Concerning tolerance for linear masurement

[Tartof]

Hi,

The question is presented in the picture below

Kindly
Paul

 

[CheckerHater]

To AK:

We use A, but we choose between A and C

 

[fsincox]

I would interpert it the way CH does. The shorter of the (2) legs of the angle itself.

CH,
I noticed you seem to have an interest in this subject before, Do you use the ISO standard alot?

Frank

 

[CheckerHater]

To Frank:

Not much, but I have big interest in everything "general", "implied", "customary" for practical reasons; also our company has European partner, so natural interest to how much info is actually hidden in their drawings

 

[Tartof]

I have two more questions which is presented in the picture below. Also the drawing is according to ISO 8015.

After i have been looking in some drawings to diffrent customers i do not see ISO 8015 anywhere. What i see is

ISO 13920
ISO 1302

Kindly

Paul

 

[fsincox]

If the part installs as I suspect, on either the surface with the balloon 6 or the directly opposing face. IMHO, both are the same as neither expresses the true functional datum reference framework and the GD&T is just window dressing (expensive window dressing as some might add).
Frank

 

[Tartof]

Fsincox, who are your answer for? because it is not for me.

 

[Tartof]

fsincox:
I just want to learn, but to learn i need a better answer then
this is "window dressing" haha. A natural follow up question to your statement would be:

What is the true function to datum reference framework in relationship to what i showed you?

 

[Belanger]

Paul ... in regards to why a third datum might be needed, think of it this way: What if the two main faces of the plate (the circled 6 and the face across from it) are not parallel to each other? Would you want the angle of the 4 holes to "follow" a particular face?

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

 

[fsincox]

Tartof,
I have proposed that the primary datum alignment would use one of the large faces, based solely on how I perceive this part will install. I hope you better understand how the part actually installs. If this is in fact a part that mounts primarily on the datum B surface then the first example is in the right direction and I am just wrong! However if one of the larger faces is how the part actually mounts you have not expressed that and so neither example really describes the functional assembly condition. Both are then just sketches to: “make a part that look something like this”.
Frank

 

[Tartof]

Thank you for the replies. I think i understand now. I have only experience from the office; I have not been in a workshop so much. When you manufacture this part you must lock it somehow, and the datum feature tells in what order that is done; an example first C Then B Then A. The larger face is a prime choice as the datum feature because of stability, then you need to take one of the sides. Then the third datum feature wouldn’t be dependent on the geometry, but you have to have it there to make the positional tolerance complete.

Who I made it in the first picture is absurd because it would mean that you would lock it by A “FIRST” then by B the outer side; which would cause problems with stability; you need to lock it by the larger side to create stability.

 

[CheckerHater]

Tartof,

About your second picture:

ISO 2768 does not apply to location of Features of Size, they are very clear about it; so you are always better off specifying "proper" location with datum framework.