I Know Everything About GD&T Except - anida · PDF fileS s 5 4 4 Good Starting Position We...
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3DS.COM/SOLIDWORKS © Dassault Systèmes | Confidential Information | 2/10/2015 | ref.: 3DS_Document_2014 1 3DS.COM/SOLIDWORKS © Dassault Systèmes | Confidential Information | 2/10/2015 | ref.: 3DS_Document_2014 I Know Everything About GD&T Except… Thomas Allsup
Transcript of I Know Everything About GD&T Except - anida · PDF fileS s 5 4 4 Good Starting Position We...
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14 I Know Everything
About GD&T Except…
Thomas Allsup
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About the Presenter
Thomas Allsup
• Eighth time SWWorld Attendee
• Fifth time presenter
• Co-chair of North Texas SolidWorks Users Group
• BSME Oklahoma State University
• MSME University of Texas at Arlington
• Partner at Anida Technologies, L.P., a Dallas based engineering consulting company.
• GD&T Aficionado
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Languages
We Know Everything About …
• Learning a new language is hard enough without having to learn the rules and
the exceptions at the same time.
• All languages have rules and exceptions…
See Dick.
See Jane.
See Dick and Jane.
…except after C and sometimes Y
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Good Starting Position
We Know Everything About GD&T
• When I teach GD&T, especially to beginners, I try desperately to avoid talking
about the exceptions.
• This year we are starting with the idea that we all know all the GD&T rules.
• Now let’s screw everything up by reviewing the exceptions…
• Just like any language, there’s a lot of contradictions.
• Contradictions normally require memorization…
• There is not going to be a test at the end…
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Check the archives…
Previously at SolidWorks World...
• 2009 How to Spell GD&T
• Introduced FOPRL Chart
• 2010 The Revenge of the Circled Letters
• Modifiers
• 2013 Hitchhiker’s Guide to GD&T
• Tolerance Zones and Shapes
• 2014 The Big GD&T Theory
• Datums and Basic Dimensions
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Squirrel!
A Nice Flow of Information
• One of the hallmarks of a good presentation is a nice logical flow of information that builds from the first slide to the next.
• In fact, you will be asked at the end of this presentation to provide an evaluation using your mobile apps.
• Please be kind.
• This presentation is a list of exceptions to rules that defies logical grouping.
• In fact, I normally discourage questions until the end but please stop me as we go this morning.
• With those disclaimers, let’s get started…
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ASME Standard
There Can Be Only One…
• ASME Y14.5
• 1994?
• 2009?
• ISO1101?
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A Threat to the Standard?
IBR
• ASME is a Standards Development Organization (SDO)
• SDO’s develop “voluntary consensus standards”
• SDOs have substantial costs for developing and maintaining standards
• Currently revenues from the sales and licensing of copyrighted standards help fund SDOs (along with training and certification)
• If the IBR (Incorporated by Reference) – Code of Federal Regulations (CFR) lawsuit wins its appeals process then all the engineering standards will become public domain
• This will affect ASME (and IEEE and a multitude of other SDO’s) business model
• Good news is the standards might be free in the future
• Bad news is you get what you pay for…
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Reference to Gaging
• ASME Y14.5 is a drawing standard, not a gaging standard.
• Section 1.1.6 states that any gaging discussed is for illustration purposes only
• ASME Y14.43 Dimensioning and Tolerancing Principles for Gages and Fixtures
tells you how to make gages and fixtures
• ASME B89 is collection of metrology standards that tell you how to measure
• B89.3.1 Roundness
• B89.3.4 Axes of Rotation
• B89.3.7 Surface Plates
• B89.7.2 Measurement Planning
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Metric Units
1.1.2 “Metric units are expected to supersede Standard units”
• There is only three countries in the world that don’t use metric system.
• Extra points if you can name one country.
• Liberia, Myanmar and of course, the United States of America
• Thanks Jimmy Carter and his short lived “United States Metric Board”
• Interestingly the bill was signed by President Ford and unfunded under President Reagan.
• There are still a lot of engineering drawings that use inches.
• Use IN for the abbreviation of inches
• Use mm for millimeters
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Only Capital Letters
All notes, title block entries, dimensions only use capital letters
except
• Metric units which must use appropriate upper and lower case.
• “m” is milli or one thousandth
• “M” is Mega is 100,000X
• I have absolutely no idea how far a MM is? mm not MM
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Boundary
• Datums are theoretical so they don’t have physical size or “condition” so MMC,
LMC, and regardless of feature size were deemed inappropriate starting in 2009.
• Datums now have:
• Maximum Material Boundary (MMB)
• Least Material Boundary (LMB)
• Regardless of Material Boundary (RMB)
• I will probably never get used to calling datums MMB instead of MMC.
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SolidWorks World 2015 Obligatory SolidWorks Slide
• The concept of regardless of
feature size is still in the current
2009 standard.
• The symbol has not been
acceptable on drawings since 1994.
• So why is it still on symbol palette?
• In that same vein, why isn’t “I” and
“CF” isn’t on the palette?
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Definition of Tolerance Zone
3.6 Feature control frames are always total wide
tolerance unless….
• You add a diameter or spherical diameter symbol to
change the total wide to a cylindrical or spherical tolerance
zone.
