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Hi , Regarding parallelism . 1
- Thread starter Rwelch9
- Start date
Rwelch9,
Assuming from your previous posts you are going by Y14.5 then yes, it must be related to one or more datum features. From Y14.5-2009 para 6.4 (Y14.5-2018 para 9.3) Specifying Orientation Tolerances "When specifying an orientation tolerance, the considered feature shall be related to one or more datums."
What you are describing is "mutual" or "datumless" paralellism. Per the above this is explicitly no longer allowed in Y14.5 (it was in previous versions I believe).
Assuming from your previous posts you are going by Y14.5 then yes, it must be related to one or more datum features. From Y14.5-2009 para 6.4 (Y14.5-2018 para 9.3) Specifying Orientation Tolerances "When specifying an orientation tolerance, the considered feature shall be related to one or more datums."
What you are describing is "mutual" or "datumless" paralellism. Per the above this is explicitly no longer allowed in Y14.5 (it was in previous versions I believe).
- Thread starter
- #3
I can't speak to the committee's exact reason for specifically disallowing this practice.
Straightness or flatness (whether DML or elements) will not provide even a similar desired control as it will not limit taper. If you are looking to use +/- toleranced dimensions it tough to find a perfect analog to what you're looking for, at least not a non-controversial one.
Not a perfect solution but setting one side as a datum feature and holding parallelism of the other surface back to this established datum feature can be utilized.
If you can use basic dimensions and have the 2018 standard, a basic dimension with a multiple segment profile tolerance, with the lower segment having the translation modifier would provide mutual parallelism of the surfaces. A similar solution with creative use of composite tolerances could work as well. A +/- toleranced dimension with a 2X datumless profile tolerance with leaders attached to both surfaces could as well, but you may have some raise issues about that combination.
One of the more controversial solutions would also be to set the width of the feature of interest as your datum feature, and then apply parallelism tolerances of both surfaces back to this datum feature.
Of course, if you could hold the two parallel features back in orientation to a separate datum feature this would of course hold the two plane parallel with of course the caveat that they must be held in orientation to this other datum feature.
Straightness or flatness (whether DML or elements) will not provide even a similar desired control as it will not limit taper. If you are looking to use +/- toleranced dimensions it tough to find a perfect analog to what you're looking for, at least not a non-controversial one.
Not a perfect solution but setting one side as a datum feature and holding parallelism of the other surface back to this established datum feature can be utilized.
If you can use basic dimensions and have the 2018 standard, a basic dimension with a multiple segment profile tolerance, with the lower segment having the translation modifier would provide mutual parallelism of the surfaces. A similar solution with creative use of composite tolerances could work as well. A +/- toleranced dimension with a 2X datumless profile tolerance with leaders attached to both surfaces could as well, but you may have some raise issues about that combination.
One of the more controversial solutions would also be to set the width of the feature of interest as your datum feature, and then apply parallelism tolerances of both surfaces back to this datum feature.
Of course, if you could hold the two parallel features back in orientation to a separate datum feature this would of course hold the two plane parallel with of course the caveat that they must be held in orientation to this other datum feature.
greenimi,
I am mostly going off of an old conversation, specifically ( where CH on (24 May 18 13:48) refers to it as past practice. I am not sure when, but it seems like this may have been an accepted practice at one time. I don't have access to versions of Y14.5 prior to 1994 so I can confirm this.
I am mostly going off of an old conversation, specifically ( where CH on (24 May 18 13:48) refers to it as past practice. I am not sure when, but it seems like this may have been an accepted practice at one time. I don't have access to versions of Y14.5 prior to 1994 so I can confirm this.
greenimi,
That might be, however I assumed the first post (24 May 18 13:48) to refer to ASME and the one following it on (24 May 18 13:53) to refer to ISO. I have actually seen features that are contained in that post on an excerpt/page from a book that was based on ASME - albeit it was quite old. It would take me a while to find where it was from exactly.
That might be, however I assumed the first post (24 May 18 13:48) to refer to ASME and the one following it on (24 May 18 13:53) to refer to ISO. I have actually seen features that are contained in that post on an excerpt/page from a book that was based on ASME - albeit it was quite old. It would take me a while to find where it was from exactly.
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1
- #10
Because by default, if you want two surfaces to be parallel, one surface will have a "tolerance zone" within which all elements must lie, and the other will not.Rwelch9 said:
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
pmarc
Mechanical
- Sep 2, 2008
- 3,248
Just like there are examples in the standard of valid datumless position tolerance applications, theoretically the datumless parallelism tolerance (or any other orientation tolerance) could also work.
The concept has been brought to Y14.5 committee's attention in one of the recent ASME meetings.
The concept has been brought to Y14.5 committee's attention in one of the recent ASME meetings.
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