Dimension Inspection

[UchidaDS]

Using standard ASME Y14.5M.
So I have a drawing callout for dimension inspection 2.000". This part is, let say, its round.
How should I measure this part?

--X is having the part sitting on a surface plate, then using the height gage or CMM to measure the value. Origin value is reference to the surface plate.
--Y is using either caliper or CMM to measure its thickness value,
Which is correct?

Thanks in advance!

 

[Belanger]

According to the rules of Y14.5, you must check:
-- actual local size (at various places)
-- actual mating envelope

From what I can see, neither X nor Y is doing either of those.

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

 

[UchidaDS]

Just want to clarify, the measurement will be carry out certain places and obtain the average or highest value.
It is a requested inspection dimension, no actual mating envelop is given.

 

[CheckerHater]

You said it yourself: "Using standard ASME Y14.5M."

And under ASME Y14.5 "size" dimension is an "envelope" dimension - it controls both form and size. See Para 2.7 in 2009 edition.

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

 

[UchidaDS]

Thanks for the feedback.
Refer back to the standard and comments, to my understanding, it seems "X" measurement is the correct approach, because it covers the form and size.
But according to Belanger, it is not right. What had I interpret wrong? Please help.

 

[Belanger]

We are not quite sure what you are asking. First of all, Y14.5 doesn't refer to anything called an inspection dimension. Second, we don't know what the drawing states.
But I'm assuming it's just a regular size dimension (height, for instance). In that case, the inspector needs to measure the two categories of size mentioned in my first post:

-- The "actual local size" can be measured with calipers, a micrometer, even a CMM. This should be done at various stations along the length of the part (the number of places to measure this is somewhat subjective). Each of these measurements must be within the size range allowed by the given tolerance.
-- Then the "actual mating envelope" must be measured; this is the overall size of the part throughout its full span, and thus it controls form, as CheckerHater mentioned. This can be measured with a CMM, with some sort of customized "go" gage, or another manual method. This "actual mating envelope" must be within the size range allowed by the given tolerance.

Once these two qualities are verified, we can say that the part passes the size tolerance. But in either of the things that I've described, there is (usually) no concern about wiggling the part up and down at different angles, which seems to be what your picture is asking.

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

 

[UchidaDS]

Thanks Belanger!
I am having problem of expressing.

 

[pylfrm]

UchidaDS,

I notice you never actually mentioned a tolerance. It's certainly what I would first assume when you talk about inspecting a dimension, but I suppose sometimes a tolerance is not involved. If that's the case here, then ASME Y14.5 may not be terribly relevant.

Otherwise, if a size tolerance is involved, then I think the previous answers are what you need.


- pylfrm

 

[UchidaDS]

pylfrm, the tolerance is +/-.005".
The print callout to inspect and report this dimension.

 

[UchidaDS]

Belanger : so which value should I report? The envelope or local value?

Thanks!

 

[Belanger]

According to Y14.5, the answer is both. If you are required to report a maximum and minimum, then you would report the minimum value (which for an external dimension comes from the "actual local size") and the maximum value (which for an external dimension comes from the "actual mating envelope"). See my reply of 27 January for the details on how to measure.

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