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[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
Engineering 22
GD&TGD&TBonus Bonus
ToleranceTolerance
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt2
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt3
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt4
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt5
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
GD&T TolerancesGD&T Tolerances
From ASME Y14.5M-1994• Some ACAD Features based on Y14.5-1982
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt6
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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.
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt7
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt8
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt9
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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.
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt10
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt11
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt12
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt13
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt14
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt15
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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…
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt16
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt17
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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)
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt18
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt19
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt20
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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.
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt21
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
Bruce Mayer, PELicensed Electrical & Mechanical Engineer
Engr/Math/Physics 25
AppendiAppendixx
6972 23 xxxxf
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt22
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt23
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt24
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt25
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
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
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt26
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
GD&T Result w/ xLinesGD&T Result w/ xLines
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt27
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics
GD&T Demo Final ResultGD&T Demo Final Result
[email protected] • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt28
Bruce Mayer, PE Engineering 22 – Engineering Design Graphics