Y14.5-2009 Fig. 4-16, option (c) 2

[Burunduk]

I would appreciate your assessment of my rationalization of why the 7.5 MMB boundary for datum feature D in fig. 4-16 option (c) is correct. Do not hesitate to nitpick on any inaccuracies that you detect. If you think something in the reasoning is incorrect, or incomplete - tell why. And if you would explain the final conclusion in a different way, please share it. My reasoning is as follows:

1. The calculation of the maximum material boundary of a datum feature referenced in a given feature control frame takes into account the virtual condition of that datum feature as imposed by its size tolerance and any geometric tolerance that controls the datum feature in reference to the datums that precede it in the said feature control frame, with identical order of precedence. As in all cases, datum shift is not part of the above mentioned virtual condition calculation.

2. The position tolerance in fig 4-16 applied on datum feature D imposes a 7.5 mm diameter boundary basically oriented to datum A, basically located from datum axis B, and aligned with datum centerplane C. This is the full information related to the said position control.

3. Derivative from (2), there is partial (but true!) information that can be provided about the maximum material boundary of datum feature B D related to the position control applied to it: it is a 7.5 mm boundary, basically oriented to datum A and basically located from datum axis B.

4. Directly based on (1) and (3) above, the MMB boundary of datum feature B in option (c) is 7.5. Also as noted in para 4.11.6.1, "Since the perpendicularity tolerance is a refinement of the position tolerance, it is not additive".

 

[3DDave]

It seems like that, but only for some cases of tolerance. Just increase the perpendicularity tolerance on the feature used as B and then it has more clearance. The math doesn't care.

It seems like the intent is more accurate location from B.

Again, it seems like that, but that's not what the MMB of D is in the 4-16(c) example, which was the original topic.

I assume that you have not looked at or run the software to understand what it means to change the sequence from where D is toleranced to where it's used as a datum. Usually looking at the software would elicit a question as to what some particular statement does due to trying to understand.

Start a new topic when you've had a chance to understand the software; I won't follow this one as I already answered.

 

[Burunduk]

Just increase the perpendicularity tolerance on the feature used as B and then it has more clearance.

Perpendicularity error causes less clearance, not more clearance. Consider a datum feature hole produced with some specific ideally uniform actual local size and a specific MMB boundary. If it is perfectly perpendicular to the primary datum plane it has the most clearance. The more tilted it is, the less clearance is left to the boundary.

As for the MMB of D having a different shape, I don't see any benefit in defining the shape of the datum feature simulator to be identical to the boundary shape you get from the transformation from one datum reference frame to another. If the mating part of the 7 mm pin is cylindrical then the datum feature simulator should be cylindrical too. The software does what you define it to do. It doesn't know that there is a key slot on the part that adds a location constraint in a defined direction. The fact that this slot is ignored in the |A|B(M)|D(M)| DRF doesn't mean that the actual MMB boundary is not cylindrical when the final part is considered. Think of it this way: even if you ignore all datum features but A if you project the pin's "wherever it can be on the actual part" boundary to A, you get a circular outline. Not the elongated shape.

 

[3DDave]

Sorry, I had to peek. As it turns out Burunduk doesn't get that the software simulates what actually happens. If Burunduk has a different opinion then Burunduk should point out the error in that simulation or stop claiming to know what's going on.

Since the standard does not include guessing what the mating part is like, perhaps Burunduk might take this matter up with the ASME Y14.5 committee and have them include examples where other drawings of other parts and assemblies are used to define features.

More TOLERANCE leaves MORE clearance. Reading is fundamental. Changing the word TOLERANCE to ERROR is an error.

It doesn't matter if Burunduk doesn't see the benefit. Neither do anti-vaxxers, but they are also wrong.

We aren't interested in the part - we are interested in the datum simulator.

Is it a coincidence that Burunduk became a member the day after Semiond was banned? I don't think so.

 

[Burunduk]

3DDave,
Is there a positional tolerance in fig. 4-16 that allows the pin more displacement in the radial direction relative to datum feature B than in any other direction? There is none. The virtual condition created is cylindrical. I understand what you are doing - making a transformation from one DRF to another and eliminating constraints that are relevant in the original DRF and are missing in the considered DRF. You are following the rules but you are not describing physical reality. Adjusting the description of the reality to match specific math is not a better idea than using math to describe reality. You are free to think that the shape your simulator produces is not fiction and I am free to disagree.

Note taken about tolerance vs. error.
The point was that the less difference between LMC and MMB (tighter tolerances) the less clearance you get in the fixture, therefore a primary datum feature hole specified with tighter tolerances would be more likely to constrain translation.

Your last comment is not worthy of reaction.

 

[3DDave]

Sure Chipmunk.

 

[Burunduk]

Is that directed at me? I thought you decided just to peek in this thread and only talk about me in the third person. What happened?

 

[pmarc]

Not sure if anyone sees it differently, but in my opinion some the recent comments in this thread should be red flagged.

