point.–If the dimension is a whole number, do not include a decimal point or trailing zero.–Do not include trailing decimal zeros.–Do not use commas or spaces to group digits.

Units of Measure

•Decimal Inch Dimensioning–Do not precede dimension with a zero.–A dimension is expressed to the same number of decimal places as its tolerance. –Use trailing zeros as necessary.

Units of Measure

General Tolerancing

•Limit Dimensioning•Plus and Minus Tolerancing–Unilateral–Bilateral–Bilateral Symmetric

Angle Tolerance

General Advantage of GD&T

Consider the following:

Think about the tolerance zone

Think about the tolerance zone

How much can the center be away from target?

hmmmm....

Table Example

Table Example

Using GD&T Flatness

Rule #1

•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. (ASME Y14.5M – 1994)

Rule #1

Rule #1

•Two sides to rule number 1:–Limits of size prescribe limits of form

•Allows variation in form–Limits of size prescribe limits of form

•Prohibits variation in form

Feature Control Frame

Feature Control Frame

Types of Geometric Tolerances

FORMSTRAIGHTNESSFLATNESSCIRCULARITYCYLINDRICITY

PROFILEPROFILE OF A SURFACEPROFILE OF A LINE

Types of Geometric Tolerances

ORIENTATIONPARALLELISMPERPENDICULARITYANGULARITY

RUNOUTCURCULAR RUNOUTTOTAL RUNOUT

Types of Geometric Tolerances

LOCATIONCONCENTRICITYPOSITIONSYMMETRY

Basic Dimension

Actual Mating Envelope

Material Condition Modifier

Know about the Bonus Tolerance

Datums

Surface Vs. Center Plane Datums

Axis Datums

Datum Targets

Example