Datum use with a pattern of a pattern?

[ligo]

See My attached jpg.

Does this Datum/Pattern say what I want it to say?


What I want it to say is:

Give me a pattern of large circles located within .02 of Datums A,B,C. And around each large circle, 4 small circles within .005 of their basic location relative to each large circle the 4 are around.

Thanks for you help.

 

[prdave00]

Thats the right idea, but you'll first need to fix your feature control frame that controls the location of datum E. Right now you have ABC but A & B are parallel so B doesn't constrain any more degrees of freedom. Maybe ACD would be appropriate. Then next to the datum E flag you'll need to say "12x individually" and again put it below the feature control frame for the 4 hole pattern. Please note that I only count 6 of the larger holes.

This method is implicitly allowed by ASME Y14.5M-1994 in section 5.7, fig 5-39 and more implicitly in Y14.5-2009. Not sure what or if your using either of these standards.

 

[prdave00]

See also

http://www.tec-ease.com/gdt-tips-view.php?q=170

By the way that second "implicit" should be "explicitly".

 

[ligo]

A, C, D datums, That is what I had intended... Must be careful of automatically use A,B,C, even though I know I set datums up differently. Thanks.

The holes are not thru, so there are 12 of the large ones, and 24 of the small ones.

Thanks for pointing me to 5.7 and fig. 5-39. Somehow I misread that section. If I understand correctly the attached jpg is how it should look.

Thanks again prdave00

 

[pmarc]

ligo,

Second print shows your intent quite well.

I have just one comment: Referencing only E datum individually in position FCF for each set of 4 holes means that each of these patterns can rotate around corresponding large hole without any limitation. If you wanted to somehow constrain this degree of freedom, you would need to add datum C or D as a datum feature after E. This is worth to consider if you want to keep patterns oriented relative to outer edges.

 

[PeterStock]

If you have holes on both sides of the part, then I am thinking that you should be refering to A for the ones on the A side and B for the ones on the B side. I am not sure of your design intent so I may be wrong.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

http://www.linkedin.com/profile/view?id=30064526&trk=tab_pro

 

[ptruitt]

Along the lines of what Peter S. was questioning, I am wondering if the opposing holes need to have a 'special relationship' with each other. That could really alter the dimensioning scheme. Especially if that included the tapped holes. Minor detail: The default tolerance for the .07 hole won't work for the thread size.

Peter Truitt

 

[ligo]

Thanks for the continued input everyone!

The pattern of large holes (really they are cutouts of different depths) could have a positional tolerance of much more than .020" and fill the actual need.

The positions of the 4 tapped holes around the large hole are locationally important, but I intended it to be ok if the 4 hole pattern is rotated around the big hole relative to C and D.

Yes It would seem to me too that referencing Datums A or B for the patterns on their respective sides is most correct. I'm not sure what I have is technically wrong the way it is. But I am sure that most any shop will understand what I want. Assuming they understand GD&T.

Each pattern of "1 large and 4 small holes" are essentially independent of all the other patterns.

I mistakenly looked at the Tol for a #1 screw when I filled in the .005, it should be more like .008 for a #2.

 

[DeanD3W]

ligo,
On the last drawing you posted the "12X INDIVIDUALLY" is correctly applied to the datum feature E symbol, but I think the other "12X INDIVIDUALLY" is in the wrong place... It should be moved to the position tolerance that applies to the four small holes around each datum feature E.

I hope this helps.

Dean Watts

http://www.d3w-engineering.com

 

[ligo]

Dean, take a look at section 5.7c and fig 5-39 in Y14.5-2009/1994

did I miss-interpret?

 

[ligo]

Dean, I think you are correct

 

[ligo]

Looking more closely at 5.7c and fig 5-39 in Y14.5-2009/1994, The case in point there is for a single feature (counterbore) in relation to another single feature (hole). In my case I have a pattern of features (4 threaded holes) in relation to a single feature (hole).

So not only was 12X INDIVIDUALLY misapplied to the large hole, rather than to the threaded holes, it should also have been applied as a 12X PATTERN OF 4, and not INDIVIDUALLY.

Attached jpg. is how I think it should look now.

