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Spinoff2: Using orientation to control position

Spinoff2: Using orientation to control position

Spinoff2: Using orientation to control position

(OP)
The whole idea of using orientation to control location has also come up in my past work as the "GD&T guy".  A very well respected senior inspector proposed the use of parallelism to control the location of shaft keyways. His idea was that you would line up the shaft diameter (the primary datum) and then roll the keyway, itself (the secondary datum) to center and proceed to measure the resulting parallelism of the opposed sides of the keyway. His rational was that the resulting parallelism of the sides of the keyway in this representation of the installed state was important to the key not working its way out under heavy loading. I have to admit I did not feel it was technically illegal, what do you think?

RE: Spinoff2: Using orientation to control position

Ummm... picture?

RE: Spinoff2: Using orientation to control position

fsincox,

   Your example sounds like the way I model stuff in SolidWorks.  If a slot is located to a diameter, the only additional control I need on it is orientation.

   Having said that...

   The GD&T equivalent would be to call the shaft diameter as a datum, and locate (position) the slot to it.  Now, you use parallelism, perpendicularity or angle to control the orientation.  

   This is a useful approach, if orientation is more important to you than location.  If the key has clearance, a significant position error may be functional for you, while any angle error will cause stress concentration, even if you could assemble it.

               JHG

RE: Spinoff2: Using orientation to control position

(OP)
CH,
Lets try this, ASME Y14.5-2009, fig 4-32, pg 74.
In the example picture shown, you see a slot clearly drawn offset from the center of a base diameter (datum A) when the axis is drawn through the (2) holes as shown. If instead you forget the holes and find the centroid of the center of tha slot (keyway) and roll the picture horizontal to that "framework" the sides of the slot that were drawn perfectly parallel but offset will become centered but angled to that A (primary), B(secondary) alignment.
Frank

RE: Spinoff2: Using orientation to control position

(OP)
Ideally keys are fit tight (RFS) so I was told, thus making size not as important as this tendency to crawl out of the slot under loading.
Frank

RE: Spinoff2: Using orientation to control position

(OP)
I realize this is an orientation tolerance being used to control location only because of the way the framework is being established, it really is orientation as orientation, so I really could not say no.  It also involves the concept of a datum to a framework including itself sort of thing which is legal IMHO.
Frank
 

RE: Spinoff2: Using orientation to control position

Frank,
Not sure if I imagine the situation correct, but coming back to your question from the title of the thread, notice that Y14.5-2009 clearly states in 6.2: "An orientation tolerance does not control location of features".

So if your situation is that centerplane of the keyway is designed to cross the axis of the shaft exactly in the center and a parallelism callout is applied to the keyway (to its centerplane or to both surfcaces), you can actually end up with the geometry like shown on 4-32 and the part will meet the print.

RE: Spinoff2: Using orientation to control position

(OP)
You are right, basically the slot can't be off, it is just what happens to the sides when forced onto location. The orientation is not applied to the center, only the opposed sides. It did seem to be similar to what actually would be forced to happen in assembly.
Frank  

RE: Spinoff2: Using orientation to control position

fsincox,

   My interpretation of ASME Y14.5-2009 Figure 4-32 is that the holes are located from the slot.  The slot is located exclusively from the centre, datum A.  The slot defines the orientation of the part.  

   In your model, as I understand it, the hole pattern is vertical.  The slot is centred on the OD, datum A, and at an angle.

   If this were my drawing and the slot still was datum B, the slot would be horizontal, and the hole pattern would be at an angle.

    

               JHG

RE: Spinoff2: Using orientation to control position

(OP)
I am just using the picture for an example because it is a picture of a slot that is "offset" when the axes are aligned normal to the hole pattern. If there are no holes and the alignment of the axes goes throuh the centroid of the slot (roll the book about the center axis of datum A so the slot centroid point is horizontal). The sides will skew (the sides are still parallel to each other but not the newly established axes).
Frank

RE: Spinoff2: Using orientation to control position

Frank,

The way I see it, as soon as you remove round holes from Fig. 4-32  the round shaft will only be good to establish infinite number of planes, and being parallel to infinite number of planes will not locate you to anything.

I have to go home and have a drink.
 

RE: Spinoff2: Using orientation to control position

fsincox,

   Let's use Figure 4.32 as is.

   Rotation of the part is defined by the slot, designated as datum B.  We know, among other things, that the slot faces perpendicular to the drawing view, are not absolutely parallel to the outside diameter, datum A.  The allowable error is a component of the size tolerance, and the position tolerance called up on the drawing.

   I need to read up on the translation modifier.  I have not seen that before.  I don't think this affects my point, above.

   I would add a parallelism specification to this if I needed parallelism much more accurate than what the existing tolerances impose.  

    

               JHG

RE: Spinoff2: Using orientation to control position

(OP)
CH,
True, I agree there are infinate axes that are established from datum A, however, only one also goes through the centroid of the slot secondary datum B. Sorry, there is no offset dimension. the illustration was to represent the real poroduced part with the slot actually out of location, the drawing for this part would show the slot on center and no baxic dimension.
Frank

RE: Spinoff2: Using orientation to control position

(OP)
I was only using that picture as an eample of a possible actual produced part and to give a picture to look at as CH had requested. On the drawing for this part there is no position tolerance on the slot and no basic dffset dimension, therefore. the drawing for this part would imply the slot on perfect center. The diameter is still datum A and the slot is datum B. On the drawing there would be a callout on each of the sides of the slot as follows: parallel within say .001 to datum A primary, datum B secondary. RFS would be implied.
Frank

RE: Spinoff2: Using orientation to control position

As pmarc stated above, orientation tolerances do not ever locate any element of any feature.  Their tolerance zones cannot be constrained in location.  Perpendicularity, Parallelism, and Angularity tolerance zones are orientation constrainable only, they are not location constrainable.

Dean
www.d3w-engineering.com

RE: Spinoff2: Using orientation to control position

Please pardon my run-on sentence  "They are not location constrainable." should have been its own sentence.

RE: Spinoff2: Using orientation to control position

(OP)
CH,
Thank you for the new picture it is almost right and will work good as the "part as shown on the drawing" with just a few modifications.
The changes to the picture are:
1) the parallelism callout is not on the centerplane of datum B, the parallelism callouts (2) are on each of the sides of the slot.
2)the referenced datum structure for the parallelism is: A (primary), B (secondary).
Frank
  

RE: Spinoff2: Using orientation to control position

Frank,
Okay, I guess we know how your part and dimensioning scheme look like. But what is your point exactly? Are you asking whether those parallelism callouts control position of the slot? If that's so, the answer is no. You need something else to control location of the keyway, otherwise geometrical characteristic of the feature is incomplete.

RE: Spinoff2: Using orientation to control position

(OP)
If the callout is alowable, and I do not really see why it would not be, The control specified is simply orientation to a framework.
That was my only point here that some things are not as they seem and here is a case where orinetation ends up controlling location through the back door, so to speak.
Frank  

RE: Spinoff2: Using orientation to control position

Frank,

You derive datum [B] from sides of the keyhole and then you control sides of the keyhole to datum [B].
It looks too much like self-reference to me. That's why on my picture I invoke datum [A-B] which is neither [A] or [B], so it's a legal loophole of a sort.
Still, I am not sure about advantages; how is it better than specifying Location, and how would you gauge the part anyway?
 

