Viva LaPaloozagon

I am being deployed last minute to research metrology options for a purchase we need to make. I will be there tomorrow and Wednesday if anyone from here would like to meetup, maybe even see if we find some squirrel lasagna and side salad.

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Wes Cisco over 5 years ago
Here is the promised summary of the three GD&T focused sessions I attended at HxGN LIVE 2019:
ASME Standards Update and Overview of Y14.5-2018 - Fred Constantino @ASME & Rob Jensen @ Hexagon.
New GD&T Library for PC-DMIS v2019R2 and v2020R1 – Rob Jensen @ Hexagon.
Pc-Dmis Mathmatical Definition of Datum Features per ASME Y14.5 & Y14.5.1 - Dr. Daniel Wilcox @ Hexagon.

I have struggled to write this review. The subject mater is complex and not easily communicated without images. I am hesitant to take too liberal an approach to copy/paste from the standards and slide decks because I respect intellectual property and I believe professionals working in industry needing this information should purchase the standards. So I have tried to strike a balance by mentioning all of the key points from each presentation, but not trying to fully explain every concept. Overall I find this unsatisfactory, but it is the best I can do at this time and I do not want to keep putting off finishing this project.

ASME Standards Update:

ASME is focused on helping the global engineering community develop solutions to real world challenges. ASME was founded in 1880 to address issues with industrialization and mechanization, in particular boilers and pressure vessels that were exploding with alarming frequency. ASME seeks to achieve it’s goals primarily through the creation and revision of consensus based standards.
The Y14 group of standards, and in particular Y14.5 have proven to be extremely useful to industry and have been adopted widely. ASME has an official Spanish translation committee for several Y14 standards. ASME has agreements for the translation of Y14.5 into German, Japanese, Swedish, and Chinese (tentative). ASME offers GD&T Training and Certifications.
ASME is currently working hard to fill the gaps and develop the standards necessary for industry to complete the transition to model based definitions. There is a long way to go, but the future is in sight when 2D drawings will be as obsolete as a true “Blue Prints” are today. This transition was begun in Y14.5-2009 and has been expanded in Y14.5-2018.

An overview of Y14.5-2018:

Surface texture is included in conformance to tolerance now.

4.1 Fundamental Rules
(s) Unless otherwise specified, elements of a surface include surface texture and flaws (e.g. burrs and scratches). All elements of a surface shall be within the applicable specified tolerance zone boundaries.

Per ASME Y14.5-2009 the method of datum definition is 'Candidate Datum Set'. This method has a few flaws including:
Ambiguous coordinate systems
Impractical (almost never actually used)
Encourages form error
Undefined for multi-feature datums

So they have abandoned Candidate Datum Sets and started over. This is huge and fundamental. Going forward it should help reduce differences in results from various softwares and inspection methods (i.e. surface plate vs. CMM). The new method truly represents how parts assemble and fit to physical datum simulators.

In ASME Y14.5-2018 there is a new datum definition: 'Constrained Least Squares' (A.K.A. Constrained L2)

7.11.2 Irregularities on Datum Features Applicable RMB
If irregularities on a datum feature are such that the part is unstable (i.e. it rocks) when it is brought into contact with the corresponding true geometric counterpart, the default requirement is that the part be adjusted to a single solution that minimizes the separation between the feature and the true geometric counterpart per ASME Y14.5.1M. If a different procedure is desired (candidate datum set, Chebychev, least squares, translational least squares, etc.), it shall be specified.

This single solution is 'Constrained Least Squares'. The problem with plain least squares is that it yields solutions that are in part "in material". Constrained least squares achieves a similar minimizing of deviation from nominal while constraining the solution to being entirely external to the material.
Nonmandatory Appendix B of the draft of Y14.5.1 explains in detail the pros and cons of the various methods of datum definition.

ASME Y14.5 -2018 section 5.17 has introduced a Tangent Plane Modifier ( “T” in a circle) for when it is desired to control a tangent plane established by contracting points of a surface. The standard illustrates this with orientation tolerances, however it may also have applications using other geometric characteristic symbols such as runout and profile when it is applied to a planar feature.

ASME Y14.5-2018 has also introduced a new Dynamic Profile Tolerance Modifier (a triangle symbol). The function of the dynamic profile is to allow form to be controlled independent of size. The example given was the gas tank on a motorcycle, it is fairly easy to understand the form needs to be precisely controlled but the size can vary much more without detriment to function.

Concentricity and Symmetry have been removed. ***Vigorous Applause***
Position and Runout are the recommended geometric tolerance to use for these applications now.

An overview of Y14.5.1-2019*:
*currently a draft, intent is to publish in 2019, but it might be delayed to 2020 if rejected during the approval process.

