engr 22 lec 20 sp07 gdt 2 bonus tol

[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt1

Bruce Mayer, PE Engineering 22 – Engineering Design Graphics

Bruce Mayer, PELicensed Electrical & Mechanical Engineer

[email protected]

Engineering 22

GD&TGD&TBonus Bonus

ToleranceTolerance



Skill-Development GoalSkill-Development Goal

Learn How to Use the GD&T MMC to Avoid Inspection-Rejection of Entirely Functional Parts

Use AutoCAD to Construct GD&T Feature Control Frames



Recall Matl Condition ModifiersRecall Matl Condition Modifiers Maximum Material Condition (MMC)

• the condition in which a feature of size contains the maximum amount of material everywhere within the stated limits of size.

Least Material Condition (LMC)• the condition in which a feature of size

contains the least amount of material everywhere within the stated limits of size

Regardless of Feature Size (RFS)• indicates a geometric tolerance applies at

whatever size the part is produced

M

L

S



Material Condition UsageMaterial Condition Usage MMC

• usually when geometric tolerances are applied at MMC the function is assembly

LMC• function is usually to insure that a minimum

distance on a part is maintained

RFS – Default Condition• often specified to insure symmetrical

relationships

• No “Bonus Tolerance” allowed



GD&T TolerancesGD&T Tolerances

From ASME Y14.5M-1994• Some ACAD Features based on Y14.5-1982



MMC → Bonus Tolerance Maximum material condition for a HOLE

feature is the SMALLEST sized hole. Maximum material condition for a SHAFT

feature is the LARGEST shaft. The maximum material condition modifier in a

feature control frame means that the tolerance applies at max. material condition. • If the actual hole is LARGER than the smallest

allowable hole, a BONUS tolerance can be added to the stated tolerance value.



MMC Bonus Tolerance ExampleMMC Bonus Tolerance Example Condsider the

GD&T Spec’dPart At Right

In particularnote the SIZE,and POSITION TOLERANCE on the Hole• Ø = 0.50 ±0.003

• Ø-POSITION Tolerance = 0.010– Relative to BASIC Dims 2.00 & .75

• MMC ModifierPositionSymbol



MMC Bonus Tolerance contMMC Bonus Tolerance cont Then the Tolerance

Zone at MMCShown at Right

The actual center of the hole (axis) must lie in the round tolerance zone. The same tolerance is applied, regardless of the lateral direction.• i.e., The Tolerance Zone is Circular,

NOT Rectangular– Same tolerance at 0°, 45°, 90° Measurement angles



MMC Bonus Tolerance cont.2MMC Bonus Tolerance cont.2

Recall The GD&T Spec

This means that the tolerance is .010 if the hole size is the MMC size, or .497. If the hole is bigger, we get a bonus tolerance equal to the difference between the MMC size and the actual size.



Gage Fixture DesignGage Fixture Design As the Part Design

Engineer We find that Parts that FIT & WORK in the Assembly are Being REJECTED by RI (Receiving Inspection)• Discover that RI

does Not Understand “Bonus” Tolerances

To Avoid Scraping Good Parts, Work with a High precision Machine shop to make a Gage Fixture• Gage Pin Precisely

Located at (2, 0.75)

• Gage Pin Precisely Machined to Ø0.4965– A bit Less than Lo-Lim

on Hole-Size;i.e., at the MMC



Gage Fixture DesignGage Fixture Design Made from Hardened Tool Steel

Axis Walls Shifted by the Pythagorean XY distance equal to half the Tolerance Zone

3535500.02201.0 yx



Min-Hole Part Checked by GageMin-Hole Part Checked by Gage Put Small-Hole Part

in Gage Block

Expand Origin Area

The Perfect Part Just Fits over the Pin, and Clears the Walls by ½ the Positional Tol.Zoom In



Max-Hole Part Checked by GageMax-Hole Part Checked by Gage Put Large-Hole Part

in Gage Block; move it to Up & Rt Till it hits the Gage Pin

Expand Origin Area

Note How the Axis Wall Clearance has Expanded by 0.003• Thus the Hole-Ctr for

this LMC Part can be Misplaced by 0.008

Zoom In



MMC Bonus ToleranceMMC Bonus Tolerance

This means that the tolerance is .010 IF the hole size is at the MMC, or 0.497. If the hole is BIGGER, we get a BONUS tolerance equal to the difference between the MMC size and the actual size.