RE: Spinoff2: Using orientation to control position

(OP)
CH,
I was not the originator of the idea, as I mentioned. I did have to calculate the alowable position tolerance implied. I believe the gentleman I worked with felt it was easy to set up and inspect, otherwise I do not think he would have proposed it. He was a senior level inspector on our company GD&T committee. I believe he also served on an ASME committee for our company relating to inspection. I was the chair and engineering representitive and had a more "is this legal" kind of role.
I do not think it is any more of a self reference than a shaft with (2) bearing diameters using A-B as a datum framework. I think you are not use to it, I really don't see it as illegal though. I was very interested at the time in pushing orientation to a frameworks not just: "the perp to A", "perp to B", stuff.
Frank

RE: Spinoff2: Using orientation to control position

CheckerHater,

   I am looking at your drawing.

   Why can the slot not just be parallel to datum A?  The cylinder defines the vertical.  That is all your parallel specification is controlling?

               JHG

RE: Spinoff2: Using orientation to control position

That was my thought also; wouldn't you have to hold the parallel tolerance twice as tight if used on both sides, or is this being accounted for in the slot width tolerance?
Hope that isn't too far in the weeds...

"Good to know you got shoes to wear when you find the floor." - Robert Hunter
 

RE: Spinoff2: Using orientation to control position

drawoh,

The way I see it, [A] by itself only defines the axis (and infinite number of planes crossing it).
To pick one plane ("vertical") you need second, "clocking" feature, hence use of [A-B].
Keyway may be off-center (like in Fig 4-32), but still parallel to axis (datum [A]), that's why I believe [A] alone is not enough.  
 

RE: Spinoff2: Using orientation to control position

(OP)
I actually wanted position, as it was simpler for me to conceptualize and calculate and more "by the book". He was a senior respected person and I was basically handed this and asked: "can we do this?". I did buy into it after a lot of thought and discussion, though, as you can see, here.
Frank

RE: Spinoff2: Using orientation to control position

Frank,
I agree with you that assigning parallelism callouts to both surfaces of the keyway relative to a centerplane derived from keyway's width does not fall under datum self-referencing, but I can't agree with your statement that in this case parallelism controls location through the back door. Look at the attached picture - I hope it explains what I mean.

http://files.engineering.com/getfile.aspx?folder=82dce5cb-c1a3-4d16-8885-ab1b90e098fc&file=parallelism_keyway.JPG

The point is, parallelism never locates - not through the back door, not through the front door, never.

RE: Spinoff2: Using orientation to control position

(OP)
pmarc,
Your picture and callouts are perfect. By calling out B as the secondary datum don't we forced it to be rolled/aligned to the center to establish the proper inspection setup?: Thus, forcing the other parts you have kindly provided to skew their keyway sides. Isn't it actually parallel in an A (primary), B (secondary) complete framework?
Frank  

RE: Spinoff2: Using orientation to control position

fsincox,

   Here is my take on it.

   Datum A provides location and a parallelism reference.  Datum B provides clocking for any subsequent features.  It is  of no relevance to this drawing.

   The positional tolerance actually controls parallelism, so the separate parallel tolerance is required only if it is more accurate.  There is no point doing this unless the diameter is accurate.  The slot probably is not a good reference unless it is more accurate than I have shown.  

   As noted by pmarc, the parallelism specification has no effect on location.   

               JHG

RE: Spinoff2: Using orientation to control position

Frank,

You can say there is implied "zero" dimension between cener of the slot and center of the shaft.
Unfortulately it is NOT "basic zero", but rather "titleblock zero", so nothing is "forced".
And how many decimal digits implied zero has, anyway?

RE: Spinoff2: Using orientation to control position

Frank,
Answering to your question: "By calling out B as the secondary datum don't we forced it to be rolled/aligned to the center to establish the proper inspection setup?", the answer is no. There would have to be a positional tolerance of keyway's width relative to datum axis A to keep the keyway centered at the shaft's axis.

As for drawoh's sketch - the idea is fine, but notice that by controlling parallelism of slot's centerplane you are not limiting mutual parallelism of its side faces. Parallelism callout says that the centerplane of actual mating envelope of the slot has to be within two parallel planes 0.05 apart, however the faces can be symmetrically divergent along the length of the shaft, so the actual mating envelope will be even perfectly parallel to datum axis A, but the only thing that will control mutual parallelism of the faces will be size tolerance of the width.

Uff... I hope I did not make the thing even worse.

RE: Spinoff2: Using orientation to control position

(OP)
I thought if something is shown on center (and no additional dimensions given)it is understood to be implied to be on center? I agree that there is no tolerance that says how close it has to be and no decimal places to zero.
Many of the drawings in the standard that position things on center rely on an impled basic zero, coplanarity also relys on a impled basic zero.
Frank

RE: Spinoff2: Using orientation to control position

Frank,
That is true. The difference is that for position callouts basic zero distance dimension applies, and for orientation callouts basic angular dimensions applies. So in case of parallelism it will be basic zero degrees, not basic zero millimeters or inches.

RE: Spinoff2: Using orientation to control position

Go pmarc Go smile

Frank - Your senior inspector friend was so far off in the weeds on this one that he ended up in the swamp.  There is absolutely no location control to be found where he was looking.  He had/has a misconception regarding orientation controls.

Dean
www.d3w-engineering.com

RE: Spinoff2: Using orientation to control position

(OP)
drawoh,
I am sorry I do not agree, so far, You admit that you know what to do with the A (primary), B (secondary) framework for other features, It is in fact the same thing I or others would do. The establishment of a shaft diameter and key for clocking is in the standard as a common framework for these type of parts. I do not see why you know how to "clock" to the key "after". I was taught that process should have no relevance to how you establish a datum framework; I believe you should establish the framework the same all of the time. That is basic to the concept of repeatable measurement. The drawing is a description of the final product not a process of making it. I feel the wording in standard supports the concept that process is irrelevant.
pmarc,
It is actually only parallelism that is being checked so I am not following the problem with the parallelism. Part of the parallelism error may be the result of what we would call location error because we may happen to notice the sides of the key are actually parallel to each other.
I will admit, I do have a stake in this because you could say I vetted it, for right or wrong. So I am not giving up that easy.
Frank
 

RE: Spinoff2: Using orientation to control position

(OP)
CH, pmarc & drawoh
I do want to thank you for your work on the illustrations. I haven't got the posting/hosting part figured out yet. This last illustration by pmarc is correct for better or worse.
 

RE: Spinoff2: Using orientation to control position

Frank,

I agree with pmarc and Dean.  A Parallelism callout isn't going to give location control, no matter how creatively it's applied.

Here's another way to look at it, that brings in some ideas on the tolerance zone mechanics of location.  A Parallelism tolerance zone is different from a Position tolerance zone in one important respect - the Parallelism zone is allowed to translate relative to the datum reference frame, and the Position zone is fixed.  This is what gives the Position characteristic (and the Profile characteristic) the extra power to control location, that the Parallelism zone does not have.

