Help! Can't find English term for GD&T concept.

I not 100% sure, but I would say it's Tolerance Stack-up/Geometric Tolerance Analysis.

Surrogate datum features

The ASME Y14.5 standard mentions "temporary datum features" in paragraph 7.8.1, but that's more for a casting-to-machining setup.

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

Thank you all for your replies!

Cr7 :
I tought it coulb be but tolerance stack-up analyses dimensions to understand the variation of each part in an assembly: the goal is to "distribute" tolerances among parts. I am trying to basically trying to change a dimension from face A to face B to face A and C because it is more convenient. basically changing fonctionnal tolerancing to manufacturing tolerancing.

Burunduk :
I can't seem to find surrogate datum features anywhere.

Belanger :
I understand the temporary datum feature concept but this isn't what I am looking for.

Again thanks for your help.

Maybe "Manufacturing-based tolerancing" or "Tolerancing for manufacturing"?

From "Dimensioning and Tolerancing Handbook" by Paul J. Drake:

"5.9.2.3 Surrogate and Temporary Datum Features
Often, a promising candidate for datum feature has all the leadership, breadth, and character we could ever hope for and would get sworn in on the spot if only it weren’t so reclusive or inaccessible. There are plenty of other factors that can render a functional datum feature useless to us. Perhaps it’s an O-ring groove diameter or a screw thread—those are really tough to work with. In such cases, it may be wiser to select a nonfunctional surrogate datum feature, as we’ve done in Fig. 5-55. A prudent designer might choose a broad flange face and a convenient outside diameter for surrogate datum features even though in assembly they contact nothing but air."

There isn't an official word for it because the Y14.5 committee pretends it doesn't exist. Every feature selected as a datum feature is a datum feature by definition. Some are considered "functional" in that they are direct contact surfaces with mating parts the limit the location and orientation variation between them,

The word "surrogate" could have been just removed almost entirely from that description with no loss of information. The title would change to "Candidate and Temporary ..." You can tell that by the example where all the features are called "surrogate." If there is no difference there is no need for a word for that lack of difference.

Anyone anthropomorphizing surface geometry needs to take a break from writing. It's also misusing the word by making his own definition:

surrogate:
1) a person appointed to act for another; deputy.
2) (in some states) a judicial officer having jurisdiction over the probate of wills, the administration of estates, etc.

It doesn't apply to things.

There are better words than "surrogate"

substitute
replacement
representative
stand-in
standby
stopgap
alternative
expedient
makeshift

Hello Everyone,

Again thank you for all your answers. As I mentionned earlier, English is not my native language. Maybe I didn't express myself correctly, and wasn't able to convey my question correctly. I will try to better explain if you don't mind.

Let's say that I am NOT the designer of a part, I am one of the different manufacturers of the part. As such, I am not allowed to change the engineeing definition drawing. As I look at the drawing, concidering the tooling I have at hand, I find that I would be better for my process to have a the part dimensionned differently because I can machine the part without removing it from my milling machine. This dimension would only benefit my company, not the other manufacturers of the part. I understand that by doing so, the tolerance will be tighter than necessary, but I am confident in my process and I beleive I can't have a better return on investment by doing so. Obviously, the final inspection will be done per the original drawing, but I need tolerancing that can be checked while the part is still on the milling machine.

I want to basically do the change in the image below. The tolerancing here is not geometrical because the previous professor who just retired was using... well... vintage textbooks

I am trying to modernize the class before next term. Since I alway worked as a designer I tought this was heresy, but after contacting many people in the industry, they insisted that they used it a lot. Problem is they also speak French... I can't beleive French designers are using something English designers aren't...

This is simply the concept of preparing a technological process-based part drawing (with dimensions for manufacturing and in-process inspection).

Burunduk,

I feel like you're understanding what I'm looking for!
What words would describe this concept in English so I can find documentation on the subject?

3DDave said:

It's also misusing the word by making his own definition

Click to expand...

Apparently the author is not the only one using that term. See PaulJackson's comment in thread1103-325268.

supergee said:

What words would describe this concept in English so I can find documentation on the subject?

Click to expand...

Well, I would simply say technological dimensions and tolerances.

Yes - it's true - one committee member misuses a word and before long there are several making the same mistake. You would know that Walter Stites came up with it - you likely used Google to find it in the book Edited by Drake.

NO STANDARD uses that or any other term for the concept, but I'm sure you'll parrot that when they do.

What is a technological dimension? Is that in some standard or is this just more making-things-up?

Anyway, it's called creating in-process dimensions as targets for manufacturing convenience.

It's technological because it is often within the responsibility of the manufacturing technologist to assign and document these dimensions and tolerances.

Interesting approach you have - if it's not in a standard, it's "making-things-up". If it's in a standard, using the term means "parroting".
Damn, it must be hell to work with you.

Burunduk said:

Interesting approach you have - if it's not in a standard, it's "making-things-up". If it's in a standard, using the term means "parroting".
Damn, it must be hell to work with you.

Click to expand...

Optimistic vs. Pessimistic

"to work with you" vs "to work FOR you"

Just saying.....

greenimi, oh no!
Is there lower than hell??

If only "technological dimension" was used in the manufacturing industry. It's not. That's part of "making things up." It's already used elsewhere with a much different meaning, primarily in regards to societal development.

Feel free to Google: [pre]manufacturing tolerance analysis "technological dimension"[/pre]

I see a reference from Russian university papers. Maybe that's where you got the term?

Compare the Google search results for:
[pre]manufacturing tolerance analysis "in-process dimension"[/pre]

Hello!

As a Canadian hey, I don't wan't you to fight over GD&T... it not like we're dealing with life or death situations now! Oh, wait... it is.

Maybe Canadian google works differently, but I can't find anything when typing "technological dimension" nor "in-process dimension". Same thing goes for MIT library and McGill University library results.

I guess, for the sake of peace between you all, I'll use French Documents. I just don't like using ISO documentation when teaching ASME GD&T