 

[greenimi]

pmarc,

Leave them alone...It is entertaining..... we need this from time to time

 

[3DDave]

You are following the rules

That's all the truth I need.

 

[CheckerHater]

3DDave,

Perfectionist like yourself should know that Chipmunk is Tamias striatus and Burunduk is Eutamias sibiricus

It's like ISO and ASME

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[3DDave]

CH?
Siberian chipmunk - Wikipedia
The Siberian chipmunk or common chipmunk (Eutamias sibiricus).

 

[Burunduk]

3DDave, I don't mind you calling me chipmunk if you aren't going to make a big deal of me calling you Cartoon Dude

 

[3DDave]

Nonetheless, an argument for an interpretation was asked for. A counter that was accepted as being to the rules was provided and then that explanation was dismissed with "The software does what you define it to do." as if I designed the software for that outcome. See those portions of axes that lie outside the axis position limit circle? Those were entirely unexpected and it took a while to realize that this simulation represented the reality of using the feature as a tertiary clocking reference.

You brought your own pre-defined notion of what the result should be, ignored the rules that produce a different result, and then accused me of faking the result.

Had you paid attention to your own question: Is there a positional tolerance in fig. 4-16 that allows the pin more displacement in the radial direction relative to datum feature B than in any other direction? you would have noticed your own prejudice in decision making by asking yourself what limit is there in the tangential direction; that is, how does D function as the clocking feature? There is a limit to its condition as the clocking feature and that is the perpendicularity. Simple geometric construction. The virtual size of a feature is not larger than the minimum envelope that contains all variations of it.

As mentioned, instead of thinking that you might be wrong and making your own drawings that show how D is to be used as a clocking feature, you accused me of lying and going to the trouble of creating a program that was so carefully created as to support that lie. Calling me a liar, even if you are doing so out of ignorance, is an irritation.

Mark Twain was credited with saying "You can't reason a man out of a position he did not reason himself into", that is, if someone has merely adopted an opinion and has done no work to support it, they will reject any alternative explanation. The other conclusion, such as it is, suggests that I am correct as I have reasoned about this rather than just jumping to an answer.

 

[Burunduk]

Disagreeing with someone isn't the same as calling him a liar.
You aren't a liar unless you realize that you are wrong and present your false conclusions as the truth.

The position tolerance applied on the pin sets a limit to the displacement (and the perpendicularity refines the orientation) of the pin in all the relevant directions relative to the datum feature simulators of the datum features referenced in that control. That limit is the virtual condition, or the MMB boundary when the pin is considered as a datum feature in a datum reference frame that includes the same higher precedence datums in the same order. Transforming the pin's virtual condition into another datum reference frame with only the radial component limited per the position tolerance and saying that the tangential and other directions are MORE restricted (per the orientation tolerance) because of the LACK of clocking reference in that direction may not be against the rules of the standard* but is in conflict with common sense.
Some may agree with your analysis, but as you witnessed, others may stick with the official version presented in the figure. Not because it is the official version, but because they are not convinced it is wrong.

*(at least if you ignore the part of para. 4.11.5 that says: "The appropriate boundary is determined by its collective effects of size, and any applicable geometric tolerances relative to any higher precedence datums.")

I don't know what makes you assume that there was no effort done by the committee before releasing this figure, but calling the work of other people "garbage" as you did in thread1103-460720 (16 Dec 19 16:40) is not supposed to earn you any more credit. Neither is mocking the forum username of someone that disagrees with you, or making various accusations.

 

[3DDave]

Saying I wrote the software to lie is calling me a liar.

And I was right. You did not reason yourself into this and I can therefore not reason you out.

If I gave you 500,000 versions of compliant parts and asked for the minimal envelope, that is, the virtual condition of the entire set, without revealing the initial tolerances you would generate exactly what the simulation gives.

To believe otherwise is not common sense.

That bit about "garbage" is called "appeal to authority" and ignores the present argument for some other unrelated item.

Focus.

 

[3DDave]

Even more coincidental, not only was a new account created the very day after the old one was terminated, it was also from Israel (either originates there or is VPNed through there) and the same habit of editing some posts 4, 5, or 6 (or more?) times to make insignificant changes while chasing arguments dependent on nit-picking the language of the standard. How else does one drive to 180 posts on tapered features, a topic done to death in previous discussions?

If it really is two different people they need to get together. Their characteristics are so similar that they would have a lot to discuss. I recommend the shopping center in Haifa with the giant Orange on the roof. Haifa is where a lot of Israeli heavy industry is and a university and likely to build items for export to the US under contract, hence the interest in ASME standards rather than ISO ones.

Still waiting for the results of the minimum bounding gauge investigation where D IS the clocking reference. That way will be convincing that I am correct. Especially with respect to the collective effects. It is already known that changing the DRF to make A primary and D secondary does not use the position tolerance, right? So it's not the original DRF/FCF that is the sole basis. The chosen references affect the collective effects which I included in the program that demonstrates the correct solution.

