Perpendicularity on multiple holes along single axis

[Raddy13]

I'm working on a machining drawing and one of the features is a hole with multiple diameters (from 15, 18, 20, and 22mm) all along the same axis. Do I have to set a perpendicularity control frame for each dimension or can I set it for the top most dimension and have it apply to entire axis for all the holes?

 

[Burunduk]

3DDave,
No, I would not argue that the number zero should never be used.
Suppose that there is tax all farmers must pay.
Would you state that since John has zero cows and zero sheep, and James has zero cows and zero sheep, they both must be farmers, because they both raise the "null cattle" and "null sheep", and therefore they must pay the tax?

 

[3DDave]

I don't see it for 7-38; the three top level FCF callouts share a single DRF. Because of that they have a simultaneous requirement because they all have the same references. The "null datum" only has an effect when no datum references are made so they have the exact same simultaneous requirement since they share a single, null, DRF.

There is a special rule for composite FCFs so that they could not be applied individually meaningfully; the notation "SIM REQT" is there, but composite on a single hole?

If one wanted to, one could have two levels of individual segments applied to each hole to duplicate the one composite tolerance, identifying the holes in each group and adding a note , but that is complicated and composite is a more compact form. This would apply to this particular example as figure 7-38 does not duplicate any of the datum features referenced for location of the holes, which in composite tolerancing, are, by rule, deprecated to providing orientation only. However, with Voelcker's notation, that location capacity could be eliminated for the more general case.

I have no explanation for the often sloppy work done in the illustrations. I wrote before, if this was the work of a single author focused on the problem, they would need a mental health check up for dementia and to fire their editor. As it is, it's just incompletely reviewed and contains some fan fiction.

The same result as INDIVIDUALLY could have achieved the same by moving the callout to a third level FCF, as in 7-45. If there is a fight between INDIVIDUALLY and SEP REQT, which look to me like synonyms, it's independent of not having datum references. The choice of which to use is decorative, not definitive.

I could place a hole dimension and size and location tolerance table on the drawing and mark an identifier next to each hole the values applied to and exactly define the members of the group and never put down #X_ and that should be acceptable.

 

[pylfrm]

I believe it to be true because it gets the "correct" results - it is consistent with the results shown in the vast majority of "means this" figures for position and profile tolerances. Further to that, the alternative explanations I looked at gave results that were not consistent.

Was "single alignment for each position or profile feature control frame segment" one of the alternative explanations you looked at? If so, what inconsistent results did it give?


pylfrm

 

[axym]

pylfrm,

I believe you're referring to my description "the effect of a pattern-creating mechanism is that it imposes the requirement that the tolerance zones for all of the applicable FCF's to be evaluated in the same alignment". I think you're right that we need to deal with multiple segments (and multiple FCF's) and my description didn't do that. I was focusing on the idea that the mechanism imposes a common alignment as opposed to just being a number-of-places indicator.

If we look at an example like Fig. 7-38 with composite FCF's (or 7-46 with multiple single-segment FCF's), the 6X, 4X and 3X pattern-creating mechanisms each apply to a segment with A|B|C and a segment with A|B. You're right that there isn't a common alignment that applies to both of the segments - there is one alignment for each segment. So your alternative explanation that applies a single alignment for each position or profile segment is definitely an improvement. We probably need to refine this description even further, as there is really more than one "level" of grouping going on. A "pattern of patterns".


Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[pylfrm]

I believe you're referring to my description "the effect of a pattern-creating mechanism is that it imposes the requirement that the tolerance zones for all of the applicable FCF's to be evaluated in the same alignment". I think you're right that we need to deal with multiple segments (and multiple FCF's) and my description didn't do that.

I wasn't actually thinking about cases involving more than one FCF segment. I guess I glossed over the "all of the applicable FCF's" portion of your statement. Do you have an example where that would apply?

I was focusing on the idea that the mechanism imposes a common alignment as opposed to just being a number-of-places indicator.

The reason for the common alignment is my main focus. Consider ASME Y14.5-2009 Fig. 8-15, and the question of why the 0.04 profile tolerance controls the relationship between datum features A and B. Your explanation is that a common alignment is required for a pattern, and datum features A and B are a pattern as defined by para. 1.3.42 due to the "2X" notation. My explanation is that a common alignment is required for everything controlled by a single FCF segment.

My explanation seems to work better for the figures that don't use one of the listed "pattern creation mechanisms" but still show a common alignment. Does it give inconsistent results in other circumstances I haven't thought of?


pylfrm

 

[axym]

pylfrm,

Some other examples where the pattern-creation mechanism applies to multiple FCF's with different alignments would be 7-47, 7-48, 7-55, and 8-23. There could/should be many other examples, but Y14.5 tends to avoid showing combinations of different FCF's on patterns. For example, it would be useful to know how perpendicularity would work as a refinement of position tolerance on a hole pattern. But this is not shown - we only see orientation tolerances applied to single features.

