Parallelism on per unit basis
Parallelism on per unit basis
(OP)
Hey folks,
Another question has come up. I found another thread on this subject but didn't find a definitive answer in it. I don't find direct support for parallelism on a per unit basis. This seems to be a legitimate extension of principle but I'd like to get others opinions or maybe point me to the place in the 2009 standard where it exists. In reality we'd like to add a tangent plane modifier to it but that shouldn't make a difference in the answer.
Thanks,
Another question has come up. I found another thread on this subject but didn't find a definitive answer in it. I don't find direct support for parallelism on a per unit basis. This seems to be a legitimate extension of principle but I'd like to get others opinions or maybe point me to the place in the 2009 standard where it exists. In reality we'd like to add a tangent plane modifier to it but that shouldn't make a difference in the answer.
Thanks,
Powerhound, GDTP S-0731
Engineering Technician
Inventor 2010
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II





RE: Parallelism on per unit basis
No, there isn't direct support for it in the standards, however it is a logical extension of principles. A friend of mine uses it in the armaments industry and advocated for its inclusion in the '09 release of Y14.5. Unfortunately there wasn't enough support for it to go forward at that point. There was no valid argument posed against it either, and many of us recognized the value.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Parallelism on per unit basis
I was really beginning to think that the question was so stupid that no one wanted to dignify it with an answer...lol.
Powerhound, GDTP S-0731
Engineering Technician
Inventor 2010
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Parallelism on per unit basis
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Parallelism on per unit basis
Flatness per unit is a refinement of flatness.
If your Parallelism does not specify surface smooth enough, you add Flatness.
If Flatness still not smooth enough you apply flatness per unit.
Why not use existing controls before creating your own by “extension of principles”.
To me the reason ASME is not in the hurry to extend the principles is that there is no need to re-invent the wheel;
So I am intrigued: What exactly ‘Parallelism per unit” will achieve that Flatness cannot do?
RE: Parallelism on per unit basis
Technically, Flatness or Flatness per unit will create a tolerance zone that can be at any angle to datum plane (within "global" Parallelism tolerance zone, of course), which is not the case when Parallelism per unit is used. So from purely geometrical point of view there is a difference.
Notice also that powerhound actually wants to apply tangent plane modifier to those callouts, so to me it seems that he is not interested in controlling Flatness at all.
RE: Parallelism on per unit basis
What pmarc said is correct. It's the tangent plane that is important in this case. Thanks for the lesson though.
Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Parallelism on per unit basis
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Parallelism on per unit basis
RE: Parallelism on per unit basis
RE: Parallelism on per unit basis
This is exactly my question:
How you establish TANGENT plane if your single unit spot falls within CONCAVE area?
Is your mathematic somehow different from my mathematic?
RE: Parallelism on per unit basis
Now check the parallelism of the flat plate. Done!
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
Even a concave area has got the highest points at the boundaries of the per unit area. They could be used to establish the tangent plane.
I would be rather worried if the local area was convex, so the tangent plane could freely rotate around the peak.
RE: Parallelism on per unit basis
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Parallelism on per unit basis
Could you elaborate on your last comment? I am somehow confused by what you said - of course assuming that I understood it correct.
RE: Parallelism on per unit basis
Sorry, but I don’t buy it.
I suggest opening book on geometry (please, no Wikipedia) and reading definition of tangency from there.
I am out of this.
RE: Parallelism on per unit basis
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Parallelism on per unit basis
I would not want to go into maths with that. Maybe you are right, maybe the definition of tangency is different to how I and J-P see it. However Y14.5 clearly says it is "a plane that contacts high points of the specified feature surface" (para. 1.3.45). In the light of that I do not think there is anything illogical in our earlier statements.
Jim,
The tangent plane, as a verified entity, is not related to any datum referenced, the parallelism tolerance zone is - at least this is how I see it.
RE: Parallelism on per unit basis
I suggest opening the ASME standard and reading the definition, as well as studying the illustration, of tangent plane from there since that's what we're actually talking about. We aren't talking about geometry.
