I Know Everything About GD&T Except… - anida tech

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3DS.COM/SOLIDWORKS © Dassault Systèmes | Confidential Information | 2/10/2015 | ref.: 3DS_Document_2014

I Know Everything About GD&T Except… Thomas Allsup


Thomas Allsup

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About the Presenter • 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


We Know Everything About …

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Languages • 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


We Know Everything About GD&T

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Good Starting Position • 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…


Previously at SolidWorks World...

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Check the archives… • 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


A Nice Flow of Information

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Squirrel! • 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…


There Can Be Only One…

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ASME Standard • ASME Y14.5 • 1994?

• 2009?

• ISO1101?


IBR A Threat to the Standard? 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… 8


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

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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


Only Capital Letters

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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


Boundary

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• 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.


SolidWorks World 2015

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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?


Definition of Tolerance Zone

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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


Envelope Principal

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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


Independent Example

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Stock Size

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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)


Free State

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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


Tolerances Across Surface or Edge

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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.


Projected Tolerance Example

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Tangent Plane Example


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. 22


Between Symbol Example

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All Around Example

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All Over Example


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

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• 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”…


Datum Feature Symbols

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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.


Straightness of MMC

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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


SEP REQT

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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.


Separate Requirements Example

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SIM REQT

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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 setup.


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Bidirectional Tolerance Example • All controls provide tolerances that are equally disposed on both sides of the nominal…


Tolerances are Uniform, except…

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Datums Can’t Move

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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


Datum Translation Example

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Tolerances have to be listed in the FCF

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Two weird exceptions to this rule • Use a tabulated Tolerance Chart (TOL)

• Statistical Process Control (ST)


Caliper Test for Features of Size

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• 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.


That’s All of Them…except

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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…


SWW2016

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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 …


Questions?

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• 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 • Instagram - @anidatech

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I Know Everything About GD&T Except… - anida tech

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