ISO 13920 Parallelism reference?

[David HG]

Hello,

Please find attached picture of our drawing of a part. (High quality in attachments in the bottom of this page).

I've marked two brackets in yellow. I want to find out what parallelism tolerance is between these two mounting surfaces.
Is it correct to use the green marked dimensions as reference, and use those in ISO 13920 Table 3 as the size length? (Tolerance would then be <4,5mm).

How do I interpret usage of the nominal size l in Table 3?

 

[David HG]

Hi all,

Just to note if its not desirable to give a specific answer to the specific issue above, its completely fine to only answer:

How do I interpret usage of the nominal size l in Table 3?

 

[3DDave]

I think most avoid using this standard in favor of more explicit controls using datum references, so there is just a lack of experience.

At the least, I see no tolerance class on the drawing, so how can the correct row be chosen. Also, it looks like it's applied to centerlines/centerplanes of slots rather than surfaces. It would not apply to the reference overall dimension.

I don't have a copy of that (since I would not use it) but does it say anything about determining or applying to centerlines/centerplanes.

How To Ask Questions The Smart Way

http://www.catb.org/~esr/faqs/smart-questions.html#intro

 

[David HG]

Hi,

At the least, I see no tolerance class on the drawing, so how can the correct row be chosen.
Tolerance is ISO 13920-BF.

Also, it looks like it's applied to centerlines/centerplanes of slots rather than surfaces. It would not apply to the reference overall dimension.
The 1365±3 measure is applied to the centerplane of the slots, correct.
The (1399) measurement is on the outside edge planes of the brackets. (Since this is a reference measurement, I guess it should not be used in accordance with ISO 13920 for tolerance judgement).

I don't have a copy of that (since I would not use it) but does it say anything about determining or applying to centerlines/centerplanes.
Other than the picture in the OP, I have this page from the standard:

 

[3DDave]

OK - was expecting an explicit "CLASS ..." But I see no "B" on that chart, so they must accumulate? Don't care. Explicit datums won in this space long ago.