So you can establish a datum reference frame using whatever datum features you want, even the considered feature itself.  But after the DRF has been established, the Parallelism zone can still translate in any direction relative to it.  This applies whether basic dimensions are shown or not.  The zone cannot rotate relative to the DRF (this is what gives orientation control), but it can freely translate.  This translation can give the results shown in pmarc's illustration.

I believe that this agrees with the descriptions the others have given.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

Yep, nicely stated, Evan.

RE: Spinoff2: Using orientation to control position

(OP)
I think you guys do agree with each other, too.
Once an orientation zone is established by a point on a surface are not ALL other surface points to be LOCATED in a zone of width equal to the stated Tolerance? This is the concept that forces flatness control from orientation also. That provides the required control here. It is still only an orientation control, the sides are allowed to float within the greater size tolerance zone. Once a point on each side is established there are (2) zones of fixed width, parallel to the axis/framework that all of the surface point must fall (be located within). Is there not?
Frank
 

RE: Spinoff2: Using orientation to control position

(OP)
The standard ASME Y14.5M-1994, states:
 6.3.1 Form and Orientation Tolerance Zone.
"A form or orientation tolerance zone specifies a zone within which the considered feature, its line elements, its axis, or centerplane must be CONTAINED."  The word "contained" to me means located within, I am certain the main reason they did not use a term like location is exactly the problem we are having here, people would be confused and say: "orientation locates"?  You must ask yourselves what the word contained means to you, to me it forces location!
 

RE: Spinoff2: Using orientation to control position

Tolerance zone usually doesn't work alone.
It is combined with size tolerance and/or datum shift to form Virtual condition, ant it is VC that tells you where your part can and cannot be.
So, yes, the element is "contained" within tolerance zone, but zone itself is "floating around", so it does not position unless you explicitly command: "position!"
 

RE: Spinoff2: Using orientation to control position

(OP)
CH,
Once at least one point on the surface is established the tolerance zone becomes fixed/located, all other points must fall within a width (contained), and oriented to, a zone the framework established. An orientation zone can no longer float outside it's stated value or there would be no "cointainment" at all. It must contain all of the surfaces points.
Frank

RE: Spinoff2: Using orientation to control position

Quote (fsincox):


drawoh,
I am sorry I do not agree, so far, You admit that you know what to do with the A (primary), B (secondary) framework for other features, It is in fact the same thing I or others would do. The establishment of a shaft diameter and key for clocking is in the standard as a common framework for these type of parts. I do not see why you know how to "clock" to the key "after". I was taught that process should have no relevance to how you establish a datum framework;...

   You are not understanding my point.

   On my sketch, Datum B is defined, but it is not referred to.  The slot is defined entirely by Datum A.  If I were to add holes as per the diagram is ASME Y14.5, I would almost certainly need the clocking feature.  My drawing shows requirement, not fabrication procedure.  It is not a complete drawing.  All it was intended to do was illustrate a point.

   A big enough parallel error will break your positional tolerance.  The positional tolerance controls parallelism -- on my drawing to 0.2mm.  The parallel specification on my drawing, tightens the specification to 0.05mm.  There is no point in applying parallelism unless it does this.

   My final comment was that you should watch out for your datums, especially if they are features of size.  I scribbled out my sketch fairly quickly, as I was just trying to explain something.  If I were serious about this, I would not use the 0.06mm toleranced diameter to control parallelism of 0.05mm.  This is actually not relevant to the discussion.  I was just noting a problem with my sketch.   

               JHG

RE: Spinoff2: Using orientation to control position

Frank, I give up.
Not because I admit you are right, but because I have no further arguments to show that your interpretation is wrong. In my opinion there is no stronger support of my, Dean's and Evan's standpoint than paragraph 6.2 of Y14.5-2009 saying: "An orientation tolerance does not control location of features".

The sad thing is that '94 edition did not clearly state that, so now you are somehow free to interpret the statement from 6.3.1 in a way which is suitable for you. Please just tell me that basing on your understanding of 6.3.1 you do not think that form tolerances also locate.

RE: Spinoff2: Using orientation to control position

(OP)
pmarc,
I am sorry; I do hate to lose you, CH and yourself are my ISO guys. I understand arguing over and over can get tiring, as I mentioned I have a lot of thought vested into this so I do not look at it as simply a populist rule kind of issue.
 I do think I have touched on a key part of this concept before in this forum.  I made a statement in a point before that argued orientation tolerances do affect/confine location, based on the same concept of containment. It went over the same way as this is now and in the end I believe it was more an issue of semantics.
If I have a normal parallelism callout on a surface, the location (containment) of all points of the surface must fall in the band of width determined by the parallelism tolerance, that band is allowed to float inside the size tolerance, until any point on the surface is established,  once a point is found all others are contained to fall within (2) offset planes, parallel to the referenced datum and determined by that value, no?
 I think you guys may be thinking location more than what I mean, but to my way of speaking those points may no longer float just anywhere and not even anywhere within the size band but MUST be contained within the parallelism specified tolerance band width. From my point of view parallelism is forcing location at that point. I think that is all it is and is simply fundamental to the concept zone established
Frank
 

RE: Spinoff2: Using orientation to control position

(OP)
pmarc,
I did misquote the standard? Containment is not equal to forced location? If the Nazis contain people in concentration camps are they not also forcing their location?

CH,
I am working on it ;)

Frank

RE: Spinoff2: Using orientation to control position

(OP)
Dean,
My main reasons for mentioning the other gentleman were: one, to give credit where it was due, and second, to support the idea that this was not something engineering just dreamed up and "threw over the wall". I believe it was an inspection driven concept by someone who, I had every reason to believe, held a solid understanding of inspection methods and capability.
Frank
 

RE: Spinoff2: Using orientation to control position

Frank,
No disrespect or offense intended here, but wow...  You're not looking at this with an open mind and considering the comments that have very clearly stated "No" with regard to the question you're asking in your OP.

As you're reading very clear posts that tell you that orientation never controls location, including not for the case you're describing, I have this picture in my mind of you covering your ears with your hands and loudly yelling "LALALALALALA!" to yourself in order to avoid really considering what you're reading. smile

pmarc's illustration clearly showed that the slot and its two sides are absolutely not located when an orientation tolerance is applied.  How could we not be all in agreement on this??

Orientation tolerances applied to the sides of a slot will control the form and orientation of each planar surface, no more than those two things though.  Never (absolutely not ever) location in any fashion whatsoever.