The tangent plane of a surface, as far as GD&T is concerned, is formed by the three highest points of that surface. This is where a plane is tangent to all three of them simultaneously. That is the plane that has to be parallel to the datum
Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Parallelism on per unit basis
http://www.tec-ease.com/gdt-tips-view.php?q=218
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Parallelism on per unit basis
I agree with the tip; however, it is using a basic dimension along with a profile of a surface callout. That is not the same as using parallelism with a toleranced dimension.
Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Parallelism on per unit basis
I do not think the tip proves that tangent plane is oriented wrt the datum references. Actually it clearly says that the tangent plane is established by high points of the feature. This plane is simulated by surface of flat plate and that surface must lie within tolerance zone that is oriented (and in this case also located) wrt datums.
RE: Parallelism on per unit basis
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
Pmarc, Belanger, Powerhound
Yes, indeed, it is about geometry
RE: Parallelism on per unit basis
Cut off everything that is on the left and on the right of the local area, and the one that you are saying is not tangent will become tangent. Not tangent in geometrical understanding, but tangent in a way that the plane will be contacting the high points of the surface within considered area. Again, forget about math, just follow Y14.5.
J-P,
Yes, this was exactly my point.
RE: Parallelism on per unit basis
And where exactly Y14.5 supports your interpretation?
RE: Parallelism on per unit basis
RE: Parallelism on per unit basis
Pmarc,
I didn’t find where it mentions “surface within considered area”, only the entire surface.
Illustration doesn’t show it on “per unit basis” either.
Y14.5-1 is no different.
About being “rather worried if the local area was convex”, I may assure you that your “plate” will rock anyway on either convex or concave surface, because there is no guarantee that surface will always match all 4 corners of your 1 x 1 area. So why not to extend principle even further and specify 1 x 1 x 1 triangular zone?
Let’s face it: Parallelism per unit basis is not supported by the standard. There might even be a reason for that.
Also, Parallelism when specified with Tangency does not automatically control Flatness, so it is only natural to add separate Flatness control, if you are worried about your surface being smooth.
To me Parallelism per unit makes as much sense as applying Tangent requirement to Flatness. Could that be considered “extension of principle”?
I also liked how you changed your argument from “from purely geometrical point of view there is a difference” to “Again, forget about math”. Well, whatever helps you thru the night.
Sorry, I promised to get out of this argument, but someone woke up my inner jackhole.
RE: Parallelism on per unit basis
1. We have a 48 X 48 base plate.
2. On this base plate sits a 20 X 20 plate with the functional assembly mounted to it.
3. All I care about is that the 20 X 20 plate sit parallel within .005 to the datum plane which is established by the bottom of the base plate.
4. There is no reason for the entire 48 X 48 surface to be parallel within .005 to the datum plane.
5. There is no reason any part of the surface to even be flat within .005.
I feel that the tangent plane modifier on parallelism is a logical extension of principle for this situation.
If there is a way to do what I'm trying to do that doesn't require an extension of principle like this, please clue me in. I'm all for using the available tools in the standard.
Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Parallelism on per unit basis
Tangent plane on parallelism is not extension of a principle, it is standard.
Parallelism per unit is not. But you can add flatness and /or surface roughness to demand your surface to be as smooth as possible.
It looks to me that you are just fine.
Sorry for unnecessarily heating up the discussion
RE: Parallelism on per unit basis
This all reminds me of another thread from this past January where we debated the meaning of 2D and 3D relative to profile of a line -- including discussions of topology and references to obscure math definitions. Shrug.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
But it's just the tangent plane within the local area that you've defined by virtue of the size of the small plate sitting down in there. That's the meaning we've been trying to say is probably OK, though not spelled out in the Y14.5 standard.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
No, it is not.
I would agree on the opposite, that part is tangent to the highest points of plate, but it’s not the same; it’s like swapping datum and related feature.
