This can be done with shims on a surface plate or with an official algorithm further outlined in ASME Y14.5.1 Mathematical Definitions of Dimensioning and Tolerancing Principles to be released at the end of 2019. The 2018 version is now using a default stabilized single solution: “the part is to be adjusted to a single solution that minimizes the separation between the feature and the true geometric counterpart”. In previous versions of Y14.5, the standard used the candidate datum set to derive multiple permissible datums (find the datum that works). This applies to a planar datum feature or a datum feature of size referenced at RMB. The biggest change in the standard relates to the establishment of a datum from a datum feature that is unstable (i.e. So now in addition to being, in my mind, problematic from a practical standpoint for the reasons I previously stated (ie: without direct probing of the datum feature or some other time consuming stabilization/orientation procedure) we now have a specification which is ambiguous in what exactly it means by "minimum separation." As I often find myself wondering, I question what exactly the committee was thinking when adding this requirement. The actual text reads: "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" - pointing us to Y14.5.1 which only specifies a method to determine the candidate datum set, not to evaluate the new "minimum separation" requirement. As with many things, Y14.5 specifies something which looks intuitive enough on the surface (see definition of local size) which is actually ambiguous. RE: ASME Y14.5 technical question pylfrm (Mechanical) 17 Sep 19 02:47ĭoes it clarify whether the separation to be minimized is the maximum separation (distance) at any single location, the total separation (volume) over the entire feature, or perhaps something else? I would say probably without directly probing the datum feature it would be difficult and time consuming.Įvan says "How often do you see a part rocked to an optimal orientation on a surface plate during inspection?" and he's probably right that its not a regular occurrence, but at the same time how do we know however it was set on the surface plate is the "single solution"? At least per 2009 it was not difficult to be reasonably sure that it represented a valid candidate datum - now according to the letter of the standard in 2018 there is only one correct orientation. However if it is instead being put on a surface plate or other gauging surface instead of being directly probed, I wonder how it is expected that the inspector guarantees the proper single solution has been achieved.
#Is asme y14.5 a software software#
Whether most software isn't setup to attempt to choose other candidate datum planes if the feature(s) don't pass I don't know. So if the datum feature itself is being probed and the datum plane is being established virtually then likely nothing much changes from current practice - it makes sense that the software would choose the single solution which minimizes separation by default.
Hmm the more I think about this the more problematic it becomes. There are definitely some practical implications (unintended consequences?) associated with the new default How the inspector knows that the proper single solution has been achieved is another question entirely. RE: ASME Y14.5 technical question chez311 (Automotive) 16 Sep 19 20:35 There are definitely some practical implications (unintended consequences?) associated with the new default - these are going to be discussed and debated for the next few years, I'm sure. "With the new default of a single solution that minimizes the separation between the feature and the true geometric counterpart, the inspector is no longer allowed to wiggle the part on the gage. When a part is CMM inspected, the software rarely/never tries different candidate primary datum planes." How often do you see a part rocked to an optimal orientation on a surface plate during inspection? I haven't seen that very much. I suppose that this depends on how often candidate datums on a rocking primary datum feature actually come into play.
" The new stabilization default for RMB datum features will have some impact, but I'm not sure how much. Two quotes from experts (Evan J) might be helpful (I personally like these explanations) The differences between the two procedures (candidate datum set -default in 2009- versus single solution to minimize the separation -default in 2018 - has been discussed (at least tangentially) here:
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