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Concerning tolerance for linear masurement

Concerning tolerance for linear masurement

Concerning tolerance for linear masurement

(OP)
Hi,

The question is presented in the picture below

Kindly
Paul

RE: Concerning tolerance for linear masurement

Tartof,

   You have not specified a standard.  

   ASME Y14.5 specifies that any measurement between the two surfaces lies between the specified tolerances.  Any geometry that allows that, is legal.  Watch out for the angle tolerances on your drawing title block.  According to ASME Y14.5, this is what controls the perpendularity of your sides.

   I understand ISO is different.

               JHG

RE: Concerning tolerance for linear masurement

As drawoh says, any geometry.  One could take a pair of calipers, and apply the measurement at any point within the 400x400 area and if it measures within tolerance, then ok.  Again, using ASME Y14 definitions.

RE: Concerning tolerance for linear masurement

ISO 8015: Technical drawings - Fundamental tolerancing principle will give you a totally different result.  According to it the definition of a linear tolerance only controls the actual local size (2 point measurement) of a feature.  If you want to control form you need geometrical tolerances or invoke the envelope requirement.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
 

RE: Concerning tolerance for linear masurement

(OP)
Sorry, i thought this was same for all standards. I am using the ISO standard. What i am concerned about is if the measurement given in the picture with the tolerance, also includes Flatness.If it is based on cross sections then it does not include flatness.

btrueblood
My intepretation of what you said when you mentioned calipers is that you imply that it is govern by cross sections because the caliper does not cover the entire surface?

You used the word points, which is even more limiting then cross sections.

 

RE: Concerning tolerance for linear masurement

I think the ASME standard now only controls "directly opposed- features of size" not "any geometry". That is what we all thought it covered, before the 1994 version. In the simple example here it would be covered, true.
Frank

RE: Concerning tolerance for linear masurement


You can add Envelope requirement to your dimension:

20+/-0.5(E) (It's "E" in circle)

Then it will include flatness.

RE: Concerning tolerance for linear masurement

(OP)
So when manufactued the detajl could look as in the picture i have attached?

Do anyone know in what section in ISO 8015 i can read about this?

RE: Concerning tolerance for linear masurement

In ISO 8015:1985 you can read chapters 4 and 5.

However there is newest version of this document issued this year and the independency principle is described in clause 5.5.  

RE: Concerning tolerance for linear masurement


You may be out of luck if your print invokes ISO 2768-2.

Also, ISO 1101 (if specified)automatically invokes 2768.

Boy, I love where this is heading!

RE: Concerning tolerance for linear masurement

(OP)
The reason i ask this is that i want my drawings to be correct we do not need to go in to the detajls. Here in Europe most drawings refer to ISO 2768-2 in the drawing header.

So ISO 2768-2 is a subsection to ISO 8015 or how does that work?  

RE: Concerning tolerance for linear masurement

ISO 2768-2 is a separate standard. It defines general tolerances for some of geometric controls. And the flatness is amongst those controls.

It means that if you refer to 2768-2 on a drawing the flatness is limited even that nothing else beside single dimension is shown on a print like in your example. According to the standard the intent of this is practice "to simplify drawing indication"...

Another important thing which is very often overlooked is that ISO 2768 (parts 1 & 2) are dedicated for parts "that are produced by metal removal or parts that are formed from sheet metal". This means that if your part is for instance a plastic plate formed in an injection molding process, refering to ISO 2768 is not a best choice.

RE: Concerning tolerance for linear masurement

ISO and ASME are not the same!
ISO 2768-2 will specify default controls for things like flatness, if it is being invoked on the drawing properly (say"-mK", or such)?
Frank

RE: Concerning tolerance for linear masurement

(OP)
This makes me wonder, because i have seen drawings who only refer to ISO 2768-2 and not ISO 8015. Does that mean that the drawing don't have a standard?

RE: Concerning tolerance for linear masurement


Quote:

"In any event, general geometrical tolerances in accordance with this part of ISO 2768 should be used when the fundamental tolerancinf principle in accordance with ISO 8015 is used and indicated in the  drawing"

RE: Concerning tolerance for linear masurement

That is right. Whenever a drawing refers to 2768-2 it also has to refer to 8015, otherwise the standard indication is incomplete.  

RE: Concerning tolerance for linear masurement

To AK:

We use A, but we choose between A and C

RE: Concerning tolerance for linear masurement

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

RE: Concerning tolerance for linear masurement


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

 

RE: Concerning tolerance for linear masurement

(OP)
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

RE: Concerning tolerance for linear masurement

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

RE: Concerning tolerance for linear masurement

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

RE: Concerning tolerance for linear masurement

(OP)
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?

RE: Concerning tolerance for linear masurement

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

RE: Concerning tolerance for linear masurement

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
 

RE: Concerning tolerance for linear masurement

(OP)
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.

RE: Concerning tolerance for linear masurement

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.

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