And why am I arguing anyway? I already have ANSI / ASME on my side
RE: Parallelism on per unit basis
I will try to answer to some of your statements/questions, though I have a feeling this will not convince you even a bit (but well, it wouldn't be me, if I hadn't try):
You could not find it because it is simply not there. How can "extension of principles" be defined in the standard? If it was there, it would not be "extension of principles" but a rule.
The surface does not have to match the corners. The surface has to rest on at least 3 high points. And it will always rest on at least 3 points - the problem is that those points may not always be the high ones. As for convex surfaces, it is interesting that both sources - the standard (para. 6.5) and the Tec-Ease's tip - make remarks that for this type of surface tangent plane concept has to be treated with some kind of caution.
No, it couldn't. Tangent plane, by definition, is perfectly flat, so Flatness requirement would be useless, illogical, illegal or whatever you want to call it.
Flatness or Flatness per unit tolerance zone is not tied in rotation to anything. Parallelism or Parallelism per unit tolerance zone is always parallel to datum plane. This is why I said that from purely geometrical point of view there was a difference. And I stick to it. If you do not like the wording, change it to "Y14.5's point of view" or "my point of view". I do not care. The clue was: "THERE IS A DIFFERENCE". No offence, but in my opinion you are simply nitpicking on a single word which isn't really crucial for the meaning of my response. You are just attempting to make it important for the purpose of proving that I am wrong or inconsequential. (Or maybe for the purpose of hiding that you are incapable to admit you are wrong in this case :-])
RE: Parallelism on per unit basis
If you take the large block in your sketch and slice it down to a block of only the smaller size, then can we discuss a tangent plane? If so, what's the difference if all the other stuff on the block is still connected to that local area?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
As I was looking over CH's graphic, I see it as a great support for "per unit area" application. Again, I know that it is being used in practice already, and it is very practical and necessary for the application.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Parallelism on per unit basis
A tangent modifier can be applied for an entire feature or for the incremental control that a "Unit basis" tolerance provides. Any issue with a tangent plane for an incremental portion of a feature could also exist for a tangent plane from an entire feature.
Dean
RE: Parallelism on per unit basis
Pmarc,
And you call ME nit-picking? I just noticed that you embraced math when it suited you and then threw math into the window both in the same forum.
And about admitting being wrong; everyone is entitled to their opinions.
I am simply in agreement with the guy who happened to say:
“ASME Y14.5-2009 also mentions only about flatness & straightness applied on a unit basis.
My opinion is that only these two controls can be applied with this concept at all. I can imagine a lot of difficulties in correct interpretation of such concept when it is applied to a geometrical tolerance that has got any datum reference (e.g. parallelism, runout or whatever).”
I am not hiding anything.
RE: Parallelism on per unit basis
Of course everyone is entitled to their opinions, no doubt about it. After all, this is what this forum is for.
And believe me, I truely respect your opinion.
I have just one more question to you, if you don't mind:
If you agree with the opinion of the person you cited, could you tell me/us what are these "difficulties in correct interpretation of such concept when it is applied to a geometrical tolerance that has got any datum reference"? I think this is the clue here. I have an impression that so far we have not heard from you any argument that would really support the statement. I am not telling that there are no difficulties at all. Maybe the difficulties are so serious that the concept indeed cannot work with characteristics other than flatness or straighntess. I would simply like to hear about those difficulties from you.
RE: Parallelism on per unit basis
That said, I don't see a problem with it from a theoretical point of view, so I agree that it's a valid extension of principles. But do consider the practical issues that may arise.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
Shortly, why applying parallelism per unit is troublesome:
1. It’s illegal both in ASME and ISO to begin with.
2. Flatness and parallelism are already misunderstood and often used interchangeably (not always correctly).
3. Hard gaging is simpler for “datumless” controls where feature is measured against itself.
4. CMM programs do not always follow standards as they are, not to mention extensions.
5. After you overcome all of the above the result is still useless as you must specify “global” parallelism anyway to avoid accumulation, and flatness will provide better control to prevent abrupt surface changes (BTW, it will not prevent, but merely reduce them)
We are not talking about tangent per unit here.