• Maybe this causes a bad flashback to SWW 2013
Hitchhiker’s Guide to GD&T
• Tolerance Zones and Shapes
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Envelope Principal
2.7.1 Limits of size is first magnitude of control and is always in
effect except
This is sometimes called the first rule of GD&T – geometric controls are a
refinement of control.
• 2.7.1 Independent Modifier
• 2.72 Stock pieces
• 2.73 Free State Variation is applied
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Independent Example
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Stock Size
1.4(h) All dimensions have tolerances unless
identified as stock size.
• If you buy a
• 2 x 4 piece of wood
• 20 AWG wire
• 16 Ga sheet of steel
Then the size of the stock item and any expected
tolerances are defined by where you buy them!
Caveat emptor (Buyer Beware)
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Free State
All dimensions and tolerances apply in the free state condition except
• 4.20 Restrained Condition
• Heh heh heh - he said 420…
• 5.5 Free State Modifier
• You can’t restrain a part to measure it
• My apologies to Werner Heisenberg but
measuring something doesn’t necessarily
affect the measurement. F
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Tolerances Across Surface or Edge
You only measure the surface or edge of the part you wish to inspect
except
• 7.4.1 Projected Tolerance Zone
• Moves the tolerance inside the part to someplace off the part out in space - hence the name
Projected Tolerance Zone.
• Projected Tolerance Zone only works on the three orientation controls applied to a feature of
size and position.
• Tangent Plane
• You measure a gage block placed on the surface to measure instead of the surface itself.
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Projected Tolerance Example
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Tangent Plane
Example
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Tolerances Apply to Full Feature
1.4 (n) All tolerances apply for full depth, length, and width of the feature.
• Well except for four things:
• Between Symbol
• Limits where the tolerance starts and stops along a features length.
• All Around and All Over Leader Modifiers
• Extends tolerances to all the edges in a place or all over the part.
• Per Length or Per Area Controls
• Allows for more tolerances locally while limiting the overall tolerance
• Separate Features
• A disjointed surface can be treated as a single surface.
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Between Symbol Example
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All Around
Example
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All Over
Example
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Straightness Per Length Example
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Flatness per Area Example
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Separate Features
Continuous Features
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Symmetrical Outlines
• 1.8.9 Centerline not the same as GD&T control symmetry
• Incidentally, the symbol CL has been replaced with a “equal sign” on the center
line somewhere along the away.
• Imagine me saying in an old man voice “I don’t like that change”…
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Datum Feature Symbols
3.3.2 Use any letter except:
• I
• O
• Q
• I personally don’t like S or Z either but that’s for another day…
• If you run out of A through Z then you can use AA through AZ.
• I have friends who like “R” for runout datums and prefer “X-Y-Z” to “A-B-C”
• I might need new friends.
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Straightness of MMC
You can’t use modifiers on geometric form controls.
• Well except for straightness
• If it is applied to a feature of size
• Then you can use a MMC
• Section 5.4.1.2
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Straightness
at MMC Example
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SEP REQT
4.19 All feature control frames that have the same datums listed in
the same order with the same modifiers have meet there
requirements at the same time.
• That is unless you state a tolerance is a SEP REQT
• Huh?
• All this means is the inspector would normally require the same set-up and you
are allowing the part may be set-up in one or more means.
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Separate Requirements Example
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SIM REQT
Even if two or more feature control frames have different datums and
the same datums with different modifiers listed in a different order or
with the different modifiers, you can make the requirements at the
same time by stating it must be a SIM REQT.
• Huh?
• All this means is the inspection must be done from the same set-
up.
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Bidirectional
Tolerance Example
• All controls provide tolerances
that are equally disposed on both
sides of the nominal…
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Tolerances are Uniform, except…
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Datums Can’t Move
Datums are planes, axes, or boundaries and although they might be
stationary (MMC and LMC) or compliant (RFS) but they never, ever
move except…
• 4.11.10 Datum Translation
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Datum Translation Example
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Tolerances have to be listed in the FCF
Two weird exceptions to this rule
• Use a tabulated Tolerance Chart (TOL)
• Statistical Process Control (ST)
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Caliper Test for Features of Size
• Prior to 2009, anything you could measure with a pair of calipers was a feature of size.
• As long as it was two parallel surfaces (opposed or stepped), cylindrical or spherical surface.
• After 2009, anything you could measure with a pair of calipers was a feature of size.
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That’s All of Them…except I left off a bunch of minor weird exceptions
• 1.7.1 Can’t use a dimension line as a extension line except in some coordinate
dimensioning schemes.
• 1.8.16.2 Chamfered round holes
• 2.9 Screw threads use Pitch Diameter unless you state MAJOR or MINOR
diameter
• Many more that I couldn’t list…
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SWW2016
How’s this for an exception? • I never plan this far in advance but I know what I am going to talk about next year.
• The SolidWorks World 2016 GD&T presentation will be titled “How Do You Measure
that GD&T Control?”
• It seems every GD&T discussion I have now, devolves into a talk about inspection or
metrology.
• Metrology is the science of measurement.
• Look for it next year in …
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Questions?
• This presentation is available right now on our website at www.anidatech.com.
• It will be available on the SolidWorks World 2015 archives along with my vocals in a short while.
• Android users, please look for our Caliper Simulator App on the GooglePlay store – new GD&T apps are on their way shortly!
• Email – [email protected]
• Twitter - @anidatech
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3DS
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IDW
OR
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ref
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t_20
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