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Watch Where You Put That Triangle - Discusion

Watch Where You Put That Triangle - Discusion

Watch Where You Put That Triangle - Discusion

(OP)
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

RE: Watch Where You Put That Triangle - Discusion

Fig 2 does not produce a datum axis. The only way to produce a datum axis from a cylinder is to do it according to the figures in the first set of examples in the tip. If you attach the triangle offset from the dimension line then the meaning is ambiguous according to the ASME standard but could be interpreted as a tangent line to the cylinder arc. If that is your intent, then use a datum target line to remove any ambiguity. If your intent is to indicate the cylinder axis, then do it as shown in the first examples.

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

RE: Watch Where You Put That Triangle - Discusion

I agree with PowerHound, and I don't necessarily agree with the Tec-Ease tip. The standard tells us clearly how to indicate a datum to be an axis, and how to designate a datum derived from a surface. But the one shown with the datum symbol on the bottom of a cylinder -- not associated with a feature of size -- is ambiguous, in my opinion. It doesn't fit any of the prescribed methods to identify a datum feature.

Paragraph 3.3.2 tells us that we can place the datum feature identification symbol on an extension line "when the datum feature is the surface itself." But a single tangent line at the bottom of that cylinder is not "the surface itself." A datum target symbol could be used, but I don't see the standard indicating that a regular datum symbol on that tangent line equates with a target line.

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

RE: Watch Where You Put That Triangle - Discusion

Well, 3.3.2(c) of Y14.5M-1994 clearly says that if datum feature symbol is placed on a extension line of a cylindrical feature separated from size dimension, the datum is considered to be an axis. In the light of that Tec-Ease tip is not in accordance with the letter of the standard.

RE: Watch Where You Put That Triangle - Discusion

One might think that Para.3.3.2(c) of 2009 would make things more clear, but unfortunately it only references illustrations where “cylinder outline” is a circle.
Considering that Tec-Ease tip clearly suggests showing target line (adding second view?) to avoid ambiguity, I don’t see it being in direct violation of the standard.

RE: Watch Where You Put That Triangle - Discusion

The tip says: "In the view below, the datum may be interpreted as a line lying in a plane tangent to the feature indicated."
For me this is in direct violation of the standard. If one knows what 3.3.2(c) says about interpretation of such placement of datum feature symbol, the datum may not be interpreted as Tec-Ease suggests.

However I agree that the only way to indicate that tangent plane (or tangent line as a matter of fact) is a datum is to use datum target line.

RE: Watch Where You Put That Triangle - Discusion

(OP)
The problem started when I interpret the old drawings (about 20 years and more) where datum symbol is attached to cylindrical surface to extension line or to outline in plain view (similar case to Fig2)
According to 3.3.2 (c) I interpret it as a Datum Axis not as a tanged plane because in many cases Rounout, Cylindricity is measure with ref to this Datum.
Can I refer with interpretation in FIG2 to 3.3.2 (C)? If not the reason is the lack of proper drawing in Y14.5:1994?

RE: Watch Where You Put That Triangle - Discusion

If the drawings are indeed more than 20 years old, I would search for the answer in ANSI Y14.5M-1982 not in '94 edition.
I do not have '82 version with me, but if there is no difference in interpretation of this particular problem between '82 & '94, I would say the drawings are correct and the datum is axis (especially if it is referenced in runout tolerances).

P.S.: Cylindricity tolerance cannot use any datum(s) as reference.

RE: Watch Where You Put That Triangle - Discusion

I think when Don said it "may be interpreted", the context was "might be interpreted." not "is allowed to be interpreted."

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

RE: Watch Where You Put That Triangle - Discusion

Then he adds “If line contact is desired a datum target line should be indicated”.
So, if you actually show datum target (say, in second view) your intent will be clear.

RE: Watch Where You Put That Triangle - Discusion

powerhound,
Each print, even the perfect one, is a potential subject of different interpretations. It is the role of GD&T standard invoked on the print to reduce these multiple options into a single one.

I agree, this way of datum feature symbol location is not the most common option, and not the one I would use if wanted to define datum axis, but Y14.5 clearly says how it should be interpreted. I will not even try to guess what Don meant in his tip - I only see interpretation that is against official Y14.5 GD&T law and adds confusion (if we look at OP's question).

RE: Watch Where You Put That Triangle - Discusion

Okay, let me amend my original supposition. Maybe what Don meant was that it "might be misinterpreted..."

Don't get me wrong, I vehemently disagree with this way if the intent was to indicate the axis of the cylinder as the datum. It's way too easy to do it the right way and eliminate ambiguity. Either use a datum target line OR move the triangle to the OD of the cylinder or in line with the dimension line. As it is, the drawing is incomplete and has no correct interpretation.