Dean
www.d3w-engineering.com
 

RE: Spinoff2: Using orientation to control position

Frank,
You know, I like to play Devil's Advocate. A see idea I don't like and I am trying to make it work. It makes good mental exercise, and keeps me from getting Alzheimer's  sad
First thing I did I tried to create setup where Parallelism will somehow put keyway onto right place. (BTW, I still believe my idea was better than [A] primary [B] secondary)
I submitted my second picture not as an insult, but rather honest attempt to understand - maybe if we will start with simpler example we can find where exactly our opinions split.
So I don't think you are losing anyone here.
Just keep on trying! Well-behaved people rarely accomplish anything.  smile
 

RE: Spinoff2: Using orientation to control position

(OP)
CH & Others,
I am sorry that was a bad analogy, I was trying to use the concept in a different sense to accentuate the effect I feel occurs.  I did start this thread so do I feel I have the right to pursue my line of thinking as far as I need to get this into my head. Unless I can get someone else to understand I am not sure that actual communication has occurred. To say: "the standard does not say this so I believe it", sounds to me more like: "I don't like to think about this just believe it", that I cannot do!  I am also not an: "Everyone else thinks this way so I should too", kind of guy. I, like CH, will tend to be a "well why not?" kind of guy. Others are free to drop in or drop out as they feel, I will be sad to lose their input but, we will meet again.
 
If it makes you feel better to not use the term location for this effect, I am fine with that, the standard states "contained". It is the actual effect that occurs that is the important key not the words we use.

Look at basic parallelism ASME Y14.5M-1994, Fig. 6-30. We all know the surface can float inside a larger size zone, but, once even one single point is established the zone becomes contained to .12(mm) wide, the parallelism zone value.  Is that not the effect you see? (I know, possibly less if at the MMC boundary, of course)
Frank
 

RE: Spinoff2: Using orientation to control position

Frank,

I admire your willingness to think in new directions and entertain a controversial idea.  Sometimes this leads to a useful new conceptual approach to something previously thought to be well understood, sometimes it leads to a blind alley.  As Dean and the other members of this forum can attest, I've had a few controversial ideas myself which have turned out both ways.  Once in a while I might see things that nobody else has, sometimes I'm just seeing things.

I think I understand the point you're trying to make with location of points within a zone, having pondered things like this on long airplane flights home from GD&T camp.  One could argue that confining all of the points on a feature to a tolerance zone locates them relative to each other.  Or that the points on the feature must all be located to some reference plane, but we can arbitrarily pick the reference plane.  This concept has practical application in metrology and measurement data reporting, where we sometimes report the locations of surface points relative to an arbitrary reference plane to illustrate Flatness or Parallelism deviations.

But the Y14.5 standard uses a more narrow definition of "location", effectively confining it to the location of entire features (or entities extracted from a feature) relative to other features or relative to datums.  Inter-feature location and not intra-feature location, if you will.  So the extension of the word "containment" to mean "location" is unfortunately a blind alley, at least as far as application to the current Y14.5 standard is concerned.   

So keep the questions and ideas coming.  Your posts have made me think of things that I wouldn't have thought of otherwise.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

(OP)
CH,
Well legally or otherwise?
Can I get the part made with a good possibility of working for you?  Yes
Is the part actually functionally defined?  Probably not
 I work with drawings like yours all of the time. GD&T is not a popular subject with most of the people I know and work with, this is why I bother you guys. I believe the 1973 standard and earlier attempted to define "legally" what a drawing like this means.  Under the newer versions of the standard they have stepped away from +/- style definition to the point where it is harder to be sure that they mean "legally". Meanwhile, out in the real world we work with these drawings all of the time. This has been one of my many points of dissatisfaction with the situation we find ourselves in. The standard committees spend time creating new way of doing these thing which most, I see, in the industry try to avoid and then they proceed to cut out the legs from underneath those of use that have this existing work in the field.
Just a suggestion (I do not want to lose you),  If this is not directly relevant to a point here, let's start another thread for it.
Frank
 

RE: Spinoff2: Using orientation to control position

Frank,

I completely agree that the actual effect is more important than the words.  Sometimes the words get in the way, as we often find in our debates on this forum.  Sometimes we have to look away from the words, and look to the geometry.  When pmarc took the time to make a simple diagram of the off-center keyway, he probably saved us all a lot of time trying to describe the same thing in words.

You're saying that the entire surface must located within a certain zone in order to conform to the Parallelism requirement, once the first point has established.  Technically this might be true, but again it doesn't match Y14.5's definition of location.  It's not controlling the location of the feature relative to other features or relative to a datum (a datum in Y14.5 is established from a labeled datum feature).  You're using the first established surface point as a de facto datum for location of the others, which imposes a constraint that is not part of Parallelism.  There is no requirement for the Parallelism zone to be located to anything, including the considered feature itself - it can freely translate.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

Frank,
I already said in one of my posts, that one can make a living by producing good parts from bad prints.
But the purpose of this forum is to make 'good' prints, right?
 

RE: Spinoff2: Using orientation to control position

(OP)
Evan, CH, Dean, drawoh  & any others that may have followed along,
I am a supporter of standards so I can accept that the terminology is defined by them and we need to be careful when using terms.  The problem is I still need a way to refer to things in our somewhat social context.
 I had always referred to a zone of form (yes, I miss you already pmarc, wherever you are,) and orientation as: "all of the features points must be located within a zone of blah, blah...". If I should not say that, I can accept that you would prefer that I use different terminology in the interest of common understanding.  I might now use the word contain, because I had just looked it up, yesterday.
In the end I still need a way to refer to the effect the orientation tolerance has on the surfaces. I believe it is forced to be contained within a .XXX zone that is, as stated. It is established by the datum framework which contains the centroid of the feature itself, therefore, it is by definition on center.  In my opinion, establishing a framework like this is very similar, conceptually, to the A-B framework. Some here do not like or understand A-B either, but, it has been in the standard since: probably MIL-STD-8? This in my mind means they lost that argument long ago, (It is particularly OK if you use it for runout, one of my other pet-peeves).
Frank
 

RE: Spinoff2: Using orientation to control position

(OP)
I looked up the 2009 statement pmarc referenced, which is not in the 1994 standard and I agree, it clearly says orientation does not control location. I can't find their definitition of location can some one reference the page for me, 2009 is fine? I am working and I am doing the best I can to keep up.
Frank
 

RE: Spinoff2: Using orientation to control position

(OP)
CH,
I agree with your statement.
The important difference I see in the (2) hole block sketch and my example is you were not using datums other than a single perpendicular plane to establish measurement, thus we are not tied to the concept of perfection, that is establised by using a datum framework.
Frank

RE: Spinoff2: Using orientation to control position

(OP)
Sorry, It was 1966 standard.
There is no runout in MIL-STA-8 it is only my dear old friend concentricity defined like rounout another error the standard made that curses the ASME world to this day, IMHO.:)
Frank

RE: Spinoff2: Using orientation to control position

Frank,
You are right!
The purpose of my example with 2-hole block was exactly that: To show that Orientation alone doesn't have enough power to compete with Position. Datum [A] is good enough for Perpendicularity, but to locate with precision you need complete framework; and I am afraid only in ISO Perpendicularity pins down position and only by mistake.
And bad news: there is no definition of "location" in Y14.5-2009
 

