Virtual condition 1

[3DDave]

Suppose there is a basic brick shape - Datum feature A uses the largest face, datum feature B uses the next largest face, and datum feature C uses one of the smallest faces.

In the same face identified as datum feature A is a hole through the part of diameter E, positioned at MMB with [A|B|C] as the DRF with a tolerance of dia. X. Assume the basic dimension to B is b1, and the basic dimension to C is c1.

Now the face opposite of C is identified as datum feature D and is toleranced with a profile tolerance to [A|B|C] with a zone width of Y. Assume the basic dimension from C to D is d1.

The desire is to make a bracket sharply bent of a rectangular piece that mates to datum feature A, will have one edge coincident to datum feature B plane, and hook around the end of the part to mate with datum feature D. A bolt will pass through both parts.

What is the virtual size of that hole in the [A|B|D] DRF?

 

[Burunduk]

You mentioned datum feature D, what control uses it and what is the tolerance value for that control? If they were specified in the question the answer would be simple. Without them, the answer is subject to any personal interpretation.

The virtual condition size of a hole is defined in a given DRF when the tolerance value is modified MMC (which is what I suppose you meant by "MMB") and is calculated by the minimum size of the hole minus the specified geometric tolerance value in the same DRF. Since the hole is not controlled in the |A|B|D| DRF, the answer to your question is "not defined".

What you are probably getting at is not the virtual condition but some non-Y14.5 boundary created of the collective effects of 2 different geometric tolerances, one of which does not apply on the hole. This nameless boundary limits the variation of the surface of the hole relative to datums A and B and the unused (in a feature control frame) datum D, by different bounding sizes in different directions (because of the difference between position X tolerance in the direction normal to B and Y tolerance affecting the hole location in the direction normal to D), producing some non-cylindrical shape, once again.

 

[3DDave]

Burunduk - The answer to the first question was in the problem statement.

 

[axym]

3DDave,

There is no tolerance given for the size of the hole. Can we assume that E is the MMC size?

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[3DDave]

If you believe it matters - it would be larger or equal to the MMB diameter.

 

[axym]

3DDave,

I'm even more confused now. I'm just asking what diameter E represents, because this would affect the answer to the question.

If the specified position tolerance is X, then the MMB diameter of the hole (in the A|B|C DRF) would be smaller than the MMC diameter by X. So whether E is supposed to be the nominal diameter or the MMC diameter, E would never be equal to the MMB diameter. Unless X is zero. I'm not sure what you're getting at.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[3DDave]

What I'm saying is that you can assume either case; that's not where the insight into the situation lies.

But sure, make it easy, E is the MMC diameter.

 

[Burunduk]

With the known that E is the MMC size, the calculation for the dimensions of the boundary I mentioned earlier is E-X and E-X-Y being the "height" and "width" of the shape. This is not a virtual condition boundary.

 

[3DDave]

I'd use a different term, but the ASME Y14.5 committee never created one. So this is the one that will have to do until they create one.

"E-X and E-X-Y being the "height" and "width" of the shape" cannot be the right answer, because that doesn't fit the concepts previously given for 4-16(c), so it must be something else. Especially since the size of the SLOT was requested. I would not have mentioned the bracket if I cared about the hole in the block.

 

[Burunduk]

What is the virtual size of that hole in the [A|B|D] DRF?

(A, B, D were described as datum feature faces of the block).

... Especially since the size of the SLOT was requested. I would not have mentioned the bracket if I cared about the hole in the block.

I think that the main challenge here is understanding what the question is about.

 

[3DDave]

Let's see - it involves great detail about an additional bracket that a bolt will pass through.

Like I said before - arguing and arguing and arguing, but never dealing with the question. Twins I guess.

 

[Burunduk]

Well, you can't say I didn't try, especially judging by the "abundance" of responses you got.
By the direction those responses took, you could make a conclusion by now of what has to be clarified, but - you prefer to wrangle.

Since you don't seem to try and interpret the situation all by yourself let me help you:
The "great detail" was about the block. The datum features described belong to the block. The bracket was mentioned as the mating part. The natural way to understand it is that the intent was to clarify the function of the hole in the block.
If you mean to ask something else, ask explicitly.

 

[3DDave]

You didn't try. The virtual condition of the hole in the block can cease to exist. No realization of that because you didn't try. Before that the height decreases and the shape is not round.

The simple answer is that the virtual condition of the slot in the bracket should match the boundary of the resultant condition of the hole in the block in the mutually shared DRF.

Your replies are what happens when one just parrots what the standard says without understanding what it means in the results. I can see why you would ignore that there are two parts - recognizing them both means recognizing your previous errors which is capped with another appeal to authority argument.

If you mean to understand something, grab a pencil and a piece of paper and sketch it out.

