Parallelism on per unit basis

[powerhound]

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,

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2010
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
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[CheckerHater]

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.

 

[powerhound]

CH,

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
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[Belanger]

I too don't get what the problem is with defining tangent plane. ASME Y14.5 is clear on that, and so is just about everybody here.

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

 

[CheckerHater]

OK. It looks like some of my points are actually getting thru.

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.

 

[Belanger]

the tangent plane modifier can certainly be used on profile of a surface. Not on position, because there is nothing planar about position.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[Belanger]

(Position can be applied to a center plane, but that is already defined as being derived from the actual mating envelope, which is a tangent plane idea.)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[pmarc]

CH,

http://www.eng-tips.com/viewthread.cfm?qid=314178

Do I have to dig deeper into history of your replies on this forum?

 

[CheckerHater]

Dig until you find parallelism per unit.

 

[CheckerHater]

I also use words like "industry standard" when it suits me and call myself "checker" in my resume.

 

[pmarc]

 

[CheckerHater]

Will it make you feel better if I say I am not very proud to give you undue exposure?
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…
:-(

 

[MechNorth]

JP - I'll let it slide ... THIS TIME!!!

Jim Sykes, P.Eng, GDTP-S
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