RE: Spinoff2: Using orientation to control position

(OP)
CH,
Thanks, I suspected that, so you never know. ;)
IMHO, The standard is wrong on concentricity, symmetry, runout, the adoption of ISO datums without conforming to ISO rules, common zone vs. continuous feature, anything else you want to add?
As you point out we all seem to agree the ISO was wrong in your cited instance. Of course the standards have the convenience of just defining themselves right. I was going to bring this discussion up in the discussion on the ISO issue, but I knew I needed my own thread.
FYI, I laid out the rough example pmarc had sketched earlier. I did not know if he had actually literally calculated those (2) bad part examples he showed. I get about a .060 position error translates to about .010 surface parallelism (we are missing a dimension for the depth of the keyway).
Frank
 

RE: Spinoff2: Using orientation to control position

(OP)
I have thought about it some more last night and had an epiphany of sorts. I am sorry, I cannot give up right to call this fact of containment a form of: "location" in a non-beginner crowd. Orientation does not control "absolute location" that is the kind or location you are all thinking of and concerned with. It does absolutely control the "relative location" of the other points of the feature so defined that is the kind of control that this relies on.
Frank

RE: Spinoff2: Using orientation to control position

Frank,

CH is right, there is no specific definition of "location" in Y14.5  We must pull its meaning from the context(s) it is used in.  Here is the breakdown that I would use:

1. Location of a feature relative to datum(s)
-we get this by applying any of the Tolerances of Location (Position, Concentricity, Symmetry) to a feature or features
-I would say that we also get this with both types of Profile, Circular Runout, and Total Runout
-location is controlled because the tolerance zone is not allowed to translate relative to the datum(s)
-the relationship between the considered feature and the datum(s) must be basic described with explicit or implicit basic dimensions/angles)
-I usually refer to this as "absolute location"

2. Location of a feature relative to other features
-we get this by applying the Position or Profile characteristic to a pattern or group of features
-location is controlled because the tolerance zones are not allowed to translate relative to each other
-the relationship between the features must be basic (described with explicit or implicit basic dimensions/angles)
-I usually refer to this as "relative location"

The use of the terms "absolute location" and "relative location" here is my own, and others may suggest alternative terms.  Also, directly toleranced dimensions can also locate features but I have not dealt with this case.

Frank, you're extending the idea of relative location to apply to the location of points on a feature relative to other points on a feature.  I would say that this is a valid concept, but the Y14.5 standard does not go there.  Using the term "relative location" to apply to within-feature relationships would confuse most GD&T users.

Can we agree to acknowledge that containment is technically a type of within-feature relative location, but reserve the term "location" to apply to features as described above?  

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

(OP)
Evan,
I hope you know I want to, but, don't all points have to be contained in a tighter orientation or form zone under ASME rules as you fundamentally understand it?  I really am misunderstanding ASME rule fundamentally if that is case!  How can we all say that an orientation tolerance will control form if it is not true?  Have we stumbled on the ASME's version of independency?
Thanks for getting me here!
Frank
 

RE: Spinoff2: Using orientation to control position

Frank,
Orientation tolerances are applied to the axis/centerplane of the "actual mating envelope," so that's why we can say they don't necessarily control form. Think of a bent cylinder.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

(OP)
JP,
Thanks, Thats right we now hace AME's! I was thinking and discussing surfaces here, all points on a surface are still forced to be contained in a zone, are they not?
Frank

RE: Spinoff2: Using orientation to control position

Yes, on a surface the form would be controlled.  Sorry if I threw in a curveball about the AME on a feature of size; I haven't been following the thread closely and wasn't sure if we were talking about surfaces or features of size.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

(OP)
JP,
Thanks, That was good for me, because, I need to flesh out this whole difference in an AME and an actual FOS better.  I am getting to the point where I would like to understand the differences in imparted control.
Concentricity still controls the actual center of a FOS, while the control imparted by the AME is tough to really conceptualize, is it not, or do you find it easy?
Frank

RE: Spinoff2: Using orientation to control position

Frank,

Yes, all points need to be contained in an orientation or form zone.  So when applied to a planar surface, an orientation zone will control form. I don't think anybody's going to argue that.

We (well, at least I) just don't want to apply the word "location" to the containment of points within any kind of tolerance zone.  The concept of containment is a fundamental paradigm in GD&T - every geometric characteristic requires that something be contained in a certain tolerance zone.  That something might be the entire surface, a derived point/line/plane, a surface element, or whatever.  The tolerance zone can have various types of constraints applied to it.  But there is always a tolerance zone, and something that must be contained within it.

It seems to me that the underlying, if unstated, concept of location in Y14.5 has to do with controlling translation of the tolerance zone:
-All geometric characteristics that control location constrain the translation of the tolerance zone in some way.
-All geometric characteristics that do not control location allow the tolerance zone to freely translate.

How does that sound?

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

"All geometric characteristics that control location constrain the translation of the tolerance zone in some way."
Boy, Evan -- why didn't you mention that in my other thread? I used a dozen different ways to claim as much, but people still want to allow weasel room for position to control only orientation.  :)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

J-P,

Sorry, I only came up with that description this morning as a result of pondering Frank's "containment" thing.  But the idea had been floating around somewhere in my head for a while - contained but not located, if you will. ;^)

Don't worry, I'm going to apply it to your other thread.  I think that the translation concept strengthens my case, that Position controls location even when applied to a single perpendicular hole.  But I might have to pull out some pretty abstract stuff to argue it.  Stay tuned.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

(OP)
As I mentioned what is important, is the result, not how I want to describe it. The establishment by framework definition places the keyway on center. The containment provided by the parallelism controls the sides surfaces to zones that are parallel to the shaft axis yet still allowed to float inside the greater size tolerance zone.
I mentioned above that a .010 zone controls position roughly .060 total position zone (.030 off center) in this case.
I am certainly curious if you believe this callout, pmarc kindly provided for me, is a logical extension of principles and legal and I never told you what I was doing with it.;)
Frank
 

RE: Spinoff2: Using orientation to control position

Frank,

I see it now, you and your inspector are correct.  It took 4 or 5 days to get over my preconceived opinion, but I finally see it.  I followed your logic about the framework and I agree with it now.

I humbly retract my earlier statements about pmarc's diagram.  The two imperfect as-produced part geometries shown would not meet the print.  The actual Parallelism error seems to be about 2 or 3, far exceeding the 0.05 tolerances.

It does appear that the Parallelism tolerances somehow indirectly limit the amount Position error that is possible.  I don't know if this qualifies as location control, but it sure mimics it pretty well.  This brings into question what type of geometric error pmarc's diagrams represent - is it location error, orientation error, or somehow both?

Thanks for sticking to your guns on this and not giving up on us.  I think that this is going to lead to an improved understanding, at least for me.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

(OP)
Evan,
I thank YOU for taking time to stick with me! You guys are about my only resource for this kind of stuff and I defiantly do not wish to ruin it. People come to me for answers on this stuff and if it is not in the book, I have to "make the call". The drawings we make are out there for all to see, we are not like doctors we do not bury our mistakes (just an old cliche):)
This was 20 years ago, now we might use the angularity symbol (under 2009) or maybe composite profile, profile was outlawed by a management dictate at the time.
Frank
 

RE: Spinoff2: Using orientation to control position

Frank,
I owe you an apology, and if we ever meet in person, a dinner, lunch, or a beer...  I sent an email to Evan directly today and his reply with "think of the simulator for datum feature B" hit me over the head firmly, so my feeble brain could finally see your point.  You are absolutely correct and I was quite wrong to mindlessly cite the common "orientation tolerance do not locate a feature"...  Except when they do, as you have very patiently continued to point out.

