Fig 4-24 of ASME Y14.5-2009

[AM Engineer]

Hello all.

My question is about Fig 4.24 of ASME 2009 version. The figure is about two coaxial diameters and single datum axis.

What is the meaning of positional tolerance control applied without any datum feature reference and how do we inspect that?

Any response shall b highly appreciated.

Best regards

 

[AM Engineer]

p

 

[Sem_D220]

Both features must fit within a single cylindrical boundary of exactly 35.1 diameter, or within 2 cylindrical boundaries of exactly 35.1 diameter perfectly aligned with each other. It controls the coaxiality of the features.

 

[greenimi]

If you remove 2X from the size dimension and replace currently shown datumless position with CF symbol, I think the drawing might have the same meaning.

 

[AM Engineer]

greenimi

So Rule 1 will be in charge when we replace 2* Position with CF?

 

[greenimi]

So Rule 1 will be in charge when we replace 2* Position with CF?

I would say Rule#1 is in charge in both cases: in the original shown case (figure from the standard) and also in my modified case (with CF symbol)

 

[chez311]

I would say they are equivalent and that rule #1 does apply in both cases. See paragraph 2.7.5 and Fig. 2-8 in Y14.5-2009 for the applicable section on how rule #1 applies to a continuous feature. It is essentially now treated as a single FOS.

 

[AM Engineer]

Thanx all for responses.
It means that boundary established by Rule 1 will be controlling co axiality of these cylindrical features to one another. Am i right??

 

[Belanger]

greenimi -- I wouldn't remove the 2X. The position can be removed and CF be added, but the 2X still connotes that it's a pair of cylinders being toleranced (via Rule #1).

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[greenimi]

I wouldn't remove the 2X. The position can be removed and CF be added, but the 2X still connotes that it's a pair of cylinders being toleranced (via Rule #1).

If that’s true then why fig 2-8 and also fig 2-9 from 2009 do not have 2x in front of their size dimension?
Just asking.

 

[AM Engineer]

Does the datumless positioning this way automatically means that two coaxial cylindrical features will be treated as one?

I m having hard time understanding this. Position is given 0 when UAME= MMC and max when UAME=LMC which means 0.2 in diamtre and 0.1 radially. In worst case if i dispalce two cylindrical features 0.1 radially by keeping both of them at LMC then outermost boundary or actual mating envelope will be greater than MMC of 35.1 which is going beyond the boundaries of Rule 1.

 

[axym]

Hi All,

Fig. 4-24 is an interesting case, because there are multiple boundaries that are coincident. Here is how I would break it down.

-There are two features (each cylinder is considered to be one feature)
-Two Rule #1 boundaries of diameter 35.1, that are fully independent of each other (from the size tolerance)
-Two virtual condition boundaries of diameter 35.1, that are perfectly coaxial to each other (from the position tolerance)

So the VC boundaries sort of duplicate the effect of the Rule #1 boundaries in this case, because the position tolerance is zero. If it was not zero, the VC boundaries would be a different size. This is what would happen in Fig. 7-59 - the Rule #1 boundaries would be 16.56 and the VC boundaries would be 16.71.

If <CF> was used in Fig. 4-24 instead of the position tolerance, here is the breakdown:

-There is one feature (the two cylinders are considered to be one feature because <CF> was applied)
-One Rule #1 boundary of diameter 35.1, from the size tolerance
-I agree with greenimi that the 2X would not be applied - this is how it is shown in Y14.5.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[axym]

AM Engineer,

If you're still getting used to positional tolerancing and MMC, then Fig. 4-24 is a bit of a tough example to be learning on.

If UAME=LMC, then the position tolerance is 0.2 (cylindrical zone 0.2 in diameter). This means that if each of the two cylinders is produced at LMC size (34.9), then the position tolerance zones are 0.2 in diameter. This would allow the cylinders to be skewed or offset within a 0.2 zone, or 0.1 radially, and stay within the 35.1 VC boundaries. If the two cylinders are produced at MMC size (35.1), the position tolerance zones are zero in diameter because the cylinders couldn't be skewed or offset at all (without violating the 35.1 VC boundaries).

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[AM Engineer]

Thanx Axym. This is how i understand now.

Applying datumless positioning like the way shown in Fig 4-24 is not the same thing as CF.

Rule 1 is not applied collectively to both features rather it is applied individually.

Am i right sir?

One thing is still unclear. How much offset the two features could be given the 0 positional tolerance at MMC?

Thanx in advance

 

[AM Engineer]

Sorry Axym. i didnt see ur second post. I read it now.

 

[Belanger]

Good point, greenimi. But I'm all about clarity. Those two ends of the part are kind of far apart (unlike Fig. 2-8 and 2-10), and they don't show extension lines running all the way across (unlike 2-10), so I leapt toward including the 2X. Shrug.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[greenimi]

Evan,

I really appreciate the level of your explanations. Makes really sense explained that way, so breaking down the callout makes it easier for end user to understand this language.

I do have one follow up question, if you don’t mind: in 2018 standard the “Two Coaxial Holes” note has been replaced by 2x in front of the composite position. See fig 10-52/2018 versus fig 7-51/2009.

In the “spirit” of your break down interpretations should I say that fig 10-52/2018 means:
- There are two features (each cylinder -Ø10 and Ø6- are considered to be two features)
- Two Rule #1 boundaries of diameter Ø10 and diameter Ø6, that are fully independent of each other (from the size tolerance)
- Two virtual condition boundaries for each line of the composite callout (two VC for PLTZF and two VC for FRTZF):

PLTZF: 9.8 and 5.8
FRTZF: 9.9 and 5.9

Two virtual condition boundaries of PLTZF are perfectly coaxial to each other. Same is applicable for the two virtual condition boundaries of FRTZF (are perfectly coaxial to each other).

Am I correct in my assessment above?

Thank you again for your input.

 

[axym]

greenimi,

Your breakdown looks correct. I suppose that we should also add that the VC boundaries for the PLTZF are perfectly oriented and located to datums A and B, as well as being perfectly coaxial to each other.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca