Overview of Critical Changes to

ASME and ISO GD&T Standards

Rob Jensen, Dimensional Standards Compliance Manager

13, June, 2018

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1. Overview of Critical Changes to ASME and ISO GD&T Standards

a) ASME

i. Y14.5 - DRAFT Dimensioning and Tolerancing (publication in 2019)

ii. Y14.5.1 - DRAFT Mathematical Definition of Dimensioning and Tolerancing Principles (publication in 2019)

b) ISO

i. ISO 1101:2017 - Tolerances of form, orientation, location and run-out (published)

ii. ISO 5459 - DRAFT - Datums and datum systems (publication in 2019)

2. PC-DMIS GD&T Enhancements

a) Versions 2018 -2019

3. Impact to industry

a) Investment and benefits

Agenda

ASME Y14.5 DRAFT (publication in 2019)

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ASME Y14.5 Draft – Surface Texture included in conformance to tolerance

ASME Y14.5 - DRAFT

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

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ASME Y14.5 – 2009 - Default is Candidate Datum Set

ASME Y14.5 - 2009

4.11.2 Irregularities on Datum Features

If irregularities on a datum feature are such that the part is

unstable (that is, it rocks) when brought into contact with the

corresponding datum feature simulator, the default

stabilization procedure is per candidate datum set as

outlined in ASME Y14.5.1M. If a different procedure is

desired (Chebyshev, least squares, translated least squares,

ect.), it must be specified

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ASME Y14.5 DRAFT - New default is single stable datum (constrained L2)

ASME Y14.5 DRAFT - 2019

7.11.2 Irregularities on Datum Features Applicable RMB

If irregularities on a datum feature are such that the part is

unstable (that is, it rocks) when brought into contact with the

corresponding true geometric counterpart, the default

requirement is that the part be adjusted to a single solution

that minimized the separation between the feature and the true

geometric counterpart per ASME Y14.5.1. If a different

procedure is desired (candidate datum set, Chebyshev, least

squares, translational least squares, etc.) it must be specified.

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New Dynamic Profile Tolerance Modifier

Dynamic Profile Tolerance Modifier

By default, a profile tolerance zone follows the true profile of the

considered feature. A profile tolerance zone is static and controls

both the form and size of the considered feature unless the dynamic

profile tolerance modifier is applied. Where it is desirable to refine

the form but not the size of a considered feature which is controlled

by a profile tolerance, the dynamic profile tolerance modifier , , may

be applied to a refining profile tolerance. The function of the dynamic

profile is to allow form to be controlled independent of size.

➢ Note: The dynamic profile modifier can also be used to control

form, orientation and location when referencing Datum(s). See

Y14.5 for complete definition of the dynamic profile tolerance

modifier.

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Concentricity and Symmetry have been removed from Y14.5

• Both Concentricity and Symmetry have been removed from Y14.5. Position and Runout are the recommended geometric

tolerances to use for these applications.

ASME Y14.5.1 DRAFT (publish in 2019)

Supports ASME Y14.5 - 2009

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Y14.5.1M – 1994 Y14.5.1 DRAFT 2019

ASME Y14.5.1 DRAFT – Removed section 2.1.1 Establishing the Surface Points

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ASME Y14.5.1 DRAFT – Alternate Stabilization Procedures

4.7.11 Alternate Stabilization Procedure

In accordance with ASME Y14.5 – 2009, if irregularities on a datum feature are such that the part is unstable when brought

into contact with the corresponding datum feature simulator, the default stabilization procedure is per candidate datum set as

outlined in this Standard. 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 datum features.

The background and details of this procedure can be found in the Nonmandatory Appendix B: Mathematical Datum

Simulators Referenced at RMB: Definitions and Properties.

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ASME Y14.5.1 DRAFT - New mathematical definitions for Actual Local Size

Evaluation of Actual Local Size (Opposing Points)

If actual local size is to be evaluated by the “two-point method” 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 (parallel plane features of size); every line passing through the local size spine (cylindrical features of size); or every line passing through the center point (spherical features of size). These lines are referred to as evaluation lines. See Fig. 2-5 for a graphical representation of the actual local sizes on a cylindrical feature.

Evaluation of Actual Local Size (Circular Elements)

If actual local size is to be evaluated by “circular elements, 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

• Cross-sections are formed by using a cutting pane for cylindrical and spherical features of size.

• Circular element actual local size is not defined for parallel planes features of size.

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ASME Y14.5.1 DRAFT - Revised actual value definition for Profile

The actual value for a profile tolerance for a single feature is the value of t0 + 2𝑔 for the envelope

zone to which the actual surface will conform.

Note: This applies to equally disposed, unequally disposed and unilateral profile tolerance zones.

Refer to Y14.5.1 for complete definition.

