Good Practice while stating tolerance on drawings!
Good Practice while stating tolerance on drawings!
(OP)
Hi Everyone,
We design and manufacture CNC milled parts. During the prototype stage we get them made up in China. Our manufacturer there uses DIN ISO 2768 Fine tolerances for milled metal parts. So I started to put them in our drawings under the tolerance area as - as per din iso 2768 f.
I am starting to think it is not a very good practice to ask the viewer of my drawing to find and open another document just to know tolerances. So I want to go back to the old way where it states xxdec it is +/- yy. Do you agree with me? or it doesn't really matter? Eager to hear your opinions. So either I have the entire din tolerance standard in my dwg or go back to earlier ways.
Thanks in advance!
V.
We design and manufacture CNC milled parts. During the prototype stage we get them made up in China. Our manufacturer there uses DIN ISO 2768 Fine tolerances for milled metal parts. So I started to put them in our drawings under the tolerance area as - as per din iso 2768 f.
I am starting to think it is not a very good practice to ask the viewer of my drawing to find and open another document just to know tolerances. So I want to go back to the old way where it states xxdec it is +/- yy. Do you agree with me? or it doesn't really matter? Eager to hear your opinions. So either I have the entire din tolerance standard in my dwg or go back to earlier ways.
Thanks in advance!
V.





RE: Good Practice while stating tolerance on drawings!
John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Good Practice while stating tolerance on drawings!
Asking that question on this forum = asking Allstate agent if you should have insurance
RE: Good Practice while stating tolerance on drawings!
If there's more than that to the spec, you need to provide a legit copy to your suppliers.
Personally, I'd rather the drawing stand alone, so the traveling documents in the shop don't have to include books, or worse, excerpts of books.
Mike Halloran
Pembroke Pines, FL, USA
RE: Good Practice while stating tolerance on drawings!
RE: Good Practice while stating tolerance on drawings!
From that companies will quote you a price if they want to work for you and you can choose to accept or reject it.
RE: Good Practice while stating tolerance on drawings!
Interesting!
Do you specify Rule 1 on your drawings, or do you attach copy of ASME Y14.5 to every print?
How about ASME B4? Do you attach copy every time you place H7 or g10 on the drawing?
"The viewer of your drawing" is charging you arm and leg claiming the parts will be made to specifications. Let them learn specifications!
And BTW, it's not a big deal to make small tolerance chart part of your title block.
RE: Good Practice while stating tolerance on drawings!
However, by the sounds of it you're just recording what the shop is doing anyway right?
A bigger issue is as the designer do you understand what tolerance you are invoking by referencing ISO 2768, and do you allow for them in your tolerance analysis?
Additionally have you read the entire spec and are you happy with some of what it says about not meeting it's tolerances not necessarily being cause for rejection?
The philosophy of ISO 2768 seems to be based on what a machine shop can readily achieve (or could how ever many years ago they did the study that the spec is based on), the philosophy of American drawing system (and historically the British system though as it has moved to ISO I'm not so sure any more) is more about what is required by end function.
(By the way, I believe it's been ISO 2768 for a long time, or are you deliberately referencing the old DIN?)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Good Practice while stating tolerance on drawings!
I am working to ASME Y14.5M-1994 in metric. Since we cannot use trailing zeros, the tolerance notes with the trailing zeros are not functional.
I tolerance each and every dimension, based on my requirements. I am aware of what my fabricators can do, but this is only to keep my from specifying the impossible. Tolerancing each and every dimension takes perhaps five more minutes per drawing, unless the tolerances do not work. In that, I have detected a serious design problem, and I can solve it.
--
JHG
RE: Good Practice while stating tolerance on drawings!
Over reliance on standard tolerances - be it the typical US block tolerance or something more like ISO2768 - without taking them into consideration wrt to fit & function etc. can cause all sorts of problems.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Good Practice while stating tolerance on drawings!
I've been bitten before by similar things. Tolerances change in a separate document or template, and suddenly my parts don't fit because the tolerances changed.
RE: Good Practice while stating tolerance on drawings!
I too have been surprised how this complicates things, particularly when you work to inch and the customer's part is really in metric and internal specs say I need to model all parts to the mean of the tolerance range!
Frank