Is there a standard concentricity?

hogheavenfarm · Dec 30, 2008

I am working off a print that gives no datum or reference to the concentricity of a cylinder. My diameter on the open end is 1.520" to 1.528". What would the 'standard' tolerance for this concentric requirement? Would it be the standard dimensional tolerancing in the title block? Half the tolerance?
Any help here would be appreciated. :thanks:

Jim Wynne · Dec 30, 2008

hogheavenfarm said:
I am working off a print that gives no datum or reference to the concentricity of a cylinder. My diameter on the open end is 1.520" to 1.528". What would the 'standard' tolerance for this concentric requirement? Would it be the standard dimensional tolerancing in the title block? Half the tolerance?
Any help here would be appreciated.

Are you saying that there's a concentricity callout but no tolerance is given?

hogheavenfarm · Dec 30, 2008

Good afternoon Jim,

No, there is no allout for concentricity. It simply strikes me as there must be some standard, over which the cylinder becomes out of round, (as a 'normal' or 'standard' condition.)
The cylinder slides over a 1.500" tube, so ther is already a .010 to .014 clearance built in all the way around. (it is not a watertight or sealed assembly, more in the line of a conduit type of connection).
Our customer is concerned that there is not an even gap all the way around, but there is no requirement for this condition on the print. To what extent is excessive?
I have looked , but cannot find any accepted 'roundness' standard. When does a circle become a circle and not an oval?

Jen Kirley · Dec 30, 2008

There is no standard for when a circle becomes an oval.

If there is no callout, by default the title block's tolerance is used. This thread has another discussion of concentricity.

Who made the print? Sometimes there are errors. If your customer is concerned about clearance, in my view the subject is worth more research. It might cost less than repercussions of making parts that don't function well in use, and would probably generate more confidence on your customer's part; could help your relationship. I believe in working closely with the customer in cases like this.

trainerbob · Dec 30, 2008

I agree - Some discussion with the customer should clear up your questions. If they want you to use the tolerances from the title block it will be determined, and if they made a mistake on the drawing you will be helping out both you and them. Conversation with the customer should be a win-win situation. Goog Luck

Miner · Dec 30, 2008

hogheavenfarm said:
Good afternoon Jim,

No, there is no allout for concentricity. It simply strikes me as there must be some standard, over which the cylinder becomes out of round, (as a 'normal' or 'standard' condition.)
The cylinder slides over a 1.500" tube, so ther is already a .010 to .014 clearance built in all the way around. (it is not a watertight or sealed assembly, more in the line of a conduit type of connection).
Our customer is concerned that there is not an even gap all the way around, but there is no requirement for this condition on the print. To what extent is excessive?
I have looked , but cannot find any accepted 'roundness' standard. When does a circle become a circle and not an oval?

It sounds like you may have some confusion in terms here. Concentricity is the distance between the centers of two circular/cylindrical features. What you are describing sounds more like cylindricity or total runout.

In the absence of specific GD&T callouts, form must fall within the envelope of the feature size. Therefore, the cylindrical shape must fall 100% within the 1.520" to 1.528" tolerance. If the customer wants to control this tighter, then they must add additional control of form such as cylindricity or total runout.

Stijloor · Dec 31, 2008

Friends,

Concentricity is one of the most mis-interpreted and mis-applied geometric controls.

What is intended is usually either of two controls:

For non-rotational parts, where assembleability is a concern, use position.
For rotational parts, where form and coaxiality is a concern, use runout (total or circular).

But, without a clear reference to an applicable GD&T standard, all interpretations become a crapshoot.

Stijloor.

hogheavenfarm · Dec 31, 2008

OK, then, from what I am reading, I believe that I have the following:

This cylinder is non rotational - used for assembly, so my dimensional callout of 1.520" +.008, -.000 holds without further modification.
100% of the measurements of the inside dimension must fall within this specification, (not an average.)
The part is turned, both on the o.d. and the i.d., hence the runout question.
I wanted to have all my facts straight before conferring with the customer.
If I need to request a waiver for existing dispostion, I want to be sure of what I was requesting.

David DeLong · Dec 31, 2008

hogheavenfarm said:
I am working off a print that gives no datum or reference to the concentricity of a cylinder. My diameter on the open end is 1.520" to 1.528". What would the 'standard' tolerance for this concentric requirement? Would it be the standard dimensional tolerancing in the title block? Half the tolerance?
Any help here would be appreciated.

If the drawing does not have not show concentricity, then it doesn't apply. One would use the default tolerance for location. If the default tolerance shown in the title block is +/- .010", then the features must be on location not greater than .010.

If the title block does not refer to a specification such as ASME Y14.5M-94, then the other posts here on form also do not apply.

Cari Spears · Dec 31, 2008

hogheavenfarm said:
...my dimensional callout of 1.520" +.008, -.000 holds without further modification.
100% of the measurements of the inside dimension must fall within this specification, (not an average.)

This would be true regardless of any GD&T callouts. Nope, not an average and not fiddling around until some sweet spot is found - the entire surface of the feature must be within specification. Form tolerances are a refinement of the size tolerance; form tolerances (circularity, cylindricity, flatness and profile) fall within the size tolerance zone.

hogheavenfarm said:
...The cylinder slides over a 1.500" tube, so ther is already a .010 to .014 clearance built in all the way around. (it is not a watertight or sealed assembly, more in the line of a conduit type of connection).
Our customer is concerned that there is not an even gap all the way around, but there is no requirement for this condition on the print.

If your parts are within tolerance (if 100% of the measurements of the inside dimension fall within specification), then you've fulfilled your requirements. If there isn't enough clearance for the mating part, then your customer has a design issue.

hogheavenfarm said:
No, there is no allout for concentricity. It simply strikes me as there must be some standard, over which the cylinder becomes out of round, (as a 'normal' or 'standard' condition.)

What Miner said.

Concentricity is position/location vs cylindricity is form.

Is there a standard concentricity?

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