Dims from 3D vs ISO 2768 2

[michal77]

Hello,

I've just studied ISO standard 2768 (Tolerances for linear and angular dimensions without individual tolerance indications). I couldn't find any information about dims taken from the 3D. I wonder if this standard is also applied to dims which can be taken only from 3D or not (dims which don't exist on the drawing).
In my opinion (but I'm not totally sure) you cannot 'take' dimension from the 3D model and apply tolerance from this standard. What do you think?

thanks in advance
Michal77

 

[KENAT]

michal77, I urge you to reconsider using ISO 2768 unless you are really being forced to use it. See several threads that touch on it:

thread1103-216401
thread1103-196260
thread1103-197786

If nothing else read the very last section of I think part 1, it basically says that just because parts don't meet the tolerance in the standard doesn't mean they aren't OK so long as they are functionally acceptable or something like that. I always thought a major point of the drawing was to define what's functionally acceptable.

There is much confusion over how to apply this standard, I've had a vendor that implied you could sort of do what you say (although in my case from 2D - relationship of features with no dimension directly to each other) but I never saw this was part of the standard.

I would tend to agree that as is it can't be used directly on the model. However the principle of haveing tolerance applied based on size of feature does have some merit.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at

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

 

[benensky]

Michal77-I would believe that would be a stretch to say it does since section 1 (Scope) says, “to simplify drawing indications,” 3D models are not generally considered drawings. If your customer is sending you a 3D model or visa versa there would need to be a statement like this on the purchase or work order “Tolerances on lengths and angles on this 3D model are to be per ISO 2768-1 as if it were drawing.” That still might open a bag of worms in some cases. It does not take too long to make a drawing from a 3D model; I do not know why people do not do it. It saves a penny to execute and ends up spending a dollar in problems.
KENAT – The section I think you are referring to is A.4 in Annex A, “ . . . Exceeding the general tolerance should lead to a rejection of the workpiece only if the function is impaired.”

 

[KENAT]

benensky ,I think that's right. It's stated in the threads I link.

You also more eloquently stated one of my points, the standard is based around drawings, not models, so trying to apply it on models will take some explaining and may be more trouble than it's worth.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at

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

 

[michal77]

Many thanks for your replies. Now everything is clear for me.