Y14.5-2018 Published 1

[pmarc]

This is just to let you know that new version of Y14.5 is available.

https://www.asme.org/products/codes-standards/y145-2018-dimensioning-and-tolerancing

 

[axym]

greenimi,

The new stabilization default for RMB datum features will have some impact, but I'm not sure how much. I suppose that this depends on how often candidate datums on a rocking primary datum feature actually come into play. How often do you see a part rocked to an optimal orientation on a surface plate during inspection? I haven't seen that very much. When a part is CMM inspected, the software rarely/never tries different candidate primary datum planes.

Regarding total runout on a cone, I'm wondering what your objection is and why you feel it should be disallowed. Personally, I don't have a problem with it. Regarding the addition of the term "cylindricity", I don't think that this changes anything about the definition itself. It's a description, intended to aid understanding. When applied to a cylindrical feature, total runout limits the worst-case cylindricity error. It's an indirect consequence of conforming to the total runout requirement.

pylfrm,

Some of the additional pages represent new content, but a lot of it is from additional model-based versions of the figures. I also noticed that some of the figures are larger, taking up an entire page.

3DDave,

Total runout doesn't limit variation parallel or perpendicular to an axis. It's often portrayed that way, as this provides a useful description for cylindrical and planar surfaces. Point the indicator perpendicular to the datum axis for cylinders, and parallel to the axis for planes. But the requirement is really that the indicator needs to point normal to the basic surface. So this doesn't rule out cones and curved surfaces of revolution, but it does require that they be defined with basic dimensions and not with directly toleranced dimensions. This has been a sticking point - what to do when the angle of a cone is defined using a directly toleranced angle?

Dynamic profile cannot be covered by composite profile tolerancing - it's something different. Composite profile allows the tolerance zones in the lower segment to translate relative to the DRF. Dynamic profile allows the tolerance zones to "progress" (offset). I agree with pylfrm that this is a generalization of total runout.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[3DDave]

Evan,

That interpretation of total runout was never supported in previous versions; in fact, the application examples seem to go far out of their way to demonstrate only parallel and perpendicular applications. To say it's often portrayed that was is an understatement - that's the only way the standard portrays it.

There is no means from the stated rules to determine, for a real part, what it means in the absence of anything but a basic profile, what such a measurement might accomplish.

What really perplexes me is seeing no example of what actual driving need was put forward - what industry has long been crippled without this new feature? It seems very much like a language feature that has no engineering need, but would drive a company to have to use a CMM to determine compliance but without similar FEA support, for example, to determine variation affect on function.

On the plus side, there's now new training required and a new compliance check-box for CMM software to make sales differentiation points for sales and marketing; there's no way this is possible for any manual evaluation for the general case, even with dedicated fixturing.

Lest I be cast as a Luddite on this, I had need for essentially including a matrix multiplication into a specification because the desired relationship between two features was not orthogonal and the CMM software was too weak to make the calculation on its own. But I could point to the very real hardware and very real tolerance contribution to justify it.

 

[axym]

Dave,

The standard hasn't included examples of total runout on a cone or curved surface (well, at least in the later versions - Y14.5-1966 did have this). Y14.5-2009 makes the following statement on page 180:

"When verifying total runout, the indicator is fixed in orientation normal to and translates along the toleranced surface"

One of the total runout figures (9-3) also mentions "the indicator placed at every location along the surface in a position normal to the true geometric shape without reset of the indicator". Even though the feature in the figure is a cylinder, it isn't a big leap to apply the indicator description to non-parallel and non-perpendicular features.

One of the uses that I see for dynamic profile is to act as a universal form control. When applied without any datum feature references, it controls only form and nothing else.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[Sem_D220]

Can anyone tell what is the change introduced to the concept of a feature of size?

 

[greenimi]

The new stabilization default for RMB datum features will have some impact, but I'm not sure how much. I suppose that this depends on how often candidate datums on a rocking primary datum feature actually come into play. How often do you see a part rocked to an optimal orientation on a surface plate during inspection? I haven't seen that very much. When a part is CMM inspected, the software rarely/never tries different candidate primary datum planes.

I've seen (and actually pretty often) in our inspection department. If some holes in a plate are qualified for their perpendicularity to datum plane (and also their mutual relationship) with a functional gage, the inspector is allowed to wiggle the part / rock the part on the gage until he/she is able to fit all the gage pins thru the part into the gage plate. That is how our instructions are reading and are to be understood. But that is again 1994 standard.

Just thinking out loud (and fast forward to 2018 standard) how the inspector is using the same gage when the "single solution that minimizes the separation" is in effect by default. How he/she knows when that single solution is acheieved? Are you no longer allowed to wiggle the part on the gage?

Again, I am not saying that changing the default procedure is not a good move, but I am questioning the implication in the real life/ gaging inspection and even/or simultaneous requirements.