ISO 1101:2017 - Published

Focus on workflow

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New Modifiers for Toleranced features and Referenced features

Associated toleranced feature

• C Minimax (Chebyshev) feature

• G Least square (Gaussian) feature

• N Minimum circumscribed feature

• T Tangent feature

• X Maximum inscribed feature

Only used for tolerances that reference datums (orientation and location specifications)

Reference feature association

• C Minimax feature without constraint

• CE Minimax feature with external material constraint

• CI Minimax feature with internal material constraint

• G Least squares feature without constraint

• GE Least squares feature with external material constraint

• GI Least squares feature with internal material constraint

• N Minimum circumscribed feature

• X Maximum inscribed feature

By default, the reference feature association is the minimax (Chebyshev) association without constraint for form tolerances.

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Profile UZ modifier

ISO 5459 DRAFT (publish in 2019)

Supports ISO 1101:2017

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ISO 5459: 2011 default math is constrained Chebyshev (min/max)

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ISO 5459 Draft - New Default is Constrained L2

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Datums

PC-DMIS GD&T Enhancements

Versions 2018 - 2019

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New FCF Dialog Window – version 2018 R2

• Smaller dialog window

consumes less space in

Graphic Display Window.

• Replaced Advanced tab

with Reporting and

Nominals tabs.

• FCF and Datum Definition

dialog windows are

resizable to accommodate

long feature lists.

• Improved FCF editor

design with new icons for

adding or defining datums

and adding second single

segment or composite FCF.

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Use this option to construct a plane tangent to the peaks (or high points) on a surface. This command replaces the High Point Plane from

previous versions.

The input features can be:

• Three or more of any feature type

• Any single feature set

• Any plane feature (example shown below)

• Any scan

Constructed Tangent Plane

Tangent Plane Least Squares Plane

Nominal Plane

Actual Surface

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Three Math Types are available:

• Constrained L1

• L1 behaves somewhat like how a part would rest on

a surface plate under the influence of gravity, but it

does not handle rocker conditions gracefully. A

rocker condition is when a part might rock on a

surface plate instead of having obvious stable

contact points. A convex datum plane results in

a rocker condition. This method is essentially the

previous High Point Plane method (v2016).

• Constrained L2 (default)

• L2 performs much like L1 in many cases, but in rocker conditions, it always gives an

equalized solution. This is the recommended norm for Primary datums per ASME

Y14.5 DRAFT and ISO 5459 DRAFT.

• Constrained MinMax

• Usually gives a result controlled by the edges of the part. This may make it

undesirable in many cases. Use for Primary datums per ISO 5459:2011.

See the Help File for a more detailed description of the math types.

Version Migration: The High Point Plane constructed feature from previous versions of PC-DMIS

becomes a Tangent Plane constructed feature using the L1 math.

Constructed Tangent Plane

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Constructed Secondary and Tertiary Datum Planes – version 2019 R1

• Constructed Line and constructed Point used for orientation constrained secondary and tertiary datum planes. Tertiary

datum basic angle to secondary is variable.

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Constructed Secondary and Tertiary Datum Planes – version 2019 R1

High point - Tertiary

Tangent Line - Secondary

Tangent Plane - Primary

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ASME Local Size – Local Size options – version 2019 R1

• Size Dimension

• Add: Local Size Options

• Opposed Points

• Circular Element

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GD&T enhancements for 2019 R2

• ASME Y14.5 2019

• New math for datum features (constrained L2, constrained min/max and least squares)

• Orientation and location constrained datum reference frames

• Support for Translation modifier

• Profile - Single Actual value

• Math options for toleranced features (maximum inscribed, minimum circumscribed, least squares, constrained least squares)

• ISO 1101:2017

• New math for datum features (constrained L2, constrained min/max and least squares)

• Orientation and location constrained datum reference frames

• Support for DF (Distance Fixed) and DV (Distance variable) modifiers

• Profile with UZ modifier

• Math options for toleranced features (maximum inscribed, minimum circumscribed, least squares, constrained least squares)

What is the Impact to Industry?

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Impact to Industry

Investment:

• Software companies need to update math to comply with revised ASME and ISO Standards

• Industry needs to update software to comply with revised ASME and ISO Standards

• Industry needs training to understand and apply changes in ASME and ISO Standards

• NIST and PTB need to provide certification for new math algorithms as per ASME and ISO Standards

Benefits:

• Metrology software can be certified by NIST and PTB for:

• Datum features

• Features of size

• Geometric tolerances

• Correlation between customers and suppliers will improve significantly

• Improved correlation between different brand metrology software (reduced measurement uncertainty)

• Improved correlation between metrology software and conventional inspection (surface plate, hand tools and gages).

• Improved ability to estimate measurement uncertainty.

THANK YOU