Seeking advice on default tolerances on Metric drawing title blocks 2

[jassco]

Hi, folks:

I'm not sure if this is a good forum to discuss the subject question. But I know we have quite many experts in this area. So, I just post my question here at GD&T forum.

At the company where I work currently, we have two sets of title blocks (or sheet formats in Solidworks). One is for Inch (Imperial) system, and the other for mm (Metric) system. On Metric (mm) title blocks, we have the following default tolerances:

TOLERANCES: .X +/- 0.50
.XX +/- 0.25
.XXX +/- 0.127
ANGLES +/- 1°

So, dimensions without tolerances can be interpreted based on the above default tolerances. We have a similar one for Inch (Imperial) title blocks that work great. But the one in mm title blocks causes controversy. This is because decimal places with mm dimensions are governed by ASME Y14.5 - 2009 (or ASME Y14.5M - 1994) (See section 1.6.1 "Millimeter Dimensioning" and section 2.3.1 "Millimeter Tolerances"). Per the standard, we are not allowed to add suffixes "0" as freely as we want to.

So, how do you guys handle default tolerances on mm drawings?

Best regards,

Alex

 

[dgallup]

We only use one default tolerance in our metric title blocks. With no trailing zeros it's not practical to have tolerances based on number of digits. I know lots of people ignore the trailing zeros rule.

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[drawoh]

jassco,

At my work, we do X=[±]0.5, X.X=[±]0.2 and X.XX=[±]0.1.

As noted by dgallup, you cannot use default decimals with ASME Y14.5. I apply [±][ ]tolerances or feature control frame to each and every feature on my metric drawings. The effort actually is trivial, unless my tolerance stack does not work. It that case, I have identified a design issue and I can now solve it.

The base dimension boxes actually are convenient. I box dimensions as I apply feature control frames. When my drawing is complete, each and every dimension either has [±][ ]tolerances, or it has a box around it. If something doesn't, my drawing is not done.

--
JHG

 

[Belanger]

...decimal places with mm dimensions are governed by ASME Y14.5 - 2009 (or ASME Y14.5M - 1994) (See section 1.6.1 "Millimeter Dimensioning" and section 2.3.1 "Millimeter Tolerances"). Per the standard, we are not allowed to add suffixes "0" as freely as we want to.

I don't think this the intent of the standard. I say you would be allowed to add extra zeros if you need to take on a certain title block tolerance which is based on the number of decimal places. Notice in paragraph 2.3.1 that everything begins with a conditional statement, such as "Where unilateral (or bilateral etc.) tolerancing is used..." So when title block tolerances are used we can ignore 2.3.1.

And while paragraph 1.6.1(c) does talk about no extra zeros, I think that is an isolated statement (about dimensions) that should be qualified by paragraph 2.1.1(e) (about tolerances).

Or do you all see 1.6.1(c) as an absolute statement? That sure would make it hard to use the notion of title block tolerances (unless they're done on a graduated scale by length, such as in ISO 2768).

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

 

[CheckerHater]

And while paragraph 1.6.1(c) does talk about no extra zeros, I think that is an isolated statement

Although there is a difference in the standard between using the word "should" and using the word "shall."

The following shall be observed where specifying millimeter dimensions on the drawing

Clearly looks like an absolute statement.

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

 

[Belanger]

That's why I was asking for other opinions. So CH, you say that the practice of using X.XX ± 0.05 etc. in a title block is absolutely prohibited (for metric drawings)?

I can agree with conclusion because of the "absolute" statements -- but it's pretty hard for me to swallow that this is what the committee intended!

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

 

[ewh]

If it is interpreted as an absolute, one solution would be to document an exception to the standards your company procedures.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[CheckerHater]

I would say yes, it violates the standard.

You can override what the standard says, providing that you document it on the face of the drawing or separate document like ewh said.

Using number of decimals can be misused and abused just like any other method, so there is no need to give it preferential treatment. Maybe it's time for it to go.

I believe we have enough other different options, but I would rather discuss global warming or healthcare than ISO 2768, even though I have strong opinions on all 3


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

 

[Belanger]

Well, by using a title block tolerance for X.XX metric dims, doesn't that in itself "document on the face of the drawing" that I'm deviating from the standard?
I'm usually one to interpret the standard quite strictly, but again, I'm really suspicious that they want to keep anyone from using the age-old title block tolerance method!

On a related note about absolute statements in the standard... See the attached graphic of a hole through a plate. A strict interpretation of the standard tells me that this hole is not a feature of size. I find that interesting, but I wonder of that's what they really intended.

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

 

[CheckerHater]

What makes you think, that it is not feature of size?

It falls perfectly well under definition of "one cylindrical or spherical surface" per Para. 1.3.32.1.

What do I miss?

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

 

[looslib]

The no trailing zeros bit us at one company when we started to enforce it. It only applies to dimensions that would have an extra zero added to meet a tolerance. 4.57 is a valid dimension to use the default title block tolerance of X.XX +- 0.08. Adding a zero to 4.6 to make it 4.60 is not allowed, it would need to be explicitly dimensioned as 4.6 +-0.08.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[CheckerHater]

And since it looks like the discussion is loosing it's original direction...

The ways to specify general tolerances without resorting to number of decimal digits:

1. Referring to ISO 2768:
UNTOLERANCED DIMENSIONS PER ISO 2768 –mK-E

2. Referring to (discontinued) ANSI B4.3-1978:
UNLESS OTHERWISE SPECIFIED, GENERAL TOLERANCES PER ANSI B4.3 MEDIUM SERIES APPLY

3. Referring to International Tolerance Grade
UNLESS OTHERWISE SPECIFIED, ALL UNTOLERANCED DIMENSIONS ARE +/- IT14/2

4. Or extended version of the same:
UNLESS OTHERWISE SPECIFIED, ALL UNTOLERANCED DIMENSIONS ARE:
HOLES H12, SHAFTS h12, OTHERS +/- IT14/2

5. Tabulating:
Recreating in part or in whole Table 1 and/or 2 from ANSI B4.3-1978

6. Using single tolerance for all dimensions:
UNLESS OTHERWISE SPECIFIED, ALL UNTOLERANCED DIMENSIONS ARE +/- 0.8

Please don’t complain about the lack of choices.