First a few relevant bits many may not be aware of. The current revision of Y14.5.1 - the math standard was issued in 1994 and reaffirmed in 2012. It was the first attempt to mathematically define the principles Y14.5 is based upon. Ideally there would have been a new revision to accompany Y14.5-2009 within a few years. Instead the existing was reaffirmed in 2012. There was a draft for public review of the Y14.5.1 based on Y14.5-2009 issued in December of 2018, just a few months after ANSI approved Y14.5-2018.
The committees of Y14.5 & Y14.5.1 have tremendous overlap. So while the Y14.5.1. committee could not begin working from Y14.5-2018 until after it was published, they were aware of the changes it would encompass before they finished work on the revision in response to Y14.5-2009. They have managed to word the critical passages in such a way that while defaulting to the Y14.5-2009 definitions, there are also allowances for the Y14.5-2018 definitions.

2.1.1 Establishing Surface Points - this paragraph has been eliminated in light of surface texture now being included in tolerance conformance.

4.7.11 Alternate Stabilization Procedure
In accordance with ASME Y14.5-2009 the default stabilization procedure is per candidate datum sets. However ASME Y14.5-2009 does allow for different stabilization procedures to be specified. When a single solution that minimizes the separation between the features and the simulator is specified the default procedure is Constrained L2 for datum features of size and Constrained L2 applied to the external envelope for planar features.

New mathematical definitions for Actual Local Size:
Evaluation of Actual Local size now has two prescribed methods.

Opposed points – an actual local size exists for every line perpendicular to the local size spine at the point this line intersects the 2 dimensional local size spine.

Circular Elements – If actual local size is to be evaluated by the circular elements method, two actual local sizes exist for every point on the local size spine in the cross-section perpendicular to the local size spine at that point (cylindrical features of size); or every plane passing through the center point (spherical features of size). Where Rule 1 does not apply, both maximum material and least material local sizes are of interest. If Rule 1 applies, only the least material local size is of interest.

New Actual Value for Profile (bilateral tolerance): In the 1994 version two actual values, one for surface variations in the positive direction and one for the negative direction were calculated. For each direction, the actual value of profile is the smallest intermediate tolerance to which the surface conforms. The new Actual Value of a profile tolerance is based on an enveloping zone called the ‘actual zone’ that is generated in the same way as the tolerance zone.
I find this very difficult to describe at the level of the mathematical standard and will not attempt to explain it further here.

Lastly, the New GD&T stuff in Pc-Dmis.

Due to these changes there is a new GD&T library in v2019 R1 and there will be a new GD&T command in v2020 R1.
The goals for these changes are Accuracy, Reliability, Ease of Use, and Performance. To achieve these goals they have adopted a Test-driven development plan with emphasis on an automated test suite to ensure new changes don’t break old functionality. Additionally, they have sanity checked the new stuff against other software packages. There have been improvements to make it easier and more intuitive to use Pc-Dmis in compliance with the standards. Lastly there has been a strong focus on ensuring a smooth migration for routines from Xactmeasure to the new GD&T command.

V2019 R1 - New GD&T library:
Constructed Primary Datum Plane. This command replaces the High Point Plane from previous versions. Use this option to construct a primary datum plane per ASME y14.5 or ISO 5459. Input features can be:

Three or more of any feature type

Any single feature set

Any plane feature

Any scan

Constructed Secondary and Tertiary Datum Planes. Constructed Line and Constructed Point used for orientation constrained secondary and tertiary datum planes. Tertiary datum basic angle to secondary is variable (90 degrees is the default). This means you can finally, easily and correctly handle inclined datum features such as shown Y14.5-2009 fig 4-7.

Local Size Options – opposed points or circular elements.

V2020 R1 – New Geometric Tolerance Command:
Supports ASME Y14.5-2018
Supports ISO 1101:2012
Features:

Expanded Datum Definition Capabilities – Define a Common Datum (previously Multiple Datum Feature, often colloquially called Compound Datums) or a Single Datum from multiple features of size ( a hole pattern).

Supports Four Segment Composite Feature Control Frames. (5 is the max, but more than 4 is extremely rare). Analysis by Segment and Math option for Datums and Features of composite FCFs.

Intelligent Simultaneous Evaluation – Profile and Position.

That is all I have for now. I expect there will be questions aplenty. I will try to answer them as best I can, but please bear in mind I have limited time available for forum fun these days.

P.S. Look for a draft of Y14.45 to be available for public review later this year!
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dph51 over 5 years ago in reply to Wes Cisco

Thanks for sharing, Wes. Only question I have is, did they deal with the squirrel lasagna quandary?
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dph51 over 5 years ago in reply to Wes Cisco

Thanks for sharing, Wes. Only question I have is, did they deal with the squirrel lasagna quandary?
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