RE: Parallelism on per unit basis
1. Not true. Nowhere in Y14.5 it is said that it is illegal. Please point me to the statement saying so.
ISO 1101, 1983 edition, actually showed parallelism per unit callout as an example of callout containing a refinement in lower segment of FCF. In next editions of the standard (2004, 2012) it was replaced by straightness callout, however in my opinion that does not mean it is forbidden. Actually with the lack of a direct ISO standard on parallelism, I do not think we can judge whether it is still legal or not.
2. That proves nothing. Even assuming that both per unit characteristics are clearly and precisely described in the standard, there is always a place for misunderstanding and a risk that someone will apply it interchangeably. Similar to ASME's position and symmetry. Both are clearly defined in Y14.5, but still lots of folks use symmetry instead of position without awareness about differences between the two.
3 & 4. Again proves nothing. You focus on inspection method, not on the pure meaning of the characteristic. The fact that certain method is not suitable for checking a characteristic does not mean that there is no other method able to verify it. Actually I am curious how you imagine verifying even a typical parallelism callout by a hard gage.
5. Am I missing something or there was at least one vote here stating that unit basis parallelism worked very well in the application field? And I do not think we were ever talking about getting rid of "global" parallelism. Per unit parallelism should always be applied as a refinement of "global" callout.
RE: Parallelism on per unit basis
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Parallelism on per unit basis
1) Where does ASME Y14.5 say that it is illegal?
2) So what if people misunderstand the two? Let's get them to learn GD&T, rather than dumb down a print to suit the folks that aren't getting it.
3) Not sure why you think this. Parallelism is probably easier to measure than flatness, because you can simply set the part on an inspection plate and then run a height gage across the top. To check flatness involves carefully leveling the part first, or else drilling a hole in your inspection plate (!) to mount a dial indicator through the bottom. Also recall that circularity is also "datumless," yet it is one of the more difficult controls to measure.
4) So what? Let's get the CMM people to learn the proper rules, or let them go out of business.
5) It was assumed that the per-unit parallelism was already refining a parallelism tolerance. Plus, the size dimension would already have been controlling parallelism.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
1. Not true, plain and simple.
2. This is not a good reason to change something legal into something haphazard.
3. How would you hard gage a parallelism callout anyway?
4. Another bad reason to change anything.
5. Per unit specification allows for using a maximum value overall.
Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Parallelism on per unit basis
Per unit parallelism DOES NOT EXIST either in ISO or ASME. Prove otherwise.
Checkers...
RE: Parallelism on per unit basis
Do you even know what an extension of principle is? If so, have you ever used it? If you have, what was the application? I'm interested to know how you justified using it since your exact application of the principle would not have been shown in the standard.
http://www.tec-ease.com/gdt-tips-view.php?q=128
This tip shows how concepts shown in the standard can be used in ways not specifically in it. See "EACH ELEMENT" and the application of the between symbol for starters.
Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Parallelism on per unit basis
Are you ready to defend the notion that anything not stated in the Y14.5 standard is automatically illegal and thus absolutely forbidden?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Parallelism on per unit basis
Powerhound,
Principle: what you think you know for sure.
Extension of principle: what you make up when you don’t know the answer.
If you have better definition please educate me: is it somewhere in ASME standard?
Belanger,
There is no need to prove negative – it’s logical fallacy.
MechNorth,
“Per unit” by itself is extension of principle – it is not supported anywhere in ASME Y14.5.1M-1994. I am waiting for new edition.
What I mean (and I stick to it) that there is absolutely nothing in ASME Y14.5-2009 to support your point of view. Please take a look:
Section 5 Tolerances of Form:
Para. 5.4.1.3: “Straightness may be applied on a unit basis as a means of limiting an abrupt surface variation within a relatively short length of the feature.”
