Flatness callout at cross sectional view 1

[UchidaDS]

One of the drawing has a flatness callout at cross section view as shown.
My interpretation is the flatness suppose to apply to entire surface/plane. Use the CMM to measure and obtain the flatness result by probing several points along that circular plane.

One of my colleague stated that this flatness is only apply to a small sections from point 1 to point 2, not along the entire circle. As this part chucked to the lathe, this surface should be flat.

Any comments?

 

[ewh]

I would interpret that as flat all around; the points are not being referenced at the FCF and therefore meaningless, and even if there was the statement "BETWEEN 1 & 2" at the FCF, it would still be redundant because the points are coincident with the drawn extents of the surface. I think to define what your colleage thinks it means, you need to also specify that it applies only along the line of the section in the area indicated.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[Belanger]

I agree on all counts (but not the colleague's). According to paragraph 1.4 of the Y14.5 standard, the tolerance continues for wherever the feature being pointed to goes. It doesn't matter that it's shown in a section view.

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

 

[CheckerHater]

Flatness, by definition, applies to the surface, not to the line. I am having hard time imagining surface defined by just two points 1 and 2.

Your colleague needs better understanding of basic geometry.



"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[rsm7400]

As the others stated, flatness is definitely going to be the entire surface. Flatness is measured on a planar surface and not just between 2 points.

________________________________
Ryan M
Quality Engineer
3d Printer Hobbyist

 

[UchidaDS]

Definitely not two points, he mean by section (don't ask me how large is his section). He try to convince that the manufacturing method (lathe) will/should not create a lousy plane.
Following is off topic: He said it should be a parallelism callout instead of flatness-->so when this part is on CMM, then you will get a correct reading....
Is he right on this? My understanding is CMM measure the flatness or the flatness callout is regardless of how the part is oriented or shape.

 

[ewh]

While it is always a good idea to be aware of the manufacturing and inspection methods which will be used, you should tolerance the part primarily with regards to its function, not the equipment used to make or inspect it.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[CheckerHater]

Yes, Parallelism may be easier to measure if all you have is a table and dial indicator.

Yes, CMM, when programmed properly, should be able to measure flatness of inclined surface, but it depends on what kind of CMM and what kind of person operates it.

Yes, it's important to start with the function of the part. By the way, if your part serves as some sort of spacer, being "sandviched" between two other parts, it may be beneficial to specify Parallelism as well.

So, it's all up to you. Good luck!



"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[powerhound]

UchidaDS,

It's generally not a good idea to specify parts based on machine capabilities rather than function. This also applies to inspection. Your colleague's suggestion that you should specify parallelism instead of flatness because it will give you a good reading, is misguided at best. Your CMM can calculate flatness providing it's not a 30 year old CMM. It is function that should drive the specification. I agrre with CheckerHater that your colleague needs a much better understanding of GD&T and it's application.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[btrueblood]

"He try to convince that the manufacturing method (lathe) will/should not create a lousy plane. "

From experience, it's not that difficult to make a conical surface on the lathe without intending to do so. Most often, excessive tool or toolpost flex/movement is the culprit, but there are other ways.

 

[dgallup]

If he really wants to measure just the line segment between points 1 & 2 then the call out should be profile of a line. I can't imagine how that would be a useful specification but I don't know the function of the part.

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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.

 

[tbuelna]

The flatness tolerance is pretty clear. The flatness tolerance applies to the entire annular surface indicated when inspected in a free state condition. There is nothing to indicate any relationship between the flatness tolerance and the bubble callouts "1" and "2", so they do not apply.