Fig 7-39/2018 question 1

[greenimi]

In fig 7-39/ ASME Y14.5-2018

I think we all agree that the two bores should be “squiggly” (in the same way the outside diameter is shown a little “bumpy”), but my question is:
Do you think the correct way is to show the two (“squiggly” to be) holes slightly rotated clockwise? (my red adjustements)

I am comparing 7-38 with 7-39 and I am wondering why the holes in 7-39 are not rotated? Should they be? Shouldn’t they be?
Fig 7-38 looks okay, but if the intent is to show the same part on both scenarios (with and without the translation modifier) then why 7-39 does not show rotated holes?

 

[Burunduk]

Who is Pat McCuistion?

 

[greenimi]

Who is Pat McCuistion?

See the standard SUBCOMMITTEE 5 — DIMENSIONING AND TOLERANCING

 

[SeasonLee]

greenimi

Take a look at Y14.5.1-2019





Season

 

[greenimi]

The 4-32 subfigures are of two different parts. I have overlayed them below. View attachment 4572

3DDave,

Ok. Let's PRETEND they are the same part.
Do you agree then that the holes should be rotated?

 

[3DDave]

Any one part should be inspected in only one way.

If the holes were shown rotated the figures would be labeled:

"This part passes using this datum reference set"
and
"The same part fails using this datum reference set."

but I am not sure I see an advantage to that as there are a very large number of ways to fail/reject a part and a relatively small number of ways to accept one.

Concentration should be on understanding how datum references reflect the way the part interacts with the other parts or elements of the visible universe. My preference has been to give priority to currently manufactured items and assemblies and how they fit together and work.

 

[pmarc]

pmarc,

I agree with you, but now looking at the figures equivalent from 2009, I hope you agree with me that the figures 7-38 and 7-39 / 2018 were COPIED (or kept unaltered) from figures 4-32 a.) and b.) / 2009

So, in 2009 was just ONE figure (with 2 subfigures “so to speak”, subfigure a and subfigure b)). For me, regarding 2009 standard, it is clear that the intent was to use the same “as made”/ “as produced” part in relation with two DRF’s.

Since the figures were kept unchanged when the transition to 2018 occurred then I would “safely and reasonable” assume that the INTENT stayed the same (namely here to use the same “as produced” parts in two scenarios). When Pat McCuistion draw those figures I don’t think his intent was to change anything or use two sets of “as made” parts in 2018 figures. He just changed the titles (figures were renamed, naming from datum feature simulator to TGC), but not the concept.

Do you agree with my assessment? (I don’t have proof, facts and evidence, just using my logical –or not so logical thinking, how much I still have left)

Sorry greenimi, but I see no point in beating this horse any further, just like I don't understand why Pat's name had to be mentioned in the conversation.

Anyway, no matter what I think, all you said above is just a guess. An argument against your reasoning may be that there are multiple figures in the standard (both 2009 and 2018) that use the exact same approach as used in figs. 7-38 and 7-39. To name a few from the 2018: 7-20, 7-34 vs. 7-35, 7-36 vs. 7-37.

My opinion is that showing the holes/axes properly rotated in all these figures could have been easily done without even explicitly discussing this. Like I already said, it would be a nice feature for educational purposes, because not only would the difference in the simulators be shown, but also the effect of the difference on the toleranced features would be visualized. But again, this is just an opinion, which, as clearly shown by this thread, is not necessarily shared.

 

[greenimi]

Any one part should be inspected in only one way.

If the holes were shown rotated the figures would be labeled:

"This part passes using this datum reference set"
and
"The same part fails using this datum reference set."

but I am not sure I see an advantage to that as there are a very large number of ways to fail/reject a part and a relatively small number of ways to accept one.

Concentration should be on understanding how datum references reflect the way the part interacts with the other parts or elements of the visible universe. My preference has been to give priority to currently manufactured items and assemblies and how they fit together and work.

Interesting assessment about inspection methods.