 

[Burunduk]

The virtual condition of the hole in the block can cease to exist

Any virtual condition can cease to exist if the relevant dimensions and tolerance values allow it. One cannot tell if it is realistic for a given case with just knowing "E" "X" "Y" etc.

the virtual condition of the slot in the bracket should match the boundary of the resultant condition of the hole in the block

Again, stating the obvious.
Is that your entire point, or did you expect some formulas suggested with the parameters you provided?
To know what the virtual condition for the slot in the bracket should be one has to first describe the worst case for the hole in the block - which is what I attempted to do using the data you provided. Maybe my version of the relevant worst case boundary is incorrect, but I don't see other suggestions. Anyway, the functional description suggests that the hole in the block should be controlled for position with reference to |A|B|D| which is not what you described. If it was, it would produce what is really called a virtual condition, and in a direct manner, as it should be utilized for evaluations of this type. And yes, this is among the tools the standard provides. Tools that allow dealing with this type of cases efficiently rather than calculating cumulative effects in cumbersome ways.

 

[3DDave]

Looks back at previous responses: sees that "obvious" observations are missing.

Missing the concepts required to correctly evaluate this example is not offset by redefining the problem to a simpler, but not equivalent one. Even the attempt to fixate on the wrong problem produced the wrong answer.

It does highlight just how poorly the standard is at demonstrating the effect of datum reference choices, particularly when they include a plainly incorrect analysis of a similar case. It's infectious, leading users to make erroneous evaluations that follow a broken understanding of the rules. It's never efficient to come to the wrong conclusions; when the parts get to the factory floor and don't fit it doesn't matter how efficiently the incorrect evaluations were made.

 

[Burunduk]

Even the attempt to fixate on the wrong problem produced the wrong answer

The wrong problem - then I suppose you don't think the worst case boundary of the hole in the block should be analyzed for determining the required virtual condition for the mating slot.

I don't want to turn it into an endless quarrel, so I will just shut up and watch - perhaps someone will come up with the right answer to the right problem.

 

[Burunduk]

One last clarification before I keep my promise to shut up and allow responses by other people to generate in this thread, this is just to finish conveying my point:

To always allow a bolt pass through the bracket and the block when they are assembled together, some common inner boundary (outside the material) has to be unviolated for both the hole and the slot. Ideally, this is achieved by designating the mating surfaces as the datum features in both parts and controlling directly both features by the appropriate geometric tolerances with reference to the mutually corresponding functional datum features. This should produce virtual condition boundaries equal to or larger than the bolt's MMC, at corresponding locations.

Since a direct control of the hole in the block with reference to the functional datum features does not exist per the problem description, the inner boundary in question for the hole in the block is generated by the cumulative effects of the two geometric tolerances: position and profile specified for the hole and datum feature D respectively and calculated using the "E", "X" and "Y" data as I showed unless it will be proven that the calculation is incorrect.

Hopefully, datum features A,B,D mentioned in the question: "What is the virtual size of that hole in the [A|B|D] DRF?" (where apparently the "hole" is actually the slot in the bracket) are the faces that contact the corresponding datum features A,B,D of the block, so that at least for the slot a combined boundary generated by cumulative effects can be avoided. If it is so, this boundary is the virtual condition for the slot, and it needs to be larger than the MMC of the bolt, and basically located in at b1 from datum B and d1-c1 from datum D.

For any given subject, the basic prerequisite to being able to participate in productive discussions, and the possibility of proper application of the concepts by a large group of people (such as the users of Y14.5) is that a common language exists, meaning that the relevant terms are understood and applied in the right context. Conflating MMC and MMB, statements like: "I'd use a different term, but the ASME Y14.5 committee never created one. So this is the one that will have to do until they create one", and the mention of the resultant condition in the sentence: "The simple answer is that the virtual condition of the slot in the bracket should match the boundary of the resultant condition of the hole in the block in the mutually shared DRF." all indicate failure at realizing that principle and carelessness towards appropriate use of the tolerancing language. If I'm wrong regarding the last example and the use of "resultant condition" was per the standardized meaning, this indicates a failure to understand what type of boundary should be considered so that the parts fit when they "get to the factory floor".

 

[Burunduk]

Doesn't seem like there are going to be any more suggestions.
So, what's the correct answer to the question asked ("What is the virtual size of that hole in the [A|B|D] DRF?"), using the E Y and X parameters?

 

[greenimi]

Folks,

Since this discussion's main title is Virtual Condition may I ask, PLEASE, a question directly related with it:

Hole: Ø5.0 ±0.2
position Ø0.5 MMC |A|B|C|

If a feature of size is not subject to rule#1 (maybe has the Independency symbol or a "Perfect form at MMC not required" note applied), then
are you able to calculate the VC?
Or even the VC as a term/ name is not applicable in this case?
(maybe the VC terminology is no longer applicable when the feature does not have the rule#1 enforced)

What do you think?

Thank you very much

 

[Burunduk]

The virtual condition is not affected and still equals to 5-0.2-0.5=4.3.

Suppose that since rule #1 does not apply, the largest envelope that the actual surface of the feature does not violate is 4.75, as a result of form error (if rule #1 applied, it would need to be 4.8). It doesn't prevent us from setting a virtual condition of dia. 4.3 for the location (and orientation) of the feature.