Support for a pattern/datum bonus value

[GitHubDaveSmith]

There has been a requirement for a second bonus value to be applied to a position characteristic. Note that this is different to the bonus value that is currently supported.

[daniel-campbell]

@bobstoneorigin thoughts on this?

[bobstoneorigin]

The use of a material modifier on datum can give a datum mobility in the context of a datum reference frame. Depending on the datum feature type the shape of the effective tolerance zone around the datum feature can be defined by a circle/cylinder/sphere/parallel planes. The size of this effective tolerance zone can be expressed as a simple number. The natural home for reporting such a number would be on a measured/actual datum or DRF with a name like or perhaps .

The difficulty is that whatever this number is called, it can't be simply added to the value of a feature/pattern tolerance zone in the same way as the bonus from the feature's own material condition modifier can be. While datum mobility increases the effective size of a tolerance zone at the feature, it can also change its shape depending on the relative location of the feature to mobile datums. The shape of the effective feature tolerance zone could remain roundish, or it could become bean-shaped. Furthermore, features nearer the mobile datums will have the effective size of their tolerance zones increased by a lesser amount than features farther away from the mobile datums. So boiling down datum mobility's effect on a feature's/pattern's tolerance zone is impossible to reduce to a simple number.

That said, QIF is just a data model, a set of data elements which is a union of the data elements necessary to capture the requirements and capabilities of several national and international standards, in house and public specifications, CAD systems, and varied measurement systems. So, if a number called "datum bonus" typically appears in a measurement report, we should make available a data element for its storage. For example:
<xs:element name="DatumBonus"
type="MeasuredLinearValueType"
minOccurs="0">
xs:annotation
xs:documentation
The optional DatumBonus element is the bonus from datum mobility from a report or an analysis.
</xs:documentation>
</xs:annotation>
</xs:element>

[daniel-campbell]

Dave, what do you mean by pattern bonus? The way I'm thinking about it now, a feature being part of a pattern adds contraints to the fit, but I don't think I understand your meaning

[GitHubDaveSmith]

Hi Daniel, Bob, I will have to ask the person who requested this change. I have been struggling to understand what this means myself. I will get back to you.

[larry-bergquist]

Chiming in support of Bob Stone's comments.

ASME Y14.5-2018 7.11.11 could be used for support of "Datum Feature Shift/Displacement", or datum refrence frame mobility, I have also heard people refer to this as the part ratteling around in the gage.

-2018 7.11.11 Datum Feature Shift/Displacement
MMB or LMB modifiers applied to the datum feature reference allow the datum feature to shift/displace from the boundary established by the true geometric counterpart in an amount that is equal to the difference between the applicable (unrelated or related) AME for MMB, actual minimum material envelope for LMB, or surface of the feature and the true geometric counterpart. The datum reference frame is established from the true geometric counterpart and not the datum features.

Additional comment:
Y14.5-2009, and -1994 support this concept. The wording has changed through the 3 releases as there was mis-application in industry. Much of the wording in -2009 was in attempt to improve the application and use of datum feature shift/displacement.
It is important to note the part shifts or displaces in the DRF. This may accept additional parts as a result of the shift.

-2018 7.11.3 Effect of Specified Material Boundary on Datum Feature References
The boundary applicable to datum features referenced in a feature control frame affects the relationship of the part to the datum reference frame. RMB is implied when no modifier is shown. MMB or LMB modifiers may be applied to any datum feature reference, except where the primary datum feature is planar.

There is not an additional (or bonus) tolerance applied to features or pattern of features where MMB or LMB modifiers are applied.

I suggest:
<xs:element name="DatumRefFrameShift" or "DRFShift"
This is consistent with recently published Y14.45-2021 Measurement Data Reporting
ref para. 11.4 DATUM REFERENCE FRAME SHIFT AND SIMULTANEOUS REQUIREMENTS
Fig.11-6 Example Data Report for Figure 11-5

I hope the references to ASME Y14.5-2018 is useful for this discussion.
Best Regards,
Larry

[GitHubDaveSmith]

Hi all, many thanks for your support with this issue. Having discussed this in a lot more detail with the individual who originally stated the reason for having a custom attribute describing what appears to be a second bonus value, the need for that attribute is now in doubt. I am happy to close this issue.

[daniel-campbell]

At the very least, it is good discussion. I think it is worth keeping open.

[larry-bergquist]

👍

…

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[GitHubDaveSmith]

Hi again, so with this issue having been left open I can now say with a lot more confidence what we were trying to achieve. The tolerance in question was a composite position tolerance (applied to a pattern of holes). What we would like to report is both a feature bonus and a pattern bonus. We would like to report these values separately understanding that one does not affect the other even though the values can often be the same. I note that Daniel asked what a 'pattern bonus' was. I have been advised that it would be the smallest bonus available within the collection of features that make up the pattern.