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

 

[Belanger]

What makes you think, that it is not feature of size?
It falls perfectly well under definition of "one cylindrical or spherical surface" per Para. 1.3.32.1.

Nope. The full definition says that it must be "associated with a directly toleranced dimension."

The hole was not associated with a directly toleranced direction. (If I had designated a diameter etc. then it would be a FOS.)

I'm just showing how the absoluteness of the standard sometimes makes me question whether they've followed through on all the statements. (Actually, I think I do see the bit about a FOS.)
But back to the main point -- I wonder if it's really reasonable to say that metric dimensions are prohibited from using the title block tolerance method.
Then again, if everything were perfect, these discussions would be no fun, right?

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

 

[CheckerHater]

O, boy…

No, using tile block tolerances is not prohibited by using metric dimensions.
Only the kind of tolerances based on number of decimal digits.

Now, for your incomplete view taken out of context. I could think of the following explanations that could justify it:
a. The part has several holes of the same size; one of them is dimensioned in other view.
b. The drawing represents machined part and hole is made by casting.
c. The hole is dimensioned in drawing note.
d. The hole dimension is tabulated
e. The hole dimension is queried from digital data set.
Where does it say that every hole shall be accompanied by dimension? By your logic the enclosed picture is full of holes that are not FCFc.


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

 

[jassco]

Hi, Folks:

Sorry, I was out of town and did not have a chance to participate in this wonderful discussion.

I re-read the standard before posting this response. I agree with CheckerHater that using tile block tolerances is not prohibited by using metric dimensions, only the kind of tolerances based on number of decimal digits.

The three statements that John (Belanger) brought up are all absolute statements. The standard does not prohibit us from adding whatever default tolerance we need to drawing title blocks. So, adding a default tolerance on mm drawing title blocks itself does not violate the standard. However, adding trailing zeros inconsistent with the standard clearly violates it.

I had chances of reviewing several prints from some of our major customers, and I noticed that they do follow mm dimensioning rules. And this made me wonder correctness of our current title blocks.

So, I plan to revise our title blocks. I'll try to get some feedback from my colleagues and finalize my proposal.

Thank you all for your comments!

Best regards,

Alex

 

[Belanger]

Guys -- obviously title block tolerances are not prohibited in metric. I kind of thought that it was clear we were discussing the particular method of title block tolerances that break things down by the number of decimal places.

CH -- You ask "Where does it say that every hole shall be accompanied by dimension?" The standard doesn't say that, but it does say that a hole must be "associated with a directly toleranced dimension" in order to be called a FOS. Since you were taking an absolute stance on the metric decimal places issue, I was just tossing out another item from the standard that would also seem to be absolute.
So we can address your other graphic, but my point-blank question is whether you agree that in order for something to be a FOS it must be associated with a directly toleranced dimension.

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

 

[CheckerHater]

I don't know if it's worthwhile to continue this thread, but let clarify something.

Let start with Para. 1.4 (c): "Each necessary dimension of an end product shall be shown." We often complain about lack of "shall" in the standard, but they are everywhere!

Drawing of hole without dimension does not create magical 'no size" feature. It simply violates the standard. I don't think that making bad drawings actually proves anything.
Or is Para. 1.4 (c) just another "isolated statement"?

Also, on the matter of "direct tolerancing". Y14.5 does enough to muddy the water as it is.
For example Para. 2.1.1 describes direct limits and geometric tolerances as two separate entities (clauses (a) and (b)), while Para. 2.2 states that they are both direct tolerances.

So tolerance may be direct, even if it is not attached to dimension. I would consider tolerances placed into title block or drawing note direct as well.
And even the picture you have provided may have tolerances hidden somewhere.


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

 

[Belanger]

Well, please stay with me for a little longer... An absolute interpretation of the definition of a "feature of size" must concede that a hole be "directly dimensioned" in order to be called a feature of size, right? And an absolute reading of my drawing, and also the scan you gave from the 1994 standard, would have to say that those things are not "directly" dimensioned.
(Yes, the hole that I showed would have to be dimensioned somewhere -- but the question is whether it is a dimensioned directly or indirectly.)

Hey, man, I agree with you! A hole is certainly a FOS. But my overall point is that sometimes the standard's verbiage may lead to conclusions that we all know aren't quite true or not what they intended. So I was pondering the same thing with paragraph 1.6.1(c) -- might that be a similar case where the verbiage given in the standard leads to a conclusion that wasn't intended about title block tolerances based on the number of digits? I don't know.


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

 

[CheckerHater]

I agree. Standard is not perfect, and that's why I emphasize the fact that definition of "directly dimentioned and toleranced" is far from being "direct".

According to the standard everything must (or shall?) have dimension.

According to the standard everything must be toleranced

According to the standard it is not exactly clear where "direct" ends and "indirect" starts.

That's why I see "cylinder / sphere" definition as primary and "dimentioned / toleranced" definition as secondary, redundant one.

So I see the hole on your drawing as feature of size that somebody forgot to attach dimension to, not some magical sizeless feature.

But I really don't see us getting anywhere right now... :-(

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

 

[dgallup]

Why don't you take your feature of size discussion off to another thread? It has no bearing on this discussion.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.