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General case of angularity 2

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CheckerHater

CheckerHater

Mechanical
Sep 22, 2009
2,877
US
In recent discussion thread1103-442213 we opened Costco-sized can of worms regarding use of orientation controls.

Here is the question I wanted to ask but had a feeling that it would hijack the thread, add confusion to the discussion and not get as much attention as (in my opinion) it deserves.

I would like to collect opinions of members of the community to the problem:
How would you approach the case of angularity applied to surface randomly oriented wrt your coordinate system / DRF as shown on the picture?

Part2_yi9d4x.jpg



"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
 
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I would show two section cuts through the considered feature, section cuts' directions perpendicular to datum planes A & B for the first cut and A & C for the second cut. Each angularity control shown on a section cut view references 2 datums, both controls referencing datum plane A. Datum precedence order (edit: and basic angle specification) according to the functional interface and assembly method, and the functional purpose of that slope.
 
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I suppose a real answer would require knowledge about the function of the part, but I can say that you wouldn't need to reference a tertiary datum for the angularity. That's because the only degree of freedom a tertiary datum would lock is translation.

Sem_D220... why do you write "each angularity control"? Couldn't it be accomplished with a single FCF?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
 
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I won't comment on the "best" way because I won't pretend to know that.

I'm going to risk asking the obvious (and possibly stupid) question here - since this is a compound angle would there be an issue with taking section cuts per semiond's suggestion and specifying a basic angle to A in both views then just applying an angularity to [A|B|C] ?
 
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I wish I had seen JP's post before I posted my reply.

Modify the DRF in my reply to [A|B]. Is there an inherent issue with that?
 
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CH and everyone,
I suspect the surface is already located (profilled) to A, B and C, correct? Otherwise angularity only orients and never locates. So, you are looking for additional refinament. If I missunderstand, please let me know.
 
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@greenimi:
Let's not complicate it in that direction. We just want to check the angle :)
@all:
This is exactly what I want to see.
Sem is seeing 2 angularity controls.
JP suggests not to over-define it
chez is confident one basic angle to the [A] will do the trick.
Is there anyone else out there?

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

Lets not go overboard and say I'm "confident" !!

However a slight clarification, I was suggesting TWO basic angles to A - one defined in each of two separate section views.

Edit: a word
 
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Now that I look at it, if two basic angles were specified to [A], then perhaps an FCF with a single datum [A] could be utilized, if one does not care about constraining the one remaining additional rotational degree of freedom.
 
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OK, since there are no more suggestions so far, I will try my take.
Two angles should be enough to control orientation, so here it is:
Compound_Angularity_2_nv4lic.jpg

This follows Y14.5.1, we have feature basically related to primary and secondary datums, etc.
Now, who thinks that we can safely mess with datum order here?

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
 
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I would say yes - we can change around that datum structure to any combination you want, keeping in mind JP's note that a third datum adds nothing and that with a single datum there is a free/unconstrained DOF. (still not sure a single datum is legal with this compound angle - but nobody addressed it so I'm going to run with it until someone tells me otherwise).

I think I can envision your objection though.. That because of the way the angles are specified/defined we are limited to the DRF you are showing however my personal opinion is that although implied/resultant angles (ie: ones that might require some calculation to figure out) are still "legal" - just perhaps not recommended.
 
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This (to some extent) follows the idea of Y14.5.1 feature being oriented to the primary datum first, and further restricted by secondary (if any).
Although their approach is more "scientific" (using vectors and all).
I guess single datum is never an option though. We need 2 angles to orient vector in space. It's just we cheat the system using "projection plane" as a second datum without explicitly specifying it on the drawing.


"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
 
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CH said:
I guess single datum is never an option though. We need 2 angles to orient vector in space.
Click to expand...

I think parallelism can use a single datum reference.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
 
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CH,
Thats a good assessment, I would not have noticed that even though I think I'm taking angles to a single plane I'm relying on a projection plane normal or at an angle to another datum.

In regards to messing with datum order - do you agree or do you have the objections I predicted?

John,
So can perpendicularity both of a plane and axis, I think CH was just answering my question about compound angles - however I could well be wrong.
 
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Perpendicularity can benefit from a secondary datum reference in an open inspection. I can't think of a case where a secondary reference with parallelism would add any value.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
 
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Correct - I was focusing on the word "can".

On a related note, even if an inclined feature is not at a compound angle to the datum features - can or should it ever be referenced in an angularity callout with a single datum?
 
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chez311 -- to your last question: Sure, a single datum might be adequate if the function of the part deems that the part's rotation is not important.

Simple example: If I'm installing a kids' slide at the playground, the angularity to the ground might be important. But that's the only datum needed. I might not care if the slide faces north, south, east, or west.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
 
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I stand corrected - the most simple cases of orientation can do without second datum.

JP - that's if you install slide all by yourself. The contractor will ask where to point it - and that's another angle :)

It will take forever - to imagine all possible combinations:

Capture_jz8yeg.png


"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
 
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chez311 said:
Correct - I was focusing on the word "can".
Click to expand...

Then I wasn't clear in what I was saying.

This is what CH said:
CH said:
I guess single datum is never an option though.
Click to expand...
To which I responded:
me said:
I think parallelism can use a single datum reference.
Click to expand...

My response was to indicate that a single datum is an option.

What were you trying to say in the context of that exchange?

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
 
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John,

Sorry if that was confusing. It seemed like you were refuting what I said that perpendicularity can have only one datum, I see now that is not the case and you were just providing additional clarification that in many cases perpendicularity can benefit from a secondary datum reference where is parallelism cannot.

Actually that brings me to another question, in regards to axis parallelism could a secondary datum be employed? I agree that with a planar feature it would not benefit from a secondary datum but I would think an axis could.
 
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