The datum feature simulator for B must be perfectly centered on a radial line from datum A (or, if it is a physical datum feature simulator, centered within tooling tolerance to that radial line)...  Using the 2009 terminology of "Regardless of Material Boundary" (RMB) the simulator for B will grow to fill the slot and as it does, any location error of the slot will cause the part to rotate about datum A until the simulator for B cannot grow any more...  This rotation needed to accommodate the location error of the slot may cause either or both of the sides of the slot to tilt out of their respective parallelism tolerance zone.  Because of this effect the parallelism tolerances on the side of the slot have indirectly controlled the slot's location relative to the datum reference frame [A,B].  I know what I've just stated is no more than what you've been saying, but I like to explain it using slightly different terminology.

So, I get the "closed mind of the month" award on this one.  Thank you very much for politely and patiently persisting with your point.  It is a very good one.

Dean
www.d3w-engineering.com

RE: Spinoff2: Using orientation to control position

I haven't really been following this thread, but based on the last two posts I said, "I gotta see what this is all about!"

Frank put it well when he said that location is controlled "through the back door."  I can see what he means, using pmarc's sketch: first we grab onto the OD to hold the shaft, but then we rotate it until the one side of the slot meets the datum B simulator.  That's the key: only one point of the slot's wall may hit the simulator, so now the rest of the slot will look angled, thus failing parallelism.

So having datum B on there does mean that we'll eventually discover if the slot's location is off center.  (I'm just saying all this to explain it to myself, really.)

Jim S. had a similar analogy with profile a while back, and it took time for me to fully buy it.  I claimed that a profile tolerance really shouldn't reference a datum that is part of the surface being profiled.  But the light bulb went on, and there may be a time when such a "self-datum" actually changes the meaning slightly.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

I promised to myself that I will not take part of this thread any longer, but now, when Evan, Dean and J-P have collectively agreed with Frank, I feel like have to jump back in and understand where did this sudden change come from.

I must admit, I have some difficulties in visualizing some of your statements, like:
Evan's: "The two imperfect as-produced part geometries shown would not meet the print.  The actual Parallelism error seems to be about 2 or 3, far exceeding the 0.05 tolerances."

Dean's: "The datum feature simulator for B must be perfectly centered on a radial line from datum A (or, if it is a physical datum feature simulator, centered within tooling tolerance to that radial line)..."

J-P's: "That's the key: only one point of the slot's wall may hit the simulator, so now the rest of the slot will look angled, thus failing parallelism."

It seems that the most crucial for understanding the case is to visualize how - based on my sketch - datum feature simulators A & B (or actually their mutual relationship) look like. Can someone of you enlighten me, please? A sketch would be perfect.

RE: Spinoff2: Using orientation to control position

Well, attached is a VERY crude sketch, but it is how I see the situation.

First, in your mind rotate the entire picture so that the gage plate representing datum B is at 12 o'clock.  Notice that this gage plate must be in line with datum axis A. Now, since our actual slot was off center, the shaft is rotated clockwise until we make contact with the gage plate.  My hand scrawled note will explain it from there.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

pmarc,

JP's sketch was a good start, here's one that goes a bit further.  I haven't shown the datum feature simulator for A - there's just a small dot to represent the datum axis.  But the sketch should illustrate the statements that were difficult to visualize.

The most important detail here is that datum feature simulator B is directly in line with datum axis A.  This isn't a trivial detail and is worthy of discussion.  I'll start this in another post.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

But Evan, on pmarc's drawing datum feature B was just the slot's left wall.  Otherwise, A-OK!

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

J-P,

That's not how I understood it.  In pmarc's drawing, the datum feature symbol is directly in line with the size dimension.  So I thought that datum feature B was the slot.  Those darn drafting-based rules!

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

pmarc,

The "back-door location" effect relies on the fact that the simulator for B is directly in line with the simulator for A.  In other words, simulator B is basically located to simulator A.  If this were not so, then the simulator could shift to accommodate the location/orientation error of the slot.  The end result would be that datum centerplane B would pass through datum axis A but be parallel to the unrelated AME of the slot.  Using this DRF, the mislocated/tilted slot would meet the print.

I am not sure where ISO stands on this, but basic location of simulators has only been required in Y14.5 since 2009.  See Section 4.5.2 on page 53:

Datum feature simulators shall have the following requirements:

a) perfect form.
b) basic orientation relative to one another for all of the datum references in a feature control frame.
c) basic location relative to one another for all of the datum references in a feature control frame, unless a translation modifier or movable datum target symbol is specified
d) movable location when the translation modifier or the movable datum target symbol is specified

But it wasn't this way in '94.  From what I remember, Y14.5M-1994 didn't make any explicit statements but certain figures indicated that the simulators were not basically located.  But Y14.5.1M-1994 spelled it out clearly, that lower-precedence datums were basically oriented but not basically located.  See Section 4.3.2 c) and Fig. 4-2 in Y14.5.1M-1994.  The geometry Figure 4-2 is very similar to the situation we are discussing in this thread, except that the slot is a tertiary datum feature.  But the method of clocking the DRF to the slot is clearly shown, and orienting the slot sides to this DRF would not give back-door location.

So Frank and his inspector are correct, but maybe they've only been correct since 2009.  ;^)  Again, the rule might be different in ISO and may have thrown you off.  Do you know how ISO handles this issue, pmarc?

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

Ugh,  I noticed that after my post!   You are right; the datum is the center of the slot, not the one wall.  
Add my name to the list of flubbers in this thread  :)

The 1994 standard does mention that a datum center plane such as our situation is to be in line with the previous datum.  It's in the text of Figs. 4-15 thru 17.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

Evan, J-P,
Thanks for your try, but I do not buy it. I mean, the explanation on why datum centerplane B must be in line with datum axis A does not convince me.

The figures you both are refering to are different from my sketch in one veeeeeeeeeeeeery important aspect: in all of them there is a locational relationship defined (i.e. positional tolerance) between slot's centerplane and higher precedence datum(s). If that was the case in my sketch reflecting Frank's dimensioning scheme I would not have any remarks and would never say to him that his interpretation was wrong.

But since nothing defines a relationship between datum features A and B, I do believe nothing constrains the translation of datum centerplane B to datum axis A.  

RE: Spinoff2: Using orientation to control position

J-P,

You're right about the datum plane being in line in '94, my recollection was wrong. Serves me right for relying on memory and not actually looking it up.  This was a direct contradiction between the math standard and Y14.5.  Major problem.  We'll have to make sure to remove things like that in the next version of the math standard, because they seriously affect its credibility and usability.

So Frank and his inspector were correct all along, unless you go with the Y14.5.1 meaning.  But who reads the math standard anyway? ;^)

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

pmarc,

So you're saying that a basic relationship between the datum features is not sufficient, that the relationship must be toleranced or we do not get the basic relationship between the simulators?  You might be right, but I'll have to think about that one.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

Yes Evan, this is what I am saying.  

