ASME Y14.41-2012 - Nominal Dimensioning Value 1

[pateli04]

I not an expert on GD&T. My background is in electrical.

I have a general question related to dimensioning a 3D model. I have an issue where measurement on the hole size falls out of the tolerance. For example, the hole is modeled at .1900 but the tolrance is .218-.229. The author cites ASME Y14.41-2012 and says it is acceptable as nominal value. He says he modeled it this way because the nominal diameter fastener for this particular type of hole (class III hole with min .218-.229) is .188. But the .188 refers to nominal fastener size. I feel like it should be modeled at .2235 or something. What do you think?

From ASME Y14.41-2012
9.2.2 Size Dimensions
A displayed feature of size dimension shall always
include a tolerance.
(a) Size Dimension and Model Agreement. Asize dimension
shall agree with the queried model value for the
same feature when the model value is rounded to the
same number of decimal places. This agreement shall
meet one of the following requirements, depending on
the tolerance expression used.

 

[CheckerHater]

I think you are right.

Unfortunately I don't have access to 2013 edition, but 2003 one clearly states that part must be modeled to exact theoretical dimensions - either minimum, maximum or mean. It doesn't mention "nominal".

So, it's either.2180, .2290, or .2235, but not .1900

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

 

[pateli04]

Thanks CheckerHater
Well here is 2003

7.2.2 Size Dimensions. A displayed feature of size
dimension shall always include a tolerance.
(a) Size Dimension and Model Agreement. A size dimension
shall agree with the queried model value for the
same feature when the model value is rounded to the
same number of decimal places. This agreement shall
meet one of the following requirements, depending on
the tolerance expression used.

Can someone verify?

 

[CheckerHater]

See also Paragraph 4.DESIGN MODEL REQUIREMENTS in 2003 (Not sure which one in 2012)

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

 

[pateli04]

Does anyone have this paragraph that checkerhater is talking about? I don't have the book, only what someone sent me.

 

[CheckerHater]

Something like this

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

 

[ctopher]

I depends on design intent.
The dim .1900 is not the nom of .218-.229.
But, if a screw size of .1900 is used, this loose hole size can be used.
If it's a thru hole, it will need to be called out on the drawing as .218-.229, not .1900.
If a threaded hole, call out the proper thd type.

Chris, CSWP
SolidWorks '16
ctophers home
SolidWorks Legion

 

[CheckerHater]

Isn't "nominal" kind of "industry" or " trade" designation, like 2 X 4 that isn't actually 2.000 X 4.000?

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

 

[JNieman]

My understanding is:
Nominal isn't a trade/industry callout. It is simply the 'named' dimension before a +/- tolerance. 'Limits' dimensions (ex: .250-.255) have no nominal.

The nominal dimension may be outside of tolerance (ex: .2500 -.0002/-.0010) which would then be modeled at .2500, though .2500 is not an acceptable number. This is the "named" (nominal) dimension.

A very common example I use to convey this is doweling parts together. Both the interference hole and the clearance hole will have the same nominal dimension, which will match the dowel size. The holes must be different, though, to achieve the proper assembly.

I am not familiar, though I'm very interested in, ASME Y14.41, so I cannot speak as to the 'appropriateness' of such dimensions and modeling. I do know it's the standard practice of at least 2 companies that were represented in the committee to develop the standard. Not that it says a lot.

So the question I have for the OP is: What's the nominal dimension? So far you've stated the limits. But is there a nominal dimension?

 

[CheckerHater]

According to ASME Y14.5-2009, Para. 1.3.56 Size, Nominal

size, nominal: the designation used for purposes of general identification.

(as opposed to "used for purposes of tolerancing"?)

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

 

[pateli04]

Well GD&T capture only shows tolerance of .2180 - .2290. When I measure the hole size its modeled at .1900. The author says that .1900 is the nominal value. Hope that answers the question.

He says an internal document (derived from ASME Y14.41-2012) gives them a preference to model the hole in "as-fabricated condition", and then to clarify "The modeled size for drilled holes refers to the standard drill size for which the hole is designed"

The above sentence is a little confusing to me...does it make sense to any of you? If so, can you rephrase for someone like me?

 

[pateli04]

Class III Hole is defined as:
Joint where close fit is obviously not required, and alignment of predrilled holes is difficult. Example; clamps, fairleads, instrument and equipment support brackets, junction boxes, lining trim, misc supports and brackets.

 

[Gilmiril]

"The modeled size for drilled holes refers to the standard drill size for which the hole is designed"

That concept would normally mean that the hole will be modeled at the nominal size of the standard drill bit, so if the drill bit is 3/16", then the modeled size would be .1875 or .188 or .19 (depending on decimal precision) regardless of actual hole tolerance. But I can't see how a 3/16" drill bit would ever achieve a dimension of .2180-.2290; that tolerance range appears more applicable to a 7/32" drill bit.

Note that a #10 UN thread has a nominal size of .190", so that could be where this nominal size originated. But that's the nominal size of the thread, and I would argue that it is NOT the nominal size of the corresponding clearance hole.

As an example (from an industry I'm more familiar with), for a 2 9/16" 5000 API Type-6B flange, the stud bolts have 1-8 UNC thread, and the bolt holes are specified as 1.12" +.06/-.02 DIA (per API Spec 6A). The nominal size of the fastener is 1" DIA, but the nominal size of the clearance hole 1 1/8" DIA. If I were to model the hole per your vendors standard, I would make it 1.12" DIA even though the resulting tolerance range is 1.10-1.18". But I would definitely NOT model it as 1.00"!

 

[weavedreamer]

ASME Y14.41-2012
9.2.2 Size Dimensions
A displayed feature of size dimension shall always include a tolerance.

(a) Size Dimension and Model Agreement. A size dimension shall agree with the queried model value for the same feature when the model value is rounded to the same number of decimal places. This agreement shall meet one of the following requirements, depending on the tolerance expression used.
​

(1) Bilateral or Unilateral Tolerance. The displayed size dimension shall equal the resolved model value.
​

(2) Limit Dimensions. The resolved model value shall equal one of the limit dimensions, or a value within the displayed range of limits.​

(3) Limit Dimensions With Plus/Plus or Minus/Minus Tolerances. The resolved model value shall not be within the displayed range of limits.​

If the queried feature had a dimension attatched stating .1900 +.0280/+.0390 this would fall under the 3rd requirement of (a) as I read it here.

As stated (.2180 - .2290), it falls under the 2nd requirement.

 

[pateli04]

Thanks everyone! You guys have been more than helpful.