Watch Where You Put That Triangle - Discusion 1

[psiwak]

I had discussion about what's mean datum target on extension line.
My opinion is that according to ASME Y14.5 1994 3.3.2 there is no difference where to put and which view (outline, extension line, align with dimension, top view, plain view) but my adversary claim that according to TEC-EASE GD&T Tips when I put on extension line than Datum is tangent to cylinder. Unfortunately English is not my native language, but I understand from description of second figure that this is accordance with Y14.5 but for clarity and to avoid doubts shouldn't be use. I know that Y14.5:1994 doesn't show example with datum target on cylindrical feature in side view but also 3.3.2 (and whole standard) no mention about tangent datum plane.

My questions are.
Datum A from Fig 2 produce datum axis?
Author of this tip wants to introduce good standard (from what I completely agree) of drawings and not allow to show datum target symbol which is not align with dimension on plain view of cylindrical feature

Regards
Pawel

 

[powerhound]

Right, and that's why they have the illustrations, so that we don't make that mistake.

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[pmarc]

powerhound,
I guess we do not want to start a discussion about implications of paragraph 1.1.4 to what is or is not shown in the standard, do we?

J-P,
I like the first sentence of your reply, but do not really understand the other considerations. It sounds to me like splitting hairs. This is what first part of 3.3.2(c) in Y14.5M-1994 exactly says:
"placed on the outline of a cylindrical feature surface or an extension line of the feature outline, separated from the size dimension, when the datum is the axis."

Doesn't the bold part exactly describe the situation shown in fig. 2?

 

[powerhound]

No, you're right pmarc. We don't want to get into that discussion, but the extension line in the OP is on the outline of a rectangle.

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[pmarc]

A rectangle which is a cylinder as a matter of fact (because the diameter symbol is there).
Out of curiosity, how else would you imagine an extentsion line of the outline of cylindrical feature? Could you explain or offer a sketch?

 

[Belanger]

And following that thought -- the rectangle is indeed a "cylindrical feature"! That's what I meant, pmarc.

But we can infer from Fig. 3-4(d) and (f) of 1994 that paragraph 3.3.2(c) was referring to a cylindrical feature only in the view where it appears as a circle.

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

http://www.gdtseminars.com

 

[powerhound]

I don't have to imagine the extension line on the outline of a cylindrical feature or even offer a sketch, it's shown in Fig 3-4(d & f).

...and I am in agreement with what JP said. I wasn't challenging that the rectangular shape wasn't a cylinder, I was trying to say that the extension line is not extended from a circular shape.

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[MechNorth]

Ok, playing Devil's Advocate (people actually pay me to do that!), from basic print reading, we know that an extension line from a drawing feature line is indicating the surface. For a cylindrical feature shown in side-view, the extension line from the lower feature line is thus indicating a surface; the surface, as defined by a diameter symbol or another view, is a single continuous surface of a cylinder. It's the same logic & print reading that tells us that for a rectangular prism, an extension line from the lower feature line in the side view represents the bottom surface.

3.3.2 (c) ('94) does not specify an end-view of a cylindrical feature, just the "outline" of a cylindrical feature surface ... the side view is a valid outline as far as I can tell.

There are a lot of training materials, publications and tips from various experts that I don't agree with the wording of. Sometimes we write things that make perfect sense, and are technically correct, but are open to selective- and mistaken-interpretation.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[pmarc]

powerhound,
If Figs. 3-4(d & f) show the datum feature symbol placed on the extension line of the outline of a cylindrical feature, then we must have different understanding of what extension line of the ouline is. These two figures show nothing but a datum feature symbols placed on the extension of dimension line. And that is the difference.

Let me try the other way. Read 3.3.2(a) and then read 3.3.2(c) again. They both use wording: "on an extension line of the feature outline". Now look at datum feature symbol B placement in Fig. 3-3. This is what 3.3.2(a) means by saying: "placed on an extension line of the feature outline", correct?. By analogy, this is my understanding of what "placed on an extension line of the feature outline" in 3.3.2(c) means. Lack of pictorial explanation for sure does not help in the discussion, but it is not the reason to claim that such practice is invalid.

 

[powerhound]

Nothing in figure 3-3 indicates that either feature is a diameter so let's not use that at all other than to illustrate the difference between a datum feature on a surface and on an extension line. We both know that difference.

My contention is that an extension line as shown in the OP indicates a line and a line only. I've gone through this with you before. Previously, you insisted that if something was not directly supported in the standard, such as parallelism on a unit basis, then it was not valid. Extensions of principle were simply "making stuff up." Now that you have no direct support for something you believe in, you cite 1.1.4.

You clearly know GD&T very well as evidenced by the multitudes of other helpful posts I've read on here by you, but you don't seem to be open to entertaining the notion that maybe you're not thinking about something right. I guess the fact that not a single other poster on this thread, or on the other one, sees it your way doesn't matter a bit to you.. Jim has stopped trying and has resorted to playing Devil's Advocate.

As I said before, I respect and believe in your knowledge of GD&T so I'm not slamming you at all. There is even disagreement among the experts and this is where I'm just going to let it go.

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[pmarc]

You are free to think anything about me. You can think that I am not open to entertaining the notion that maybe I am not thinking about something right - it is you right and choice. You can take advantage of this parallelism-per-unit thing in every future discussion in which we will be having any kind of disagreement. I don't care as long as the discussions will be based on logical and substantial arguments and not some sort of emotional cogitations.

During the whole thread I have not read a single argument clearly proving that I am incorrect in my thinking. Instead of it there is a whole bunch of "one might think", "may be interpreted", "might be misinterpreted" stuff, plus you stick to two figures 3.4(d & f) that have nothing to do with what I am really talking about. The recent discussion heading into direction that 3.3.2(c) applies only to views where a cylinder is shown as a circle also does not have any support in the standard, as it was explained by Jim the Devil's Advocate.

That being said, if you still want me to be convinced to your standpoint, you or somebody else will have to prove that fig. 2 in original post is really not what is hidden behind wording: "datum feature symbol placed on an extension line of the feature outline, separated from the size dimension".

 

[Belanger]

Jim -- I guess I agree with you in principle. But if that's true (that "the extension line from the lower feature line is thus indicating a surface; the surface, as defined by a diameter symbol or another view, is a single continuous surface of a cylinder"), then there would be no need for the Tec-Ease tip because everyone should agree that the true datum is the axis [per 3.3.2(c)], even for the left-hand view in the OP's Fig 2.

So I guess the main point is: no matter what the standard says about a definition, make sure the drawing is clear!

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

http://www.gdtseminars.com

 

[MechNorth]

J-P, the tip still makes sense as it defines an appropriate (i.e. clear) way to communicate an intended tangent plane, and communicates an incorrect or inappropriate way that some people have been using (I was originally taught essentially that interpretation by a previous instructor who couldn't defend the interpretation with the standard ... or anything using the standard, actually). But certainly you are correct ... make sure the drawing is clear.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[psiwak]

To add fuel to fire
It seems to that the 2009 issue solve this problem in fig 4-45, isn't it ?

 

[Belanger]

You may have a point there, Psiwak, because the datum symbol for A doesn't conform to any of the options given in paragraph 3.3.2!

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

http://www.gdtseminars.com

 

[CheckerHater]

Looks like option (a) “when the datum feature is the surface itself” to me.

 

[Belanger]

You're right, CH. I was mis-reading it. Scratch my last post!

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

http://www.gdtseminars.com