Indication of geometric tolerances on drawings

[Angel25]

Hi everyone.

I work on design of valves for oil&gas and currently on our drawings we only indicate the general tolerances with the indication "ISO 2768-mK". We don’t indicate any specific geometric tolerances on individual dimensions/geometries.
After carrying out a functional analysis on our components, we have identified a series of specific geometric tolerances that we would like to implement on the singular parts drawings.
Before implementing geometric tolerances massively on all drawings, my team was thinking about the possibility of creating a “master document” for each type of component (e.g. body, flange, bonnet, etc.), where indicate (in a generical way) the geometric tolerances to be applied with the respective deviations, tabulated by dimensional ranges. In this case we would have the single drawings without any indications of specific geometric tolerances, which would be covered by the master document.

Personally I think that this solution, even it would lighten the drawings a lot, is not correct for a number of reasons, including:
- would it be in accordance with GD&T standars?
- the quality system should uniquely link a particular design to the master document
- the supplier who machines our components should have the master document in hand in addition to the drawing, which is impractical and could create interpretative errors since the individual drawings are not identical to those indicated on the master document.

It being understood that in my opinion the correct solution would be to indicate all the geometric tolerances directly on all the drawings, I kindly wanted to know your opinion, and if the above solution is not applicable, I would like to know where it is specified on the GD&T standards ...

Thanks for your help!

 

[TheTick]

The more links in the chain of information, the more likely something is to break.

Having a standard for tolerancing parts makes sense. Forcing the people who make the parts interpret the standard for every part is asking for trouble. Use the standard as a guide for putting explicit tolerances on the part drawings.

 

[ctopher]

I'm not familiar with "ISO 2768-mK". But, a simple note on the dwg indicating you are following this spec, and indicate standard GD&T on the dimensions are all you need. Also, training for all involved who needs to understand it.
Having a master document that spells out more than this only adds confusion and more work.

ctopher, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion

 

[drawoh]

Angel25,

The standard tells everybody what the symbols and specifications on your drawing mean. It is a complete waste of time if you do not apply the symbols and specifications.

--
JHG

 

[Angel25]

Thanks for your answers!

 

[jassco]

Hi, Angel25:

You need to think about definition of your components. You don't want to send multiple documents to potentially confuse your vendors.

If you order a part named "ABC", you should send a drawing that shows definition of this part "ABC". You should not send any other documents that are not referenced on the drawing you sent.

"the supplier who machines our components should have the master document in hand in addition to the drawing" sounds scary. Is your part defined by "its drawing" or by "the master document"? Your part needs to be defined by one document ONLY. You can have additional documents, but they will need to be referenced in your drawing.

Best regards,

Alex

 

[Angel25]

Hello jassco,

I agree with what you say. Also for us each component is uniquely defined by its drawing, so from what we have said, a single master drawing could not be applied to the drawings.

Thank you

 

[jassco]

Hi, Angel25:

You can still send the single master drawing to your vendor in addition to your component drawing as long as the component drawing calls out this single master drawing. However, you should not duplicated anything in your single master drawing that already exist in the component drawing.

If I were your vendor, I would look at your PO to determine what you order. If you would send me the single master drawing that is not referenced in your component drawing, I would not even look at it.

Best regards,

Alex

 

[Angel25]

Hi Alex,

I understand, thanks for your feedback.