Engineering 22
GD&T
Bonus
Tolerance
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
BMayer@ChabotCollege.edu
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Skill-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
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Recall Matl Condition Modifiers
 Maximum Material Condition (MMC) M
• 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) L
• 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) S
• indicates a geometric tolerance applies at
whatever size the part is produced
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Material 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
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
GD&T Tolerances
 From ASME Y14.5M-1994
• Some ACAD Features based on Y14.5-1982
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
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.
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
MMC Bonus Tolerance Example
 Condsider the
GD&T Spec’d
Part At Right
 In particular
note 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 Modifier
Engineering 22 – Engineering Design Graphics
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Position
Symbol
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
MMC Bonus Tolerance cont
 Then the Tolerance
Zone at MMC
Shown 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
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
MMC 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.
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Gage 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
Engineering 22 – Engineering Design Graphics
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 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
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Gage Fixture Design
 Made from Hardened Tool Steel
 Axis Walls Shifted by the Pythagorean XY
distance equal to half the Tolerance Zone
x  y  0.01 2
Engineering 22 – Engineering Design Graphics
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2  0.0035355
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Min-Hole Part Checked by Gage
 Put Small-Hole Part
in Gage Block
Zoom In
 Expand Origin Area
Engineering 22 – Engineering Design Graphics
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 The Perfect Part
Just Fits over the
Pin, and Clears the
Walls by ½ the
Positional Tol.
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Max-Hole Part Checked by Gage
 Put Large-Hole Part
in Gage Block; move
it to Up & Rt Till it hits
the Gage Pin
Zoom In
 Expand Origin Area
Engineering 22 – Engineering Design Graphics
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 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
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
MMC 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
Actual Hole Size
size and the
Ø .497 (MMC)
actual size.
Ø .499
NOT to scale
0
.010
(.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
?
Engineering 22 – Engineering Design Graphics
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Ø of Tol. Zone
.002
(.499 - .497 = .002)
Read Carefully
§10-17 thru
§10-23 in Text
Book
Bonus Tolerance
REJECTED – Out
? of Spec
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
GD&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…
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Go, 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
Engineering 22 – Engineering Design Graphics
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 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
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Complete 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)
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
GD&T In AutoCAD
 Now that We
Understand how to
USE GD&T let’s
APPLY it with ACAD
• Width now 4.00
±0.01
• Height now 1.50
+0.00/-0.02
 Let Dim & Tol Our
Spacer Plate with
Changes
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
All Done for Today
The AME
and
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.
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Engr/Math/Physics 25
Appendix
f x   2 x  7 x 
9x  6
3
2
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
BMayer@ChabotCollege.edu
Engineering 22 – Engineering Design Graphics
21
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
GDT Demo - 1
1. Open File
•
GDT_Demo_Lec19.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
Engineering 22 – Engineering Design Graphics
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•
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 = 3decimals
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
GDT Demo - 2
8. Change to
DimLayer and Dim
Thickness at 0.5
offset xline
9. Use Line to Extend
the 0.625 DimExt_ln up to 1.0
offset
•
Dimension →
Tolerance Menus
11. Use Dialog Box to
Spec Flatness &
Back Surface as
the Datum
10. Open Geo Tol
Dialog Box
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
GDT 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
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
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
Engineering 22 – Engineering Design Graphics
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19. Make Feature
Control Frame
(FCF) using
PullDowns:
Dimension →
Tolerance
20. Manually position
the FCF Below the
Ø Symbol
Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
GD&T Result w/ xLines
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
GD&T Demo Final Result
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt
Engineering 22 – Engineering Design Graphics
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Bruce Mayer, PE
BMayer@ChabotCollege.edu • ENGR-22_Lec-19_GDT_Bonus-Tol-1.ppt