 

[DeanD3W]

Hi ligo,
If you have a Y14.5-2009 take a look at figure 7-37, on page 128. The part in that figure is very similar to yours.

I think:
1) The note of the position tolerance applied to the four hole relative to E should just be "12X INDIVIDUALLY". You have a "4X" that applies to the position tolerance and to the 12X INDIVIDUALLY note as well.

2) Mentioned in prior posts is the need for a better primary datum feature... E (all 12 of them) are too shallow to reliably orient a datum reference frame so the inspector will likely keep their orientation to A... This being the case the DRF should be |A|E|, & maybe for 6 of the 12 it should be |B|E|.

3) Rotational best-fitting must be included in the evaluation of these position tolerances (with no datum feature referenced to constrain rotation about datum E)... I think it is likely better overall to go ahead and reference either C or D, so |A|E|C| or |A|E|D|. This will be simpler for a less sophisticated metrologist to evaluate. Of course this may be a step away from your functional need, so |A|E| & maybe also |B|E| would still be worth considering.

Dean

http://www.d3w-engineering.com

 

[ligo]

Thanks Dean, you bring up some good and very practical points.

Looking at it again, I agree either the 4X or the "OF 4" must go.

One of the things that has troubled me all along with regard to the 12X INDIVIDUALLY notations, is that since I have used a detail circle that is already called out as 12 PLACES, does that negate the need for the 12X INDIVIDUALLY and/or 12X PATTERN?

E is defiantly a relatively poor datum FEATURE in all cases. But using just E, does describe the design intent. Where as adding other datums adds unnecessary constraints from a "function of the part" perspective. Though it may be more troublesome for a metrologist to have only E.

 

[PeterStock]

Attached is how I would handle this part.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

http://www.linkedin.com/profile/view?id=30064526&trk=tab_pro

 

[SteveMartin]

I assume depths of the large holes are goverened by the (not shown) section views?

I obviously don't know the function of this part, but it really looks to me like you have two sets of six features (related to A|C|D and B|C|D), rather than one set of 12. Mostly because having all of the holes related to one face strikes me as odd with no orientation control between the faces. Not illegal, but odd. I would expect either A & B to have a parallelism requirement, or the holes to be oriented only to their respective side. For that matter, why datum B at all if nothing relates to it?

 

[ligo]

Peter, I think your drawing is correct and says essentially the same as mine currently. However I'm not yet convinced that applying the note INDIVIDUALLY to the 4X 2-56 holes is accurate since there are 4 holes and not just 1. The section of ASME 14.5 1994 I refer to, applies a single counter bore, to a single hole. It makes no indication of what would be correct in the case of multiple counter bores. Unfortunately I do not have a 2009 version to consult and see if has any clarification.

Steve, you are essentially correct. There is no control between A and B other than the +/-.050. That is because further refinement is not needed in this application. There is however a // relationship between the bottom each pocket and the face from which it's cut. Functionally, due to the shallowness of the pockets it will not matter if they are referenced from A or B, so long as they are // within spec, to the datum from which the // spec is applied. As such for simplicity I chose to use 12X rather than 2 6X, since it does not appear to be either wrong, or more confusing.

Thanks again to everyone for their input.

 

[PeterStock]

The INDIVIDUALLY on the 4X 2-56 holes was intended to make the pattern refer to the specific datum for that pattern. I just looked at the 2009 standard and it shows the INDIVIDUALLY on the same line as the GDT tolerance (figure 7-37 pg 128). Moving it there might be a bit clearer. Fig 8-23 of the 2009 standard shows an example where the INDIVIDUALLY is applied to a GDT tolerance with the datums being the same, just the tolerance is applied to each feature individually, not as part of the composit tolerance. What the INDIVIDUALLY refers to in a specific case should be clear in my opinion. When using it to refer to an individual datum, the INDIVIDUALLY on the datum and on the tolerance should be in the same view.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

http://www.linkedin.com/profile/view?id=30064526&trk=tab_pro

 

[PeterStock]

make that "made clear in my opinion."

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

http://www.linkedin.com/profile/view?id=30064526&trk=tab_pro

 

[ligo]

Peter, Is this what you are saying?