Introduction to GD&T Session 2: Rules and Concepts of GD&T An exploration of the language known as Geometric Dimensioning and Tolerancing
Instructor: John-Paul Belanger
Review Benefits of GD&T The GD&T standard: ASME Y14.5-2009 Features: Surfaces vs. features of size Actual local size vs. mating envelope Basic dimensions
Today s Agenda The feature control frame Maximum Material Condition Least Material Condition Regardless of Feature Size Rule #2 Datums Datum precedence Datum targets Wrap-up
The Feature Control Frame 0.25 J
A Previous Example
Other Examples
Other Examples
Maximum Material Condition (MMC) Ext. feature: largest size Int. feature: smallest size 15.3
Least Material Condition (LMC) Ext. feature: smallest size Int. feature: largest size 14.7
Using the M Modifier Only a hole made at MMC must be within the 0.4
Still Two Things to Measure Actual Size Stated Geo Tol Bonus Tol MMC act. size Total Geo Tol (stated geo tol + bonus tol) Inner Boundary (size total geo tol) 17.9 0.4 0 0.4 17.5 18.0 0.4 0.1 0.5 17.5 18.1 0.4 0.2 0.6 17.5 18.2 0.4 0.3 0.7 17.5 18.3 0.4 0.4 0.8 17.5 18.4 0.4 0.5 0.9 17.5 18.5 0.4 0.6 1.0 17.5
MMC Modifier Often Helps! Allows a fixed-size functional gage Reduces scrap rate Ensures assembly Saves $
With the L Modifier Only a hole made at LMC must be within the 0.4 L
If the L Modifier Is Used Actual Size Stated Geo Tol Bonus Tol LMC act. size Total Geo Tol (stated geo tol + bonus tol) Outer Boundary (size + total geo tol) 18.5 0.4 0 0.4 18.9 18.4 0.4 0.1 0.5 18.9 18.3 0.4 0.2 0.6 18.9 18.2 0.4 0.3 0.7 18.9 18.1 0.4 0.4 0.8 18.9 18.0 0.4 0.5 0.9 18.9 17.9 0.4 0.6 1.0 18.9
Rule #2 First, a definition: RFS stands for regardless of feature size Now, the rule: Unless the MMC or LMC modifier is given, assume that a geometric tolerance (and any datum references) are RFS. Constant tolerance of 0.1 -- RFS
Datums Origin for a measurement From where does a location, orientation, runout, or profile dimension originate? 85 ± 0.4
Datums Definition: A theoretically exact point, axis, or plane that serves as the origin from which a measurement is made. Also: A datum feature is the physical surface used to create the datum.
Datums Datums are the key to consistency: Product Design Process Design Manufacturing Inspection
Symbol (Triangle may be filled or unfilled) (Old datum feature symbol)
Datum vs. Datum Feature atum plane A datum feature A
Selecting Datums The most important consideration is part / product What features on the detail orient and locate it in the assembly?
Selecting Datums Other concerns: Accessibility for mfg. and inspection Repeatability Stability Cost Time
Easy: A Single Datum
More Common: Two or Three Three mutually perpendicular planes: 1. Primary 2. Secondary 3. Tertiary T S P
First Plane Primary datum plane: Requires points of contact (min)
Second Plane Secondary datum plane: Requires points of contact (min)
Third Plane Tertiary datum plane: Requires point of contact (min)
Restricting Degrees of Freedom One plane, one hole, one slot: 1. Primary 2. Secondary 3. Tertiary
Restricting Degrees of Freedom One plane, one hole, one slot: 1. Primary 2. Secondary 3. Tertiary
Restricting Degrees of Freedom One plane, one hole pattern: 1. Primary - 3 degrees of freedom 2. Secondary - 3 degrees of freedom
Polling Question #3 What is the maximum number of datums allowed on a print? a. 1 b. 2 c. 3 d. 23 e. There is no maximum
Surface vs. FOS Datum
Surface vs. FOS Datum
Surface and FOS
M on a Datum Reference The geometric tolerance starts at 0.2, but can be fudged by 2 modifiers: Ø 0.2 stated tolerance + Ø 0.8 potential bonus tolerance + Ø 0.3 potential shift tolerance Ø 1.3 max. effective position variation
Shift vs. Bonus
Multiple Datum Features
Multiple Datum Features
Datum Targets A datum target is a way to identify specific points lines areas which are then used to establish the true datum. Good for unusual-shaped parts, or if the function dictates that only a portion of the surface will be contacted.
Datum Targets A Ø15 A1 Ø15 A2 Ø15 A3
Datum Target Simulator
Datum Targets
Datum Targets
Datums -- Summary
Q&A Please type any questions you have into the Q&A panel on your screen. Thank you!
Questions? If you would like to learn more, please contact: Tooling U-SME 866.706.8665 www.toolingu.com/ilt John-Paul Belanger 248.652.1397 belanger@gdtseminars.com