 

[axym]

greenimi,

With the new default of a single solution that minimizes the separation between the feature and the true geometric counterpart, the inspector is no longer allowed to wiggle the part on the gage. How the inspector knows that the proper single solution has been achieved is another question entirely. There are definitely some practical implications (unintended consequences?) associated with the new default - these are going to be discussed and debated for the next few years, I'm sure.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[3DDave]

Evan,

The new default should have been discussed and debated for the previous few years. There should not be any unintended consequences at this point. All implementation questions should have been investigated and solutions included as part of the document that demands them.

 

[greenimi]

Since I don’t like this discussion to die down, I would like to ask what do you think about negative virtual condition which looks like is allowed by the 2018 standard? Some will, probably, say that was allowed even in 2009, but not clearly spell out (or, at least, not to my knowledge)

Or what about, the chart where total runout tolerance has effect on the location of entire surface? Do you think that is correct? I am talking about the wording/verbiage in red.

 

[greenimi]

And one more: what about changing the terminology from "multiple datum feature-primary" to "common datum feature-primary"?
Maybe in the next ASME standard revision we will see "combined datum feature-primary" to align with ISO trend.

 

[mkcski]

I preordered a copy of the 2018 revision. It was supposed to ship on the February 21st. I has not shown up as of this morning. Is anyone else waiting too?

Certified Sr. GD&T Professional

 

[axym]

greenimi,

There is a new statement about negative virtual condition, but it isn't in the Tolerances of Position section. It's in 5.9.4.1 Explanation of the Surface Method:

"NOTE: When a geometric tolerance applied at MMC results in a negative VC (i.e. when a 2.0-2.5 internal feature of size has a position tolerance of 3.0, the VC is -1.0), the surface interpretation does not apply."

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[axym]

greenimi,

Regarding the statement that total runout controls the location of the entire surface, the correctness of this depends on your idea of what "location" is. Y14.5 doesn't explicitly define what is meant by location, but I would say that the statement is consistent with Y14.5's other descriptions of location. In the context of total runout applied to a cylindrical surface, location relates to coaxiality - the centering of the feature relative to the datum axis. The location of the surface does not relate to the radial distance of the surface from the datum axis.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[3DDave]

Total runout is a measure of uniformity of displacement relative to rotation about an axis; coaxiality control is a side effect. It is the axis-based version of parallelism vs a planar datum.

 

[greenimi]

Since I do not want this discussion to die (and I am trying to save it AGAIN ), I would like to ask another question / another one of my pet-peeve:

Why do you think that committee decided in 2018 edition to “adjust” the definition of the circularity with the unrelated actual mating envelope statement.

Fig 8-10 / 2018 states that each circular element of the surface in a plane perpendicular to the axis of the UAME shall be within……….
The equivalent figure in 2019 2009 states that each circular element of the surface in a plane perpendicular to an axis must lie between …………….

As we talked earlier, there some opinions that the newly addition (UAME) is a mistake.

Is it truly a mistake or an oversight? Or maybe intentionally those words have been chosen specific for cylindrical and conical surfaces .

What do you think?

Edit: I wrote 2019 instead of 2009 which I've been intended.

 

[mkcski]

It appears some of you have received your copies of 2018. Maybe you purchased the download PDF. I am still waiting for my hard copy. Did anyone else get their hard copies?

Certified Sr. GD&T Professional

 

[3DDave]

About the only thing that comes to mind is that UAME is computable by CMM and is discoverable by no other method. I don't know if this is just to be helpful or to plug a perceived hole, but it doesn't seem to me to be any more necessary than it is to require flatness of a width to be in relation to the UAME. Since UAME leads near the word "size" that would exclude cones, so there's that.

 

[axym]

greenimi,

Interesting observation about the circularity description and the new reference to planes perpendicular to the axis of the UAME. It's hard to say what they were thinking with that, because there are conflicting indications:
-As 3DDave pointed out, this would exclude cones because they don't have a defined UAME (despite this, Fig. 8-10 includes an example with a cone)
-The circularity section in the text (8.4.3) does not mention the axis of the UAME. It refers to planes described in 3.6 (a) and 3.6 (b)
-3.6 (a) describes planes perpendicular to the axis or spine (curved line)

I would have to say that the cutting planes do not have to be perpendicular to the axis of the UAME, despite what it says in the Fig. 8-10 caption.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[gabimo]

I would like to ask a question for the members of this forum who have or seen the ASME Y14.5-2018 release:

If in fig 10-52, the PLTZF is removed from the callout and a datum feature symbol is attached to the reminder of the FCF, would that be a valid callout?

Otherwise stated, could a primary datum feature be created from two different sizes cylindrical feature of size without resorting to use the multiple datum primary option (the option with dash connector such as A-B)?