 

[Burunduk]

For a correct analysis of the shape and size of the MMB boundary of datum feature D in option (c), one has to understand the translation and rotation constraining aspects of the relevant datum reference frames, and the step by step establishment process of these datum reference frames.

First, the position and perpendicularity controls for the 7mm pin. The perpendicularity control references datum feature A only, and creates a 7.3 virtual condition boundary for the pin's orientation, not taking into account it's location.

For the position control, a datum reference frame is established constraining 6 degrees of freedom: datum feature A constrains 2 rotations and one translation. Suppose those are u, v, and Z. The first plane of the DRF is established, coincident with datum A. Datum feature B(M) constrains two translations: X and Y and establishes the other two planes of the datum reference frame, intersecting at right angles at datum feature B axis, which is also the Z axis. And here is an important point: these two planes are the origin references for the location of the pin. By now, there is already a cylindrical virtual condition boundary that exists, and the size of this boundary is 7.5mm, as results from the tolerance of location applied and the MMC size. But, this boundary is still not constrained in rotation around the Z axis (datum axis B): it can be anywhere 360° around it, at a fixed distance of 29mm. The tertiary datum feature C(M) doesn't take a part in setting the size of that boundary. What it does is locking its rotation about Z - the w rotation, by orienting one of the planes of the datum reference frame to be at the center of the C datum feature simulator.

So far, there is a 7.3mm boundary for orientation only and a fully constrained 7.5mm boundary for orientation and location.

Next, one has to look at the datum reference frame in option (c). The primary and secondary datum features are the same as in the position control for the pin. Datum reference A is taking care of all rotations but w, and B taking care of the X and Y translations. Which once again, makes for a meaningful location tolerance zone size, even though not all DOF are constrained. Obviously, the datum feature simulator for D, which will have to be basically oriented normal to A, has to be at the worst case size that will contain the datum feature, and take into account it's permissible orientation AND location. Therefore it is not the 7.3mm orientation-only boundary that is relevant. The relationship of datum feature D with A as primary and B(M) as secondary is per the above analysis of the position control applied to it:

The feature must be contained in a 7.5mm cylindrical boundary unconstrained in rotation about Z.

Once this is realized in the form of a datum feature simulator for D with the correct shape and size, it can work as a clocking datum reference for the 3.5mm hole controlled by the FCF in option (c).

Unfortunately, I also have to address some irrelevant to anything statements about accounts, country of origin, etc. There are tens of thousands of mechanical (and related) engineers in Israel, a large part of them dealing with GD&T daily working per either ISO or ASME. This is probably one of the most popular forums on the internet dedicated to this subject. Two out of so many posting in this forum is not an unlikely coincidence, regardless of who was banned and when, account creation dates, etc.
I looked up some posts by the said "semiond", didn't come across anything particularly negative that could suggest it's the type of guy that gets banned. Did he get banned? The profile doesn't say it, so how do you know? Also, looking at his posts history, I don't see any discussions he was involved in around the time I joined (May 2nd, 2019). It seems that the last discussion he was involved in happened way before that (June - July 2018). Did he mysteriously return on May 1st for a single post that got him banned, and then this post was deleted? I don't know what's the story there (and don't particularly care), but in case he did get banned, If I had to bet who provoked him to say whatever got him banned, I know whom I'd put my money on.

 

[pylfrm]

If I gave you 500,000 versions of compliant parts and asked for the minimal envelope, that is, the virtual condition of the entire set, without revealing the initial tolerances you would generate exactly what the simulation gives.

I think the answer would depend on what exactly you take "minimal" to mean. Your simulation shows one approach, but I can imagine others. For instance, you could find the minimal cylindrical envelope, and then further reduce the volume by discarding unnecessary portions.

Thoughts?


pylfrm

 

[Burunduk]

pylfrm, my thoughts are that there are no "unnecessary portions" to discard.
The 500,000 parts test would generate exactly the same dia. 7.5mm cylindrical virtual condition boundary. The meaning of rotation about datum axis B being unconstrained when only datum features A primary and B(M) secondary are considered is simply that the generated boundary of actual features is allowed to be located anywhere on the full 29X2=58mm pitch diameter all around datum axis B as far as the option (c) DRF is concerned.

 

[3DDave]

pylfrm,

Consider some point on theoretical datum A that lies elsewhere than the axis of theoretical datum B; then draw a line that passes through them. Then minimize the distance from each end of the axis of datum feature D of each sample to that line by rotating around the axis established by datum feature B. Their convex hull is the minimal surface. It isn't necessary to imagine fitting any particular shape. Any case where the midpoint of the axis of datum feature D is not on that line will mean that the location can be adjusted to decrease the deviation, making it smaller and since virtual condition doesn't depend on a post-manufacture adjustment, a deviation that can be decreased by moving the part is not a legitimate contributor.

If one wishes to consider the minimal enveloping diameter - the diagrams show that that diameter is larger than the 7.5 previously suggested.