By the same token, let me ask: Do you think that the SAME part could be okay per one specification (fig 4-32 b with translation), but not be good per the other specification (fig 4-32 a, without translation)?

Or maybe vice versa? (be good per 4-32 a, but be bad per 4-32 b)

 

[greenimi]

Sorry greenimi, but I see no point in beating this horse any further, just like I don't understand why Pat's name had to be mentioned in the conversation.

I agree, I should not have. I apologize for that. My point was (and is still is) that only one person is taking care of the entire set of figures from Y14.5 for each version release- and there are plenty of figures. No wonder some of the “details” have been missed. For me, those are not really small “details” / facts and ARE essential parts for the proper education and understanding.

 

[3DDave]

Interesting assessment about inspection methods.

By the same token, let me ask: Do you think that the SAME part could be okay per one specification (fig 4-32 b with translation), but not be good per the other specification (fig 4-32 a, without translation)?

Or maybe vice versa? (be good per 4-32 a, but be bad per 4-32 b)

Obviously, but if the mating part(s) don't allow for it there's no ability to do that. Similar results to just increasing the position tolerances to accept more poorly controlled parts. The goal isn't to accept parts but to accurately reflect the limitations allocated to the part within the context of some use. If the allocation was done correctly then changing the datum references will accept unusable parts.

 

[3DDave]

For me the largest problem to the way the diagrams are managed is their text is not searchable. After that is the lack of anyone giving them a critical review to ensure the details are as they should be. They look like they are taken through a translator to remove font references and replace the rendered glyphs with filled shapes; that removes the font dependency but also searchability. There is also something wrong with whatever the originating software is. All the arrowheads are borked. It's a small detail, but a trivial one to do correctly and it isn't. The line ends a joins got fixed in 2018, so that's an improvement.

Honestly I hate making diagrams and it's wonderful that Pat does this, but there are gaps in the system that is responsible for putting them into the standard without fixing some obvious errors, much less any subtle ones.

 

[greenimi]

Based on the figure posted by SeasonLee figure 4-4 / ASME Y14.5.1-2019:

IF I am going to force the red line to overlap with the blue line (which, probably, basically is getting rid of the translation modifier TRM) and making the tertiary datum feature simulator basically located and oriented (not just oriented) to the higher precedence datums are my following assessments correct:

- There are “as produced” holes that meet translation modifier DRF |A|B|C TRM|, but do not meet |A|B|C|
- There are “as made” holes that do not meet |A|B|C TRM| DRF, but meet |A|B|C| DRF.

Which one of my assessments above would you say it is true and more importantly why? I am just trying to understand their usage correctly and their relationship, if any.

 

[3DDave]

The 14.5.1 figure doesn't make sense. The datum feature is allowed to translate rather than imposing a rotation.

The true positions of the holes remain aligned with the axis established by datum feature B and the midplane of C remains perpendicular to the co-planar axes of the three circular features. The fixture would not allow the simulator for C to rotate relative to the holes.

 

[greenimi]

The 14.5.1 figure doesn't make sense. The datum feature is allowed to translate rather than imposing a rotation.

The true positions of the holes remain aligned with the axis established by datum feature B and the midplane of C remains perpendicular to the co-planar axes of the three circular features. The fixture would not allow the simulator for C to rotate relative to the holes.

3DDave,
Fig 4-4 from ASME Y14.5.1-2019 (supporting ASME Y14.5-2009) is almost the same as fig 4-2 from ASME Y14.5.1M-1994.

First question:
Why fig 4-4 does not make sense?

Second question:
How would you answer my questions from the previous post?

“- There are “as produced” holes that meet translation modifier DRF |A|B|C TRM|, but do not meet |A|B|C|
- There are “as made” holes that do not meet |A|B|C TRM| DRF, but meet |A|B|C| DRF.

Which one of my assessments above would you say it is true and more importantly why? I am just trying to understand their usage correctly and their relationship”

 

[3DDave]

The previous diagram didn't show anything about the other holes and the new diagram doesn't show the perpendicularity. There is no reason to show any rotation. The DRF doesn't rotate with the part; the part is fit to the DRF.