RE: Spinoff2: Using orientation to control position

I'm not following this latest angle -- isn't it accepted that the simulator for datum B must come down toward the shaft while in line with datum A?    I understand that there is no tolerance on the location of the slot, but we are simply trying to simulate the datums in order to check the two FCFs.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

FYI -- if it helps, I'm looking a para. 4.11.4 (d) in the 2009 standard and 4.5.3 (c) in 1994.

It's interesting that the 2009 standard says that the simulator for datum B in our situation "must be oriented and/or located to the primary datum feature's datum feature simulator."

That whole thing about and/or might play into the different interpretation that pmarc is holding to.  I for one will try to noodle this thing again.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

pmarc,
Evan pointed out Y14.5-2009 section 4.5.2 already...  In that section the way to have the effect you describe in your sketch is provided...  Per sections 4.5.2 (c) & (d) the translation modifier would need to follow the datum feature B letter in the parallelism tolerance(s) applied to the slot.  Without that modifier there is nothing that I know of in the standard that will make the simulator for datum feature B anything but fixed and centered relative to datum A.

Dean
www.d3w-engineering.com

RE: Spinoff2: Using orientation to control position

Guys,
Please have a look at the attached sketch. In order to show my point as clear as possible, I modified Frank's part a bit; I removed both parallelism callouts and added two holes just to have datum B referenced somewhere on the print.

http://files.engineering.com/getfile.aspx?folder=78e400ef-6079-4ce5-874a-2afe47504df9&;file=keyway_parallelism_2.JPG

My questions are following:
- How will the datum feature simulators A & B look like for holes position tolerance check (especially mutual relationship of simulators) depending on the case?
- Will there be any differences amongst the three?  

RE: Spinoff2: Using orientation to control position

pmarc,
Could you loosen up some of the requirements?
The whole point could be lost when trying to control evrything at RFS. smile

RE: Spinoff2: Using orientation to control position

pmarc,

My first instinct is that the simulators will be an adjustable size sleeve and an adjustable size block, with the block being basically located to the sleeve.  There would be no difference for the 3 cases.  I do not know of any Y14.5 references that indicate that the simulators would have different mutual constraints depending on their tolerances.

At the same time, Y14.5 does say that the relationship between the datum features shall be controlled.  This was only a suggestion in Section 4.3.3 in 1994, but was much more strongly mandated in Section 4.9 in 2009.  Case #1 and Case #2 would not meet the criteria specified in 4.9 b), because they do not control the location of the secondary datum feature to the primary.

One could say that Case #1 and Case #2 are incomplete drawings anyway, because the location of the slot relative to the OD is not controlled.  But I'm wondering what the interpretation would be if this was controlled by a general Surface Profile tolerance.  Is that enough, or does there need to be a location control on B that references A?

Also, does the fact that datum feature B is referenced RMB make any difference?  It shouldn't, but if datum feature B was referenced at MMB then the relationship between the datum features would have to be more clearly defined.  Otherwise, the MMB and simulator size could not be calculated.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

For Pmarc's scenario:  
Case 3 is the easiest -- a datum feature simulator must be in line with axis A as it comes down. This is clear from the standard (Fig. 4-15) and there is a basic relationship between A and B.

I suppose Cases 1 and 2 would be the same simulator for each other, because they both do not have GD&T to locate the slot to A.  However, the location is implied to be in line with axis A.  So the million-dollar question is: what is the tolerance on that implied side-to-side location?  Title block? That could be dicey if the title block separates the tolerances by the number of decimal places.

So perhaps 1 and 2 are unclear drawings (as is the original one that started all this), because the relationship between the datum features is not complete.  Here's a similar analogy:  In Fig. 4-20 (c) of the standard, what would be the size of the datum feature simulator for A if there were no perpendicularity tolerance given?  It wouldn't be 16.0. There has to be some tolerance on the orientation in order to properly describe the simulator for B in Fig. 4-20.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

Evan, J-P,
Of course, cases 1 & 2 are incomplete by intent. I just wanted to know whether in your opinion datum feature simulators A & B were the same for all 3 cases or not. I see that you agree they are the same.

My last try: what about implied basic zero dimension between axis of datum feature A and the centerplane of the slot B? Does it apply here [based on of 1.4(k) of Y14.5-2009] or not?

RE: Spinoff2: Using orientation to control position

Pmarc, I kind of see what you're saying.  There is an implied zero relationship between A and B, but it's not basic, since no location tolerance is given to necessitate a basic dim.

But that's the point; the drawing is incomplete, and thus our whole dilemma is unanswerable, in my view.  See my analogy about Fig. 4-20, if there were no perp tolerance.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

J-P,
And that was also my point regarding Frank's example. Like I said in my post from 5 Feb 12 12:37: "The figures you both are refering to are different from my sketch in one veeeeeeeeeeeeery important aspect: in all of them there is a locational relationship defined (i.e. positional tolerance) between slot's centerplane and higher precedence datum(s). If that was the case in my sketch reflecting Frank's dimensioning scheme I would not have any remarks and would never say to him that his interpretation was wrong."

Since Frank's dimensioning scheme is incomplete (i.e position tolerance is missing) I cannot understand why you, Evan and Dean are saying that datum feature simulator B is fixed in location relative to datum feature simulator A.

And yes, I agree with you when you are refering to 4-20 and a potential lack of perpendicularity callout. Paragraph 4.9 is very specific on that.

RE: Spinoff2: Using orientation to control position

pmarc,
The presence or absence of tolerances on the datum features has no bearing upon the requirement that datum feature simulators be "perfectly" oriented and located with respect to each other...  Unless you apply a sliding modifier per Y14.5-2009, the simulator for the slot, datum feature B, must be aligned with datum A.

Dean
www.d3w-engineering.com
 

RE: Spinoff2: Using orientation to control position

Okay, I am out of bullets. But at least my reply is #100. smile

RE: Spinoff2: Using orientation to control position

Dean, I don't have the standard in front of me, but does it really say that the datum feature simulators must be perfectly located to one another?

We all know about the "mutually perpendicular" requirement, but that's perfect orientation. I'm itching to see if it says perfect location.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

(OP)
I thank you all again for going through this.
This was 20 years ago, technically, we should be asking what it would mean under the 1982 standard. Any part drawing that I am aware of that used this scheme would have been referencing that.

Dean,
Thank you.

