CHAPTER 9 GEOMETRIC DIMENSIONING & TOLERANCING ( GD&T ) Reference = http://www.emachineshop.com/machine-shop/GD-T-Symmetry-Definition/page619.html http://www.gdandtbasics.com/

1. Tolerance - amount by which the dimension is allowed to vary - applied to position & size

2. GD&T Method of dimensioning & tolerancing a drawing with respect to the actual function or

relationship of the part feature that can be most economically produced International language to describe the part accurately Include symbols, rules & definition for defining a geometry of the part Uniformity in drawings, better design, enhance repeatability

3. Definition

Dimension ( numerical value to define SIZE, LOCATION, ORIENTATION, FORM or other CHARACTERISTICS)

Feature ( physical portion a part, eg. hole, surface, slot) Feature of Size ,FOS (cylindrical/ spherical surface) Datum (coordinate system to locate the places, eg. plane, point, axis) Datum reference frame (2 mutually perpendicular datum plane, eg. X, Y, Z-axos)

4. Language of GD&T

a) Form tolerance - 5 b) Profile tolerance - 2 c) Orientation tolerance - 3 d) Location tolerance - 3 e) Runout tolerance - 2

FPOLR-52332

A. Form Tolerance - State how far the actual surface or feature is allowed to vary from the desire form of the drawing

Symbol

Name Definition Diagram

Straightness (of an axis)

Condition where all the points on the surface of an axis are in straight line The axis must lie within cylindrical tolerance zone of 0.03mm

Straightness (of a surface)

Flatness Condition of a surface having all the points in 1 plane The surface must lie between 2 parallel plane 0.18mm apart and the surface must within the specified size limit

Circularity Condition where all the points on a surface are in a circle Circular element must lie between 2 concentric circles where the difference of the radi of 2 circles is 0.05mm.

Cylindricity Condition where all points of a surface are

equidistant from the common axis The cylindricity tolerance specifies a zone bounded by 2 concentric cylinder within which the measured surface must lie.

B. Profile Tolerance -states how far an actual surface or texture is allowed to vary from the desire form on the drawing or vary relative to a datum Symbol Name Definition Diagram

Profile of a line

The outline of an object in a given plane. The tolerance zone is established by 2 dimensional extending along the length of the considered feature The line element must lie between 2 profile boundaries 0.6m apart in relation to datum A.

Profile of a surface

The tolerance zone is established by the profile of a surface tolerance is 3 dimensional extending along the length and width All points on the surface must lie between 2 profile boundaries 0.6mm apart in relation to datum plane A

C. Orientation Tolerance - States how far an actual surface or feature is permitted to vary relative to a datum

Symbol Name Definition Diagram Angularity Condition of a surface or axis at a specified angle

(other than 90 degree) from a datum plane or axis) Tolerance zone is defined by 2 parallel planes at specific basic angle form datum plane/ axis. All points must lie within 0.5mm wide tolerance zone.

Perpendicularity Condition of a surface or axis at a right angle to a

datum plane/ axis A zone defined by 2 parallel planes that are perpendicular to a datum plane or axis. The surface of the feature must lie within the zone which is 0.15mm wide & right angle to datum A.

The axis of hole must lie within the zone which is 0.3mm wide and at right angles to datum axis A.

Parallelism Condition of a surface or axis that are paralled to a datum plane/ axis A zone defined by 2 parallel planes to a datum plane or axis. The surface of the feature must lie within 2 planes 0.25mm apart which are parallel to datum A

D. Location Tolerance - State how far an actual size feature is permitted to vary from the perfect location implied by the drawing as related to a datum Symbol Name Definition Diagram Position Define a zone within which the center, axis or

center plane of a feature of size is permitted to vary from the true position The center of the holes must lie within circles of 0.5mm diameter when the holes are at10.25mm diameter Reference http://www.gdandtbasics.com/true-position/ Extra total permissible variation that a feature

can have can be used with MMC,LMC MMC_ can know the size, location &

orientation of the feature all at once. Hole [Gauge (pin gauge)=Min of

hole (MMC)-True Position Tolerance] Pin [ Gauge (hole gauge) = Max of

pin (MMC) + True Position Tolerance]

Concentricity Condition where the axes of all cross sectional elements of a surface of revolution are common to the axis of a datum surface. Concentricity tolerance specifies a cylindrical tolerance zone whose axis coincides with the datum axis The zone has a diameter of 0.2mm and the feature axis must lie within this zone

Symmetry Symmetry tolerance establishes a tolerance zone

for the median points of non-cylindrical part features. The median points of these opposing surfaces must be symmetric about datum axis A within a tolerance zone of 0.7 The median points must lie between two planes 0.7 apart and equally spaced about datum axis A.

E. Run out Tolerance how far an actual surface or feature is permitted to vary from the desired form implied by the drawing during full 360 degree rotation of the part on the datum axis. Symbol Name Definition Diagram Circular Runout Runout is how much one given reference feature or

features vary with respect to another datum when the part is rotated 360 around the datum axis. It is essentially a control of a circular feature, and how much variation it has with the rotational axis. Runout is measured using a simple height gauge on the reference surface. The datum axis is controlled by fixing all datum points and rotating the central datum axis. Each circular element for the surfaces tolerance must fall within 0.04mm( when the part turn 360 degree about datum axis) When the shaft rotating, with datum A fixed in housing, the reference surface will not go outside of a perfect central rotation by more than 30 microns.

Total Runout Total Runout is how much one entire feature or surface varies with respect to a datum when the part is rotated 360 around the datum axis. Both radial variation and axial variation are measured Total Runout is measured by fixing the all datum points and rotating the part along the rotational axis. Control = circularity, straightness, coaxiality, angularity, taper, profile of a surface This entire surface must have full indicator movement (FIM) of less than 0.1 relative to datum A" Full Indicator Movement (FIM) is the absolute difference between the minimum and maximum reading of an indicator as a workpiece is rotated a full revolution. FIM is used to establish whether a part meets its runout or total runout tolerance. When measuring a part, the indicator measurement device (shown in the left figure below) is placed on the part. As the part is rotated, the indicator fluctuates between its min and max positions based on the highest and lowest points on the part. The absolute difference between the final min and max positions establishes the FIM of the part.

5. Modifier - Material condition Maximum material condition (MMC)

Definition Condition in which a feature-of-size that contains the greatest amount of material, yet remains within its tolerance zone. Symbol

Application Largest pin diameter Smallest hole diameter

Example

Least material condition (LMC)

Definition Condition in which a feature-of-size that contains the least amount of material, yet remains within its tolerance zone. Symbol

Application Smallest pin diameter Largest hole diameter

Example

6. Feature control frame Compartment Function First Geometric symbol Second Tolerance info & value Third, forth.. Related datum