I don't know what motivates the math group; they don't work in coordination with the main group so I don't know why they do that.

I would not answer your questions as that is for you to understand on your own. I have mentioned before - if you have a goal that you can explain in words and not symbols what it is you are trying to accomplish, then I can help with what controls and symbols can be used to achieve that goal.

I certainly don't have answers for what appear to be "I want to transform one set of conditions into another set of conditions so the differing basis for them have congruent answers" or, my least favorite, "Explain why two different things aren't the same."

 

[Burunduk]

greenimi, for this particular example (4-4) the first statement is true.
A translation modifier in the example allows the tertiary datum feature simulator to translate, so if it is able to relocate to any location it may as well move to the basic location and allow accepting an actual part with a pair of holes that would be accepted had the simulator been bound to stay at basic. On the other hand a part that can be accepted in a fixture that includes the movable datum feature C simulator, could be rejected had it been engaged with a basically fixed datum feature C simulator.

However, it is not so in all cases and I don't think it was the "design intent" of the translation modifier idea to allow additional variation. In another use of this modifier, 7-12 in Y14.5-2018, it doesn't add any leeway, or if it does it is neglectable. Instead it allows fuller and more reliable interface between the datum feature and the adjustable (RMB) datum feature simulator.

 

[pmarc]

Burunduk,
Are you sure about your assessment of greenimi's statements?

Imagine the pink center marks in greenimi's sketch representing the |A|B|C>| DRF (with green and blue lines) fall outside their respective position tolerance zones. Does this mean the holes can't fall inside their tolerance zones in the |A|B|C| DRF?

 

[Burunduk]

pmarc,
I know I shouldn't be sure when asked if I'm sure. I see what you are getting at.

But, If that part would be accepted in the A,B,C DRF, can the datum feature simulator mobility at C available under A,B,C> be used (or maybe "unused" would be more proper) to obtain the exact condition of A,B,C?
If the translating datum feature simulator must minimize any misalignment with the actual datum feature the answer should be 'no'. But I don't recall such requirement (and it may be my fault).

 

[pmarc]

As far as I can tell, one situation when the exact same condition for both DRFs could be obtained would be when the center plane of the UAME of datum slot C was exactly perpendicular to and passing through datum axis B.

The translation modifier does not cancel the default requirement for the tertiary datum feature simulator at RMB to be a set of two parallel planes at maximum separation. But unlike in case of a "regular" tertiary datum feature, the translating tertiary simulator must only be oriented to the higher order of precedence simulators.

 

[greenimi]

pmarc,

Based on your latest replay then why my assessment / question above (copied here) is not true anymore (as you clearly indicated regarding Burunduk's comment)

"“- There are “as produced” holes that meet translation modifier DRF |A|B|C TRM|, but do not meet |A|B|C|"

If it is not true in one special situation (namely here "when the center plane of the UAME of datum slot C was exactly perpendicular to and passing through datum axis B.")
that does not mean my statement is invalidated or nulified in plethora of other cases, right?

So, again, maybe my statement is not quite kosher and has limitations when your proposed scenario (call it special case) is true, but then why should I understand that in all the other cases is still not true?

Am I missing something here?
I know you can explain it to me in a very simple terms, so my ignorant / not so educated mind can understand.

As far as I can tell, one situation when the exact same condition for both DRFs could be obtained would be when the center plane of the UAME of datum slot C was exactly perpendicular to and passing through datum axis B.

The translation modifier does not cancel the default requirement for the tertiary datum feature simulator at RMB to be a set of two parallel planes at maximum separation. But unlike in case of a "regular" tertiary datum feature, the translating tertiary simulator must only be oriented to the higher order of precedence simulators.

 

[pmarc]

greenimi,
Burunduk said that only one of your statements was true. In my opinion, both are true (if we take them as general statements).