Do you have examples where that don't use one of the listed pattern creation mechanisms but still show a common alignment? I'm not sure that I know of any (other than 8-16 where the 2X is missing).

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[3DDave]

I get the feeling that there is an idea that just using the same references at the same condition in the same order is not enough to set up a single/simultaneous DRF, but that it can only happen if the user applies a special qualification.

Therefore, in '2009 figure 7-46, there should be 6 different gages created in order to accept the part and, because it can be very difficult to determine how much shift has happened between alignments, the distances between features in different patterns is essentially unknowable.

This does not seem like a good idea, but it sure looks like the "means this" section says it is the right answer, though it pretends there is no alignment shift between the upper and lower segment evaluation.

 

[axym]

3DDave,

In Fig. 7-46 has some interesting things going on. I'm not sure how 6 different gages would apply here though - can you clarify? I would have thought that one gage can be used for everything in A|B|C and one other gage for everything in A|B.

There is a simultaneous requirement between the three lower segments, because the FCF's are multiple single-segment and not composite. This is unfortunately not mentioned in the text. The "means this" figures are misleading at best - the lower-segment zones for the 3X and 4X patterns are shifted to the right relative to the upper-segment zones, but the zones for the 6X pattern are shifted to the left. This set of three "possible displacements" would not be allowed on the same part.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[3DDave]

I'm just going by the "means this". I agree that only two gages/alignments are required.

 

[pylfrm]

axym,

Consider a modified version of ASME Y14.5-2009 Fig. 4-2 where the hole diameter dimension is basic, the position tolerance is not present, a profile tolerance of 0.2 without datum feature references is applied to the hole on the left, and a profile tolerance of 0.3 without datum feature references is applied to the hole on the right. Would you say the two profile tolerances must be evaluated in the same alignment? If so, is that because the two holes are a pattern due to the "2X" notation on the diameter dimension?

Consider a modified version of ASME Y14.5-2009 Fig. 8-16 where the profile tolerance uses one of the vertical flat surfaces as its primary datum feature reference. Would you say the profile tolerance must be evaluated in the same alignment for both of the flat surfaces to which it applies? If so, why?

Do you have examples where that don't use one of the listed pattern creation mechanisms but still show a common alignment? I'm not sure that I know of any (other than 8-16 where the 2X is missing).

There are various examples with the All Around symbol. I suppose the relevance of these is debatable though. Perhaps it will be claimed that in these cases the profile tolerance applies to a single feature, and that a different rule requires a single alignment be used for a single feature.

One of the benefits of my explanation (common alignment for everything controlled by a single FCF segment) is that there's no need to worry about whether the toleranced portion of the part surface should be considered as one feature or multiple.


pylfrm

 

[axym]

pylfrm,

Good questions. I'm not sure that I have good answers - you're getting into the gray areas here ;^).

Regarding the modified Fig. 4-2, I don't know. My gut feeling is that the 2X should not act as a pattern-creating mechanism in this case, but I don't have anything from the standard to back that up. Does the pattern-creating mechanism need to be directly above (or below) the FCF's in order to take effect? I don't think we have enough evidence in Y14.5 to say one way or the other.

For the modified 8-16, I would say that the profile tolerance needs to be evaluated in the same alignment for both of the surfaces. The FCF with two leaders would be equivalent to two FCF's. The datum feature reference would make it a simultaneous requiremen.

I would agree that the examples in 2009 with the All Around symbol are troublesome, as the profile tolerance is described as applying to a single feature. For some reason, All Around was not included in the list of pattern-creating mechanisms. In 2018 All Around is now included in the list, but the single-feature description has not changed (see Fig. 11-24 and 11-25 in 2018).

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[Burunduk]

Regarding pylfrm's modified 4-2 example:
"2X" preceding a basic dimension does not create a pattern. Beside of the use as pattern creating mechanism nX is used to simply specify repetitive features or dimensions (per para. 1.9.5 in Y14.5-2009). Another example where 2X has nothing to do with a pattern is something like: 2X R5+/-0.3. No pattern, no interrelation between features is imposed. In order to provide a pattern, the number of places specification has to be associated with a geometrical tolerance or a with size dimension associated with a geometrical tolerance.

 

[greenimi]

Some of the grouping vs simultaneous requirements have been discussed here (Evan also has his input)

https://www.eng-tips.com/viewthread.cfm?qid=453586

 

[pylfrm]

axym,

For the modified version of Fig. 4-2, what would you do if you wanted both profile tolerances to be evaluated in the same alignment? Apply SIM REQT notes to the FCFs?

Consider a further modification of Fig. 8-16 with |profile|0.2|A| applied to the small upper flat surface, |profile|0.3|A| applied to the large upper flat surface, and a SEP REQT note applied to the double-leader |profile|0.4|A| FCF. Would you say four alignments are needed for this scheme?


pylfrm