ISO GD&T question
ISO GD&T question
(OP)
Hi, i have a question regarding concentricity i hope some of you can help me with, i use ISO GD&T
I want 2 concentric circles to have be be toleranced concentric to eachother, to make sure they have the same center according to eachother. How shall this be illustrated? I have atteched a drawing of my idea of it, but the lead engineer disagrees. He says that using this method,there is no established centerpoint, so only one diameter can be toleranced, since the other establishes the centerpoint. But then one of the diameters doesnt have a tolerance, right?
Also shall some of the dimensions then be set as Theoretical exact dimension (TED) if i use general dimensions overall?.
I want 2 concentric circles to have be be toleranced concentric to eachother, to make sure they have the same center according to eachother. How shall this be illustrated? I have atteched a drawing of my idea of it, but the lead engineer disagrees. He says that using this method,there is no established centerpoint, so only one diameter can be toleranced, since the other establishes the centerpoint. But then one of the diameters doesnt have a tolerance, right?
Also shall some of the dimensions then be set as Theoretical exact dimension (TED) if i use general dimensions overall?.





RE: ISO GD&T question
Maybe the picture will help.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: ISO GD&T question
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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: ISO GD&T question
Also using the OD as the datum, this references the centerpoint right?
And what about TEDs?
Thank you for replies.
RE: ISO GD&T question
Certified Sr. GD&T Professional
RE: ISO GD&T question
RE: ISO GD&T question
The symbols on your last sketch look fine to me. My only comment is the circularity form control on the outside is not required to define the concentric (location) relationship. It only controls the form of the outside diameter, which technically has nothing to do with finding the datum axis from it.
Certified Sr. GD&T Professional
RE: ISO GD&T question
But for my next question, shall the OD and ID dimensions now be Theoretically exact dimensions (TED)?
RE: ISO GD&T question
Definitely NOT. They are features-of-size and must be controlled with "+/-" tolerances. TED's would only be appropriate f you applied profile to control the outside feature.
Certified Sr. GD&T Professional
RE: ISO GD&T question
RE: ISO GD&T question
Certified Sr. GD&T Professional
RE: ISO GD&T question
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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: ISO GD&T question
The ASME Y14.5 standard is depreciating concentricity. Concentricity is not really meaningful unless you have an accurate cylinder to use as a datum feature. What you have is a circle. You can define one circle as your datum feature, and use the positional tolerance to locate the other circle.
As yourself how you are going to inspect anything you define by GD&T.
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JHG
RE: ISO GD&T question
I totally agree with dgallup's and drawoh's posts. But be aware, this is a subject as deep as there are parts to design and dimension. Stay with it and the rewards will be great.
Certified Sr. GD&T Professional
RE: ISO GD&T question
May I ask why you are mixing ASME Y14.5 into this discussion. The thread title clearly states it is ISO question, and it was explained many many many times before on this forum that concentricity in ASME is totally different animal than concentricity/coaxiality in ISO.
RE: ISO GD&T question
I know there are differences, and I actually do not know what the differences are. I understand ASME Y14.5. Also, we cannot tell if the OP is visualizing a plate or a shaft. A shaft would provide a cylindrical datum feature.
Having said that, a positional tolerance should work for this?
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JHG
RE: ISO GD&T question
RE: ISO GD&T question
- ASME - coaxiality is nothing but position tolerance applied to nominally coaxial features of size. There is no extra symbol for that characteristic.- ISO - coaxiality is also nothing but position tolerance applied to nominally coaxial features of size, but it has a separate symbol (the same as concentricity symbol in ASME).
6. Concentricity tolerance:
- ASME - this geometric characteristic has very special definition (control of feature of size's median points relative to datum axis), so it is never a special case of position.- ISO - concentricity has the same symbol as coaxiality, but in addition the ACS modifier (Any Cross Section) is associated with the tolerance frame. This characteristic controls relationship between the toleranced feature and the datum feature in each cross section individually.
The strike through text is still valid, but regards to ASME and I do not want to get in trouble......with the original text posted by pmarc.
RE: ISO GD&T question
Certified Sr. GD&T Professional
RE: ISO GD&T question
If I could suggest something, I would strongly encourage you and others NOT to wait for my replies in ISO-related discussions. I do not have monopoly for knowledge (not to mention that I do not even consider myself expert in ISO GPS) and I am pretty sure many folks on this forum, including you, have a lot of meaningful and valuable things to say.
I jumped into this discussion only because I wanted to keep the discussion and OP focused on ISO stuff and not get distracted by some statements on how bad and meaningless concentricity in ASME Y14.5 is (sorry, drawoh
RE: ISO GD&T question
I really appreciate your response. My confidence with ISO improves as I follow this forum. I will be more reserved when I respond to ISO questions so I don't mislead the OP with false information. I also realize you must try to measure the knowledge of the OP from the content of the questions so you don't talk past them and add more confusion.
Certified Sr. GD&T Professional