Para. 5.4.2.2: “Flatness may be applied on a unit basis as a means of limiting an abrupt surface variation within a relatively small area of the feature.”
In both cases method and its limitations are clearly described in writing, with appropriate illustrations. No other geometrical control has “unit basis” attached to it, not even any other Form control.
Section 6 Tolerances of Orientation:
Para. 6.5: “Where it is desired to control a tangent plane established by the contacting points of a surface, the tangent plane symbol is added in the feature control frame after the stated tolerance.”
And later (in small print):
“NOTE: The tangent plane symbol is illustrated with orientation tolerances; however, it may also have applications using other geometric characteristic symbols where the feature is related to a datum(s)”
This is what you call “an extension of principle”: tangent requirement may be used with other controls, even if it is not described in detail or illustrated in the standard.
So far standard is well thought-off and balanced: Unit basis is applied to controls without datums (and not even all of them). Tangency is applied to controls “where the feature is related to a datum”.
Nowhere in the standard there is a mention of mixing two together.
Now short “Executive summary” for those not reading long posts:
1. Straightness MAY be applied on a unit basis
2. Flatness MAY be applied on a unit basis
3. Tangency MAY be applied to parallelism and other orientation tolerances.
4. Tangency MAY be extended to other controls where the feature is related to a datum(s)
5. Anything else is figment of your imagination.
I have no much interest in arguing with people in denial.
Now I am very curious about the eye-opening experience, the epiphany that made pmarc change his opinion to exactly opposite.
So far his logic is a bit flawed: “ISO 1101, 1983 edition, actually showed parallelism per unit callout as an example of callout containing a refinement in lower segment of FCF. In next editions of the standard (2004, 2012) it was replaced by straightness callout, however in my opinion that does not mean it is forbidden”
Let say, if I get rid of my Ford and buy a Chevrolet; it doesn’t mean anything; I am still a Ford owner. Convincing.
So pmarc, your current opinion is exact opposite of what you expressed in this forum:
http://www.eng-tips.com/viewthread.cfm?qid=269210
What happened? Apparently you‘ve learned something I have no idea about. Please share.
RE: Parallelism on per unit basis
I have said to myself that I will no longer take part of this discussion, however in this case I have to reply.
Yes, I changed my opinion about legality of parallelism per unit area through all these years, and now I am saying it is perfectly applicable as an extension of principles. What is wrong with that? At least I was willing to understand the whole concept and was open for that change.
I will repeat again: throughout the thread you have not presented a single logical argument that would prove the parallelism per unit or parallelism per unit modified by T could not be used in real life application. By "logical" I mean, a sketch or a description that would defend your standpoint. Instead of that you are using some quasi-logic arguments in order to prove that we are mistaken and not that you are right.
RE: Parallelism on per unit basis
No need to be offended. You said that you changed your mind about the issue over the years.
So, what kind of evidence did you find over those years that convinced you? May be it will convince me?
So far it was you who didn’t offer any proof. At least I uploaded some sketches.
Here is another sketch, just for you.
RE: Parallelism on per unit basis
You can prove, as in provide the evidence, that something happened sometime someplace (kind of like they do it in court).
Can you prove that nothing happened?
This is what I mean by “negative” and this is why you are assumed innocent until proven otherwise.
So it is not my job to prove that anything not in the standard is automatically forbidden.
It is your job to prove that something not in the standard is automatically permitted.
In my post I mentioned small-print note that allows extension of tangency principle to tolerances that reference datum(s). I can cite that note to defend my decision to use tangent profile or tangent position (hey, it’s extension of principle).
What do you have to show?
RE: Parallelism on per unit basis
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
And I do not need to prove anything - the other guys' words (Dean's, Jim's and his friend's) speak for themselves.
As for what convinced me to the concept - I simply started to look at Y14.5 standard from wider perspective. It is simply impossible to gather each and every tolerancing case within a ~200 pages book. I learned that if something is not in the standard, that does not automatically mean it is illegal. If a concept is not in obvious conflict with the letter of the standard, I see no reasons to reject it just like that. Parallelism per unit area or parallelism per unit area modified by T are just the examples.