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

RE: Watch Where You Put That Triangle - Discusion

And I keep saying that the drawing shown in left upper corner of fig. 2 from initial post is complete if we are talking about datum feature identification per Y14.5M-1994 and has got one and the only correct interpretation.
Why do you think it is incomplete and ambiguous? Because the method used is not as common as the other methods shown in the tip?

RE: Watch Where You Put That Triangle - Discusion

Maybe you should point me to where the interpretation of Fig. 2 in the OP is clearly stated in the standard. I can't find it.

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

RE: Watch Where You Put That Triangle - Discusion

The left-hand picture in the OP's "Fig 2" does not comply with the ASME standard (I guess we are sticking to 1994 for now). The closest thing that it comes to is paragraph 3.3.2(a), but that is allowed if "the datum feature is the surface itself."

However, that doesn't really apply here, because we are left hanging with this question: if the "surface" is the datum feature, what is the real datum? One could argue it's the axis, since this surface wraps all around into a cylinder; or you could argue that it's a plane, since some folks might think you're just identifying a tangent line, not the actual surface. See the confusion?

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

RE: Watch Where You Put That Triangle - Discusion

PowerHound nailed it when he said "may be misinterpreted as". My first GD&T instructor gave me the tangent plane explanation, which gave me heartburn because you can't specify where on the perimeter the tangent plane acts. Don Day (Tec-Ease) was the one who corrected that particular error in interpretation. If you want a tangent plane, use a datum target line.

The perceived ambiguity comes from the reality that many people won't recognize that section 3.3.2 (c) exists and gives explicit instructions on interpretation.

Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com

RE: Watch Where You Put That Triangle - Discusion

powerhound,
Doesn't 3.3.2(c) in '94 and '09 editions of Y14.5 describe what is shown on the left-hand picture in fig. 2?

Jim,
Many people do not recognize that a lot of different rules exist within Y14.5 realm. Take simultaneous requirement concept just as one example. Does it mean I should put SIM REQT note under each positional/profile callout referencing to the same DRF because otherwise the simultaneous requirement may not be recognized at all? If I wanted to follow "may be misinterpreted as" logic of the tip, this is exactly what I should do in order to avoid misinterpretations, despite the fact that certain rules have been already implied by invoking Y14.5 on the print.

But coming back to the original issue, I miss one clear statement from you, therefore could you answer to following question: "Knowing that Y14.5 is in charge, what is the datum in fig. 2 and is it clearly defined by the standard?"

RE: Watch Where You Put That Triangle - Discusion

pmarc,

No it doesn't. At the end it gives the figures which to refer to for an illustration of the description (3-4(d) and (f)). Neither of them show what is in Fig 2 of the OP. The extension line is not of the feature outline.

Regarding your last sentence. I'm pretty sure it was intended for Jim but I'll chime in. There is no valid datum in the OP. One could assume but whatever the assumption, it is unsupported by either standard.

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

RE: Watch Where You Put That Triangle - Discusion

The funny thing is -- if you ignore the pictures and simply read 3.3.2(c), it could actually go with the Fig 2 given in the OP. Two problems, though: if we try to apply 3.3.2(c) to Fig. 2 above, then the datum is the axis, not a tangent line. Secondly, the standard really meant to say, "if the datum feature symbol is placed on the outline where the feature appears as a cylinder..."
That's different than saying "placed on the outline of a cylindrical feature." A picture of a rectangle could be a cylindrical feature!

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

RE: Watch Where You Put That Triangle - Discusion

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

RE: Watch Where You Put That Triangle - Discusion

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?

RE: Watch Where You Put That Triangle - Discusion

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

RE: Watch Where You Put That Triangle - Discusion

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?

RE: Watch Where You Put That Triangle - Discusion

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

RE: Watch Where You Put That Triangle - Discusion

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

RE: Watch Where You Put That Triangle - Discusion

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 www.profileservices.ca
TecEase, Inc. www.tec-ease.com

RE: Watch Where You Put That Triangle - Discusion

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.

RE: Watch Where You Put That Triangle - Discusion

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

RE: Watch Where You Put That Triangle - Discusion

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".

RE: Watch Where You Put That Triangle - Discusion

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

RE: Watch Where You Put That Triangle - Discusion

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 www.profileservices.ca
TecEase, Inc. www.tec-ease.com

RE: Watch Where You Put That Triangle - Discusion

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

RE: Watch Where You Put That Triangle - Discusion

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

RE: Watch Where You Put That Triangle - Discusion

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

RE: Watch Where You Put That Triangle - Discusion

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

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