Parallelism used in an assembly between two parts 5

[jeff97070]

Can someone help with the question in my subject line.

You have a assembly and you have two parts that you want be Parallel to each other how would you call that out using GT&D Parallelism.

Thank you

 

[KENAT]

Are you actually talking about machining parts after they are assembled?

Or are you saying they need to be installed in such a way that they are parallel?

I'm not sure it necessarily affects how you'd dimension it though.

Without thinking about it too much I'd probably make a functional surface of one of the parts a datum and then add FCF to the functional surface of the other part with the required parallelism called out.

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[jeff97070]

Yes two parts that are finished and then shown assemblied in a drawing using Parallelism callout between the parts.

 

[CheckerHater]

Well, you already answered your own question: you are using GD&T parallelism.
I don’t know what your level of expertise in GD&T is, so I just give a few pointers to begin with:
1. GD&T can be used on assembly drawings; there is nothing wrong with that.
2. GD&T is dealing with features, not parts. Features are material surfaces, something you can touch.
3. GD&T is based on functional requirements, so describe it in such terms as “surface “a” on the part 1 has to be parallel to surface “b” on the part 2. Surface “b” then will become what is known as “datum” and you will specify parallelism of surface “a” with relation to surface “b” to be so-and-so.
If you could describe your problem with finer detail I am sure we could give you more detailed advice as well.

 

[jeff97070]

Yes two finished parts that are than assemblied shown in a assembly drawing uisng parallelism between the parts.

 

[pmarc]

Is the actual parallelism error on the assembly level something that can be adjusted? In other words, will an operator be able to play with the two parts in order to satisfy desired parallelism tolerance?

Or maybe the actual mutual orientational relationship between the two components is a result of something that happens "in betweeen" them? In other words, is/are there another part(s) that has/have influence on the aforementioned relationship?

 

[dtmbiz]

Interesting…. parallelism applied to an assembly of parts.

Considering that features need to be inspected to DRF’s and that a DRF
consisting of theoretical datums is simulated by using gage equipment to touch actual part features; how can the gage equipment be physically located in the actual assembly?

Wouldn’t the features that are chosen for a DRF be based on part functionality and mating interfaces?
Wouldn’t those DRF features be inaccessible to gage equipment once the parts are assembled?

 

[KENAT]

not necessarily dtmbiz, we have parts in some assemblies that need to be parallel/aligned but have gaps between them that allow for inspection (the actual parallelism/alignment is usually through tooling). Plus although generally you want to be able to inspect any requirement you give, arguably that is a secondary consideration over specifying that requirement to meet functional requirements.

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[MintJulep]

Is there any way that assembly process can affect the parallelism that is achieved? By shimming, or threaded or slotted adjustment, etc?

If a dimension cannot be controlled by the assembly process then that dimension does not belong on the assembly drawing.

 

[dtmbiz]

Kenat,

Maybe not, could be the answer to my questions.
Just presented them for some thought regarding how geometric controls on an assembly drawing
are not readily interpreted according to Y14.5 (IMO).

I would agree with MintJulep that this control does not belong on an "assembly drawing"

Ref: ASME Y14.24M TYPES AND APPLICATIONS OF ENGINEERING DRAWINGS

 

[KENAT]

If the control is to be met at the assembly due to some action taken during the manufacture of the assebly then of course it belongs on the drawing.

No where in ASME that I'm aware of does it say, or even imply, that you can't use dimensions including geometric controls on an assy drawing. The important thing is that the tolerance applies at the level specified.

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[CheckerHater]

Is weldment assembly?
Where does it say it is forbidden to apply tolerances to weldment (number of standard and paragraph please)?

 

[dtmbiz]

Not only does that statement disregard the standard, it defies logic.

There is a lot that the standard "doesn't say"; however it is important to consider and apply what it "does state" and to adhere to the principles and fundmental concepts that it does establish. If in fact you want to claim compliance with it.

Y14.5 does not state that features are to be dimensioned with manufacturing requirements. It does state that process and mfg. information can be noted as such.

It does state that part features are to be defined in consideration of functionality and mating interfaces.

You can actually amend it as long as the amendments are explained.

"No where in ASME that I'm aware of does it say, or even imply, that you can't use dimensions including geometric controls on an assy drawing"

Have you actually read ASME Y14.24M ? From your statement, I believe you haven't.

If you don’t want to accept the significance, function and purpose of the various engineering drawing types... that's you're call.


done with the P.M.

 

[MintJulep]

I did not say that parallelism or any other dimension or geometric control does not belong on an assembly drawing.

I said that dimensions that cannot be affected, effected, altered or controlled by the assembly process do not belong on an assembly drawing.

Trivial example:

Flat plate A and flat plate B. Each with parallelism of its two faces controlled by some form of tolerance.

If the "assembly" is put the bottom of B on the top of A and bolt them together then the assembly process cannot control or change the resultant parallelism between the bottom of A and the top of B. You gets what you gets resultant from the actual achieved dimensions of A and B.

On the other hand, if the assembly process is "Put B on top of A and add shims at the corners until the bottom of A and the top of B are parallel within a red gnat's hair" then by all means use GD&T to identify the requirement.

 

[ewh]

I'm curious where is the standard it actual states that GD&T is only for machining (I assume) drawings and not for other assembly type drawings. It is a language that lends itsel to fabrication, as multiple tolerance stackups can make it difficult to achive a final design within reasonable cost without somehow explaining the requirements. Do we revert to adding notes stating that one surface must be parallel to another within a certain tolerance, and totally forgoe Y14.5 because we aren't dealing with a detail drawing?
Please, standard number(s) and paragraph(s) to set us straight.

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

 

[CheckerHater]

ASME Y14.5-2009 Fig.7-45 clearly shows an assembly with geometric tolerances applied.

 

[dgallup]

Lots of our assemblies have dimensions that are established by welding, crimping or otherwise altering parts or controlling their relationships. These drawings have assembly dimensions and geometric tolerances that the process must control.

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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.

 

[CheckerHater]

I participated in some government work, and nobody ever had a problem adding dimensions to the assemblies where it was needed, even checkers .
Kenat,
As you are in possession of actual Y14.24 book, would you be so kind to confirm or deny that it actually says “More than one drawing type may be combined on a single drawing”?
From my observation assembly drawing sometimes starts its life as a layout, and sometimes envelope dimensions are added to the assembly to avoid creating extra document.
It appears like, for example, layout, assembly and envelope drawings are three types that in many cases can be safely combined in single document for all the means and purposes.
So even if you follow standard “to the letter”, the letters are actually telling you how to cut the corners.

 

[lifttrucks]

ASME Y14.24-1999, 1.9:

"The characteristics of more than one drawing type may be combined into a single drawing provided the resulting combination includes the data required by the individual types. Fore example: a modification kit drawing combines a description of the modification and the kit of items needed to accomplish the modification."

 

[KENAT]

lifttrucks beat me to it. For inseperable assy & detail assy drawings it actually has example drawings with dimensions on them.

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