PS.: I am pretty sure you know that too. I am just surprised that you act so against it.
RE: Parallelism on per unit basis
Yes.
I will present my argument later - after all I am supposed to be working right now.
RE: Parallelism on per unit basis
I'm really trying to see your point but your drawings are leaving me in the dark. It makes me think that we are arguing two different things. I have no idea what your most recent drawing is trying to say. It's almost like you're trying to teach us what tangent is. I'm sure not confused about that. I know what tangent is and I know what the Y14.5 definition of a tangent plane is; so, why are you providing drawings that show things that are tangent and things that are not tangent? I really don't think anyone is confused about any of it. From what I'm gathering, the sole disagreement is whether or not Parallelism per unit, with a tangent plane modifier, is okay to do.
I noticed that you made no comment on the tip. I guess Don is either confused or just making things up too. You should give him a call and correct him and make drawings of tangent and non-tangent lines so he can realize the error of his ways. You claim that we're just making this stuff up but your asinine definition of extensions of principle is the most blatantly made up thing on this thread so far. You claim we're all in denial...whatever. It reminds me of the famous Joe Walsh lyrics "It's tough to handle this fortune and fame, everybody's so different, I haven't changed."
Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Parallelism on per unit basis
The concept of "extension of principles" is accepted by the writers of the ASME standards; it is why the section on Profile (for example) has grown so significantly in '09. It wasn't that people suddenly thought "hey, let's do this just because"; they brought the new material to the table based on what was already happening on industry, based on how significant companies and advanced thinkers in the field of GD&T had extended the principles. Look at composite profile tolerances for a pattern of features; it extended from composite profile controls on individual features, melded with the use of composite position controls for patterns of features. It was an extension of established principles, now an accepted principle.
Unfortunately, the sad reality is that if someone does not believe in the premise that extension of principles is the act of filling the great unknown, then there is no argument that will change the mind. I journey into that realm whenever I have to, and so far that's been more than a half-dozen times. Perhaps you have been fortunate enough to not need to push the boundaries, or perhaps you were guided to trade off functionality for simplicity. For whatever reason, you are evidently not willing to accept the concept of extending principles into new realms, at least for GD&T.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Parallelism on per unit basis
Attack the argument, not the person. Keep this on a civil basis. Certain words convey tone and insult, and are inappropriate in a technical discussion.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Parallelism on per unit basis
Powerhound,
Quote: “why are you providing drawings that show things that are tangent and things that are not tangent? I really don't think anyone is confused about any of it”
You did not read the thread carefully. In fact, people disagree with my definition of tangent.
Quote: “I noticed that you made no comment on the tip. I guess Don is either confused or just making things up too”
If you are talking about “EACH ELEMENT” note, it is straight from the book, together with “SEP. REQUIREMENT”, etc., etc. – nothing new. Call me when Ron promotes parallelism per unit.
You don’t like my definition of “extension of the principle”? I haven’t seen better from anyone on this forum so far.
Yes, I believe “extension of the principle” is totally made-up concept, which belongs next to “industry standard” – something to say when you have nothing to say – except profanity.
MechNorth,
You provided wonderful example; I just don’t believe the new definition that made it into 2009 was simply added because somebody decided to make-up stuff as they please; there must be some other procedure in place.
Belanger,
OK, I will try to convince you that you actually have to stick to the book.
Enter Para. 3.1: “Symbols should be used only as described herein”
To me interpretation of this paragraph is that making up your own symbology other than shown in the book is forbidden.
What to do if it’s “impossible to gather each and every tolerancing case within a ~200 pages book”?
I could be wrong, but I think 1966 version was simply saying that you can use either symbol or verbal description. Today it’s more “legalese”
Para. 3.2: “Situation may arise where the desired geometric requirement cannot be completely conveyed by symbology. In such cases, a note may be used to describe the requirement, either separately or to supplement a geometric symbol.”