Read Carefully §10-17 thru §10-23 in Text Book

Actual Hole Size Bonus Tolerance Ø of Tol. Zone

Ø .497 (MMC) 0 .010

Ø .499 (.499 - .497 = .002) .002 (.010 + .002 = .012) .012

Ø .500 (.500 - .497 = .003) .003 (.010 + .003 = .013) .013

Ø .502 .005 .015

Ø .503 (LMC) .006 .016

Ø .504 ? ?REJECTED – Out of Spec

NOT to scale



GD&T Caveat → Use with CareGD&T Caveat → Use with Care

GDT is VERY Powerful, BUT…It can be Quite CONFUSING and ESOTERIC

Many Degreed Engineers, as well as Most Drafters/Designers (and Some Machinists) have only a Vague Notion About Meaning of GDT Symbols• MisApplication and Confusion-Induced

Delays are COMMON– e.g. Try asking what MMC or RFS means…



Go, NoGo, and Go-NoGo GagesGo, NoGo, and Go-NoGo Gages The Gage we

Designed is Necessary but NOT sufficient

i.e., if part does NOT fit the Gage, Then REJECT it

However if part DOES Fit, it COULD Still be BAD• e.g., If The hole is

LARGER than 0.503 it could easily fit the gage

Thus our Gage is a NoGo Instrument



Complete Go-NoGo GagingComplete Go-NoGo Gaging To Complete the

Gage Set, We need to design a Precision Gage-PIN to Test for OverSize Holes

This is Also a NoGo Gage• If the Pin FITS in the

Hole, Then it is REJECTED

Thus we have a GO When the Part• Fits in the Gage Block

(Position & Small Hole)

• Does NOT Fit the Pin (Large Hole)



GD&T In AutoCADGD&T In AutoCAD Now that We

Understand how to USE GD&T let’s APPLY it with ACAD

Let Dim & Tol Our Spacer Plate with Changes

• Width now 4.00 ±0.01

• Height now 1.50 +0.00/-0.02



All Done for TodayAll Done for Today

The AMEand

Bonus Tol.

If a hole, for instance, has the following size and geometric control, and the hole measures .502. It would be incorrect to use a bonus tolerance of .003 (.502 - .499(MMC)) if the hole is not perfectly oriented to the Datums. If the hole is out of perpendicular to datum A by .002, for instance, the bonus that may be used is reduced by that amount. The bonus would be merely .001 and the allowable position tolerance = .016.



Bruce Mayer, PELicensed Electrical & Mechanical Engineer

[email protected]

Engr/Math/Physics 25

AppendiAppendixx

6972 23 xxxxf



GDT Demo - 1 GDT Demo - 1

1. Open File• GDT_Demo_Lec-

19.dwg_Start.dwg

2. Set LtScale to 0.5

3. Set Snap to 0.0625”

4. Xline at Top Edge• Offset TWICE by

0.5

5. xLine at Lt Edge

• Offset by 0.5

6. Make Test-Dim to check Text-Height Relative to Part• Text & Arrows at Bit

Big

7. Make DimStyle half_3dec• Scale = 0.5

• Precision = 3-decimals



GDT Demo - 2GDT Demo - 2

8. Change to DimLayer and Dim Thickness at 0.5 offset xline

9. Use Line to Extend the 0.625 Dim-Ext_ln up to 1.0 offset

10.Open Geo Tol Dialog Box

• Dimension → Tolerance Menus

11.Use Dialog Box to Spec Flatness & Back Surface as the Datum



GDT Demo - 3GDT Demo - 3

12.Make DimStyle half_2dec_1side

13.Dim the 1.50 +0.00/-0.02 Hgt

14.Make DimStyle half_3dec_Basic

15.Apply Basic (boxed) Dims• 2.000

• 0.750



GDT Demo - 4 GDT Demo - 4

16.Make DimStyle half_2dec_2sided

17.Dim 4.00 ±0.01

18.Make DimStyle half_3dec_2sided_ManualDim Hole Dia.• 0.75 Above Top

Edge by Offset

19.Make Feature Control Frame (FCF) using PullDowns: Dimension → Tolerance

20.Manually position the FCF Below the Ø Symbol



GD&T Result w/ xLinesGD&T Result w/ xLines



GD&T Demo Final ResultGD&T Demo Final Result

engr 22 lec 20 sp07 gdt 2 bonus tol

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