GD&T - PPT
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Transcript of GD&T - PPT
GD&T(Geometric Dimensioning & Tolerancing)
-Sreelakshmy (B.E)
Context
• Introduction• Revised changes made in ASME Y14.5 2009• Definitions• Symbols• Modifiers• Additional symbols• Datum• Datum symbols• Feature control Frame• GD&T in a part design (An example model)
Introduction
• GD&T is an international language used to describe a part accurately.
• It comprises of symbols, rules and definitions for defining a geometry of mechanical part.
• It has many benefits like uniformity in drawings, Better designs, No assumptions, large tolerances
• It is used especially in the manufacturing sector for dimensioning and Tolerancing
• The standard used was ASME Y14.5M-1994 and now, ASME Y14.5-2009 is used
Revised changes made in ASME Y14.5 2009
Important changes that has been made in 2009 version from 1999 are:
• Concept of FOS
• Datum References
• Degree of Freedom
• Composite Position Tolerances
• Surface Boundaries
• Axis Method of Interpretation
• Profile Tolerances
• Modifiers Tool
• Symbology
Definitions• Dimension
It is the numerical value expressed in units of measure to define SIZE, LOCATION, ORIENTATION, FORM or any other CHARACTERISTICS of a part
• Feature
• It is a general term applied to a physical portion of part such as surface, hole or slot
• FOS (Feature of Size)
It is a cylindrical/Spherical surface or set of two opposed elements associated with size dimensions
• Datum
It is a co-ordinate system used to locate places
• Datum Shift
It is the allowable movement between the part feature and the gage
• Nominal Value
It is the specified value on a drawing
• Tolerance
It is the total amount that part features are permitted to vary from their specified dimension
• Types of tolerances
Limit Tolerance, Plus-Minus Tolerance, Equal Bilateral Tolerance, Unequal bilateral tolerance, Unilateral Tolerance
Definitions Contd..
• Actual Local SizeIt is the value of any individual distance at a cross section of a FOS. It is a point-to-point measurement
• Actual Mating EnvelopeMeasure of distance between the highest points in a part design
• MMC (Maximum Material Condition)It is the maximum amount of material within the limits
• LMC (Least Material Condition)It is the least amount of material within the limits
• Bonus ToleranceIt is the additional tolerance permitted only when MMC or LMC is specified in the feature control Frame
• Regardless of FOSIt is the Geometric tolerance applied to any size the part is produced
Symbols & its characteristicsThere are 14 geometric characteristic symbols. They are categorized with
the type of geometric control (Form, Profile, Orientation, Location Run-Out)
Modifiers and its symbolsThey are symbols which defines conditions for the tolerance zone of a geometric tolerance. There are six modifiers. The symbols of modifiers and their meaning is shown
Additional Symbols
Datum
• It is a theoretically exact plane from which a dimensional measurement is made
• Datum system is a set of symbols which is used to describe the function and dimensions to the user
• Datum plane, Datum axis and Datum center plane are used to make measurements of a part
Datum symbols
Feature Control Frame
It is a rectangular box which is divided into compartments within which symbols, modifiers, tolerances, etc… are placed. Below is an example for feature control frame
GD&T in a part design (An example)
Thank you!!
(Referred from Wikipedia and concerned websites)