CH,
Is pmarcs' issue the same problem you had too when you proposed A-B, I never really understood where you were going there?

pmarc,
I think your question is now whether the "theoretical gages" we conceptually use to establish these things are allowed to be perfect or based on an "image of perfection". I admit, I have always thought this was an oversimplification by the standard too, but I believe it is one ASME has been making since the beginning.
This "image of perfection" gaging concept was the way it explained in 1982 and if 1994 has made statements that undercut that then, for me, it will serve as another example of the standards being inconsistent with their own logic. Then if, 2009 makes statements to bring it back, it sounds more to me like someone made a temporary mistake. What was the actual concentricity between the (2) A-B collets used to inspect runout? What is the tolerance on the 25mm basic offset datum A established under the offset datum section? What is the tolerance of datum targets relative to each other? What is the tolerance on a basic dimension in the first place? These examples and concepts are based on the same 'image of perfection" and have been shown consistently throughout the different versions of the standard all with small text caveats saying in essence: "if it matters, it might matter". Kind of like the ISO saying: "if the part is out of tolerance but it works the part is OK", seems like they are all "hedging their bets" to me.
Frank

RE: Spinoff2: Using orientation to control position

J-P,

It really does say that. The simulators must have basic location, at least in 2009.  I don't have the standard in front of me either, but I referenced the section earlier in this thread.  See my post from Feb 5 at 10:39, Section 4.5.2 c).

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

Doh,  thanks Evan.   Sounds like case closed (presuming the appropriate standard is referenced).  Sorry I doubted you, Dean  :)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: Spinoff2: Using orientation to control position

fsincox,
About A-B.
I cannot make a good picture right now, so I'll try to explain it verbally. Please try to follow.
Datum A derived from Diameter is an axis, just a line in space; you cannot locate your keyway from just one line, it's against basic mathematics, no matter front door or back door.
Datum B is plane, derived from keyway, floating somewhere in space. You guys just proved brilliantly that nobody knows for sure how A is related to B. Lets agree that even if datums have to be located perfectly, datum features have not, until you explicitly specify relation thru FCF.
Datum A-B in my understanding is plane, located as close as possible to BOTH centroid derived from diameter and centroid derived from keyway. There is only one plane like that, even if it's not perfectly located in space.
Now when we try to control sides of the keyway to plane A-B thru Parallelism or even Angularity, the tighter is the tolerance the closer we are to perfect keyway.
I think this discussion was already long enough, so I kind of slowed down. It is not like I lost interest.
 

RE: Spinoff2: Using orientation to control position

(OP)
CH,
Are you opposed to more? I actually did have a point to all this and was debating whether it should be a new post or continue. It actually will be along the same concept you proposed in a way. I see the shaft and key as more of a primary-secondary kind of relationship. After the discussion I realized that you may have thought that the use of coequal datums was a way to get around this whole, "but B is not located to A"  bit. How can they argue with A-B it is done all of the time, I agree but it whit the argument, but, it does not agree with actual function IMHO.
I really am not trying to tear everything down and start all over as some may like to think. I am just trying to get them to be consistent and live by their own rules, it is supposed to be a standard after all.
Some think standard means force all to do it this way, I think standard means provide a consistent set of tools to use to get any needed job done.
I would like to find a way to contact you if we could, not sure how to do that though?
Frank

RE: Spinoff2: Using orientation to control position

Thank you Frank,
I was under impression the thread is coming to logical conclusion.
Most people agreed that under some conditions Orientation may serve "quasi-positional" purpose.
You mentioned yourself that Position would be your first choice, so I was seeing the whole thing as secondary "back-up plan" rather than mainstream solution.  Maybe I was wrong.
In my experience in today's world even simple textbook solutions (not to mention more "exotic" approaches) have to be shown down one's throat, so keeping things simple should be priority.
Nevertheless I will be happy to join "spin-off" dedicated to any of 15 (or whatever) GD&T symbols. smile
 

RE: Spinoff2: Using orientation to control position

I'm not done talking about this.  The horse is not quite dead yet ;^).  I think there is something in the peculiar geometry of the shaft and keyway.

I was trying to think of other applications in which the "back-door location" technique would be possible.  One of them was controlling a cross hole to be centered on the axis of a shaft.  Another was controlling a cylindrical hole to be centered on a spherical feature.

In all of these applications, we're trying to "aim" something at a target that is in the middle of something round.  The interesting thing (to me) is that the distinction between orientation error and location error becomes blurred.  If I'm shooting at a target and I miss, I can describe the problem in two ways:

1) I aimed in the wrong direction for where I was standing.  I can correct the problem by standing in the same place but aiming at a different angle.

2) I was standing in the wrong place for the direction I was aiming.  I can correct the problem by aiming in the same direction but moving to a different place.

Description 1) amounts to orientation error, and description 2) amounts to location error.  It's two different ways of describing the same error, so we could control it in two different ways.

Does that make any sense?

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Spinoff2: Using orientation to control position

(OP)
Evan and CH,
Basically I think the same effect that we have been discussing here, is the same effect that makes runout work. Yes, the runout I find somewhat useless as a concept and is supported by the ASME most likely only because it is a popular inspection method.(sorry guys, particularly Dingy3, I know he loves it so).  I am not really trying to take his favorite method of inspection away, though some who may want to simplify might.
John Liggett proposed a simplification of GD&T in a Machine Design (Aug 20, 1992) article, in it he refers to runout as an orientation tolerance. Early ASME versions placed runout under tolerances of "form and orientation". Taking an indicator and running it across a surface is normally an orientation (parallelism) check, it is the particular special datum set up and rotation that forces location control. I suspect that is related to the effect going on here. In essence the particular datum framework establishment controls location with an orientation tolerance!
 So if you will insist it is OK to not control the axis in runout why do you want to worry about it on the slot? Let's be consistent at least, I think the same uncomfortable feeling you get about the slot not being located is exactly the same feeling the ISO and I feel about runout vs. concentricity!
Frank
 

RE: Spinoff2: Using orientation to control position

CheckerHater,
For your datum A-B description, the datum feature simulators for A and B are perfect, or built with tooling tolerance, so relative to the part, they can be considered perfect.  All the same for A as primary and B as secondary...  Datum A is the axis of the datum feature A simulator and datum B is the center plane of the datum feature B simulator.  Datum A-B would be a line on a plane, with the only degree of freedom remaining being translation along the line (see Y14.5-2009 Figure 4-3(f)).  The line would be the same as datum axis A and the plane would be the same as datum axis A.

All the difference between [A,B] and [A-B] comes when the datum features are mated with their simulators...  For the [A,B] case the simulator for A first grows material until it constrains datum feature A as fully as a perfect cylinder can, then the simulator for B grows material (using Regardless of Material Boundary, as with A) to constrain rotation about datum A.  For [A-B] the two simulators grow material simultaneously and each will continue to shrink in size until they constrain the datum features as much as they "do"...  I say "do" because there is currently a discussion within and between the Y14.5 and Y14.5.1 committees to resolve whether the second simulator will continue to shrink around its datum feature after the other has engaged the datum feature to the point that it cannot shrink any more.  With any "A-B" type of case with features of size this is a point that needs clarification in the standard.

With A-B the slot has an equal influence to that of the cylindrical feature for constraining one of the rotational degrees of freedom that the cylinder as a primary would have first influence over...  This makes A-B pretty difficult to handle correctly for most inspection methods that I am aware of.

I wouldn't recommend A-B for this type of part.  For this discussion and to better model the most common functional cases for this type of part, I think A as primary and B as secondary is better.

Dean
www.d3w-engineering.com
 

RE: Spinoff2: Using orientation to control position

Dean,
OK, [A] simulator is a chuck or collet.
How you visualize [B] simulator and its relation to A?

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