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

 

[Belanger]

dg -- I take it you weren't following things. The feature-of-size bit was meant to illustrate the potential fallacy of saying that title block tolerances based on the number of decimal places are prohibited, which is indeed what this thread was about.

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

 

[pmarc]

Guys,
I am not sure what this will prove with respect to the original topic of discussion, but I would say that J-P's example wasn't too fortunate to visualize that there are situations where a feature that looks like classic feature of size does not have to be a feature of size per definition from the standard ('94 or '09). Just take a look to the attachment:

http://files.engineering.com/getfile.aspx?folder=706f9484-a9ba-4827-b660-2dfa375757a1&file=FOS.PNG

Illustration #1 shows a slot that IS a feature of size because its width is directly toleranced [directly means that the toleranced size is explicitly defined - either associated with dimension (like in this case), or defined in a general note or tabulated or specified in a document referenced on the drawing].

Illustration #2 shows a slot that IS NOT a feature of size per the Y14.5, because its width has no direct tolerance associated.

 

[KENAT]

jassco - this & similar topics have been discussed several times before on this site, maybe you can find some with the search functionality (not just the Google search the 'gray button' custom site search)

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Belanger]

Thank you pmarc. That does illustrate (better than my sketch!) why we cannot always say that something is a FOS just because it "looks" like one.
In a similar vein, I would be very interested in a solid reason why the standard would want to prohibit title block tolerances that are broken down by decimal places. Is it due to rounding? Another real reason? Or just an unintended oversight when they wrote par. 1.6.1(c)?

Sorry for pushing this idea so much. It's not merely academic, but rather something that is regularly found on automotive drawings (the auto industry is entirely metric).

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

 

[dgallup]

I think it is mainly because the rest of the world does not use decimal places to indicate default tolerances on metric drawings. I've worked for British and French companies and have seen a lot of German and Italian drawings, all metric. None of them use the number of decimal places to indicate default tolerances. Using decimal places to indicate tolerances seems to be a distinctly American concept.

And yes I did follow all the stuff above and still think the FOS part of the discussion has not bearing on the original post.

----------------------------------------

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.

 

[CheckerHater]

Good catch dgallup,

Given how close today's automotive industry is tied to British, French, German, Italian, not to mention Korean companies, I doubt that LOT of the drawings actually rely on decimal-based tolerances.

Must be automotive suppliers over-relying on "stickers" like this:

http://files.engineering.com/getfil...568e513&file=NAAMS_ASSEMBLY_section_A_006.pdf

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

 

[CheckerHater]

jassco, if you still out there, someone posted the print with default metric tolerances there:

http://files.engineering.com/getfil...-b712-44a5-b4ad-713980d9a9ae&file=Capture.PNG

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