Dimensioning and Tolerancing Symbology Chapter 2 Dimensioning and Tolerancing Symbology

Objectives Identify and draw general dimensioning symbols and show their general applications. Identify and draw tolerancing symbols and show their general applications. Complete a feature control frame using the correct order of segments in the frame. Identify basic dimensions and define means for indicating a basic dimension on a drawing or in a design model.

General Dimensioning Symbols

Features of Size Regular features of size Irregular features of size Thickness Width Length Diameter Irregular features of size Enclosed shape Collection of features

Symbol Application Most symbols precede values Symbols preferred over abbreviations Symbol size relative to character height

Diameter

Spherical Diameter

Radius and Controlled Radius

Spherical Radius

Counterbore and Depth

Spotface

Countersink

Geometric Tolerancing Symbols Tolerances define allowable variation Variation occurs in every part Each tolerancing symbol shape reflects its purpose

Reference Value Dimension enclosed in parenthesis Related symbols are also enclosed

Geometric Tolerance Categories Form Orientation Profile Runout Location

Form

Orientation

Profile

Runout

Location Tolerance

New Modifiers Least material boundary (LMB) Maximum material boundary (MMB) Regardless of material boundary (RMB)

Feature Control Frame

Feature Control Frame Application On surfaces On features of size On threads

Datum Identification Datum feature Datum feature symbol Datum target symbol Datum reference frame

Datum Feature Symbol Application

Datum Target Symbol Used to identify datum target Identifying letter and number in lower half Target area size in top half Movable datum target symbol

Datum Targets

Basic Dimensions Tolerance shown in feature control frame Rectangle around dimension Basic dimensions may be identified by a note

ALL DIMENSIONS ARE BASIC or ALL UNTOLERANCED DIMENSIONS ARE BASIC Basic Dimension Notes ALL DIMENSIONS ARE BASIC or ALL UNTOLERANCED DIMENSIONS ARE BASIC

Past Practices