So you can make-up stuff as you please, as long as you explain it on your drawing in form of a note.
In fact, I believe that by “extension of the principle” you can create your own control, say, “crookedness”, as long as you explain it on the face of the drawing “either separately or to supplement a geometric symbol”.
This is why my interpretation of the rule is: “If it’s not in the book, it is your job to explain it on the drawing”.
And this is why I strictly oppose the idea of symbology that looks “very similar” or “self-explanatory”. Nothing is self-explanatory.
I am standing by my list posted 20 Aug 12 7:32, I just didn’t have time for extensive explanation.
This forum is full of horror stories about shop “not getting” GD&T. Imagine the best possible situation: shop that invested into standard book and studying it. Your best bet will be for them to understand “by the book” examples; something not shown in the book will raise questions.
Same story with CMM – several posts mentioned CMM software not following established GD&T standards. Once again –your best bet in the perfect world is for software to match the book, not what’s left outside of it.
So if everybody will suddenly experience the need in parallelism per unit basis, let them explain on the drawing exactly what they need. Then it will probably make it into next Y14.5 – sometimes in 2025.
Hopefully I will be retired by then.
RE: Parallelism on per unit basis
You missed what I was trying to point out on the tip. Yes, all those things are in the standard. Parallelism is also in the standard, per unit tolerance is in the standard, and tangent plane is in the standard. Our argument is that since parallelism is not shown with per unit tolerance in the standard then you say it isn't a valid callout. The tip shows EACH ELEMENT, and the "BETWEEN" symbol both associated with a position tolerance. You will find all these principles in the standard but you won't find any examples of them used together. "EACH ELEMENT" is shown with parallelism, and the between symbol is shown with profile but none of them are shown together. By your logic, this would mean that the tip is wrong.
I don't feel like my last post was attacking you personally but if you took it that way then I apologize profusely. I was calling your definition of extension of principle asinine, not you. Also, your constant statement that we're just "making stuff up" really rubs me the wrong way for some reason. It is, however, my job to watch what I say so as not to insult people because nothing productive gets accomplished that way. So again, I'm sorry if you took personal offense.
Powerhound, GDTP S-0731
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Inventor 2013
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RE: Parallelism on per unit basis
For the "extension of principles" issue, CheckerHater, you are really hanging everything on that statement about using a note. OK, I get that, but isn't that a wee bit strong? Recall that GD&T is a language and every possibility cannot be shown in the standard. It's like a dictionary: You won't find the word "disqualification" in most print dictionaries, but you may find the words "qualification" and/or "disqualify." You claim that extension of principles is a "totally made-up concept," so you are telling me that we can never use the word disqualification because it isn't in the dictionary!
I would also add that the idea of extension of principles should be additive, but never subtractive. What I mean is that we can take a concept and extend it to apply in a situation that still retains the main purpose of that symbol or concept, though not specifically identified in the standard -- such as per-unit parallelism. But we can't take an established idea and rip it apart so that it is missing a constitutive element -- such as using position when the only control desired is perpendicularity (sorry to bring it up, Jim!). To me, that is not an extension of principles because it violates the standard's requirement that position at least control location.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
Powerhound, by using the words “making up” I did not imply someone lying, personally or as a group, so it wasn’t meant as an insult.
Belanger, from my examples, would you consider” tangent profile” or “tangent position” extension of principle or illegal? Just to get better understanding on where you stand.
RE: Parallelism on per unit basis
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Parallelism on per unit basis
http://www.eng-tips.com/viewthread.cfm?qid=314178
Do I have to dig deeper into history of your replies on this forum?
RE: Parallelism on per unit basis
RE: Parallelism on per unit basis
RE: Parallelism on per unit basis
RE: Parallelism on per unit basis
Four of you guys formed a mob to beat me up with extensions of your principles.
Had no choice but to throw a sucker-punch. Not like you haven’t been warned…
RE: Parallelism on per unit basis
Jim Sykes, P.Eng, GDTP-S
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