Parallel Callout?

[REDesigner09]

Hi,

I have an projected right-side view & need to define the root form of a turbine blade.

In the projected view, there is a vertical datum that I'm calling Y. If looking at the top view, I have 2 planner surfaces (LE & TE sides) that are parallel with my datum Y plane. However, the root form itself is rotated at 15 degrees

I would like to know if my callout & rotation notes comply with ASME drawing standards.



I included a picture.

Thanks

 

[REDesigner09]

Hi Everyone,

Please provide your thoughts with the picture I attached above.

Thanks

 

[ewh]

Fortunately, my experience regarding vanes in the aerospace industry tended to follow the standard more closely.
If interpretation IAW Y14.5 is stated on the drawing, I would have a problem creating such drawings as shown in your example. If a different (company) standard was specified, I would find it much more acceptable (provided the dwgs actually followed that standard).
How can such datum structures be justified under Y14.5?

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[REDesigner09]

Hi Ewh,

That's what I'm trying to figure out to. One of the companies I worked at has high level nationally renowned GD & T "Expert". Additionally, with other major aerospace & gas turbine companies, this datum scheme is a common practice.

I assumed this was all in line with ASME standards as well. I'm not familiar with IAW Y14.5 though.

Anyone else have any insight to aerospace or gas turbine datum scheme conventions

Thanks

 

[powerhound]

I don't suppose you'd care to drop the name of this nationally renowned "expert" would you?

It is not surprising to me when companies widely adopt an errant practice. I've seen it frequently. It's really bad when these practices become part of a documented procedure. Then they'll never get fixed because nobody wants to acknowledge that they signed off of a bad process.

The bottom line is that those datum axes in your drawing have to be derived from an actual feature or features. Nothing indicates from which feature/s to derive them.



Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
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[REDesigner09]

Hi Powerhound & Others,

No, I wouldn't do that to the person or the Fortune 500 company he works for. As mentioned, I've seen this practice for as long as I have been working in the turbine industries - aerospace, gas, & other turbine industries.

Each has this similar practice & up until recently, I thought this was an industry acceptable practice. I'm assuming there's justification to this practice - right or wrong as it may be.

It's one thing if legacy (CAD) models & drawings had this practice, but I'm pretty sure that this datum practice is not going away anytime soon.

Is there anyone from the aerospace or other turbine compressor industries who can justify this?

 

[ptruitt]

When the geometry gets really bizarre, I think of ASME Y14.5-2009 and employing profile tolerancing, exclusively, without any datums. (I have never done this, but I would seriously consider it if I had to.)

Peter Truitt
Minnesota

 

[KENAT]

"IAW Y14.5"

"In Accordance With ASME Y14.5_-yyyy"

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[DeanD3W]

REDesigner09,
Powerhound said it well in his 2nd and 3rd sentences of his post on 23 March.

The figure you posted on 22 Mar does not follow any version of Y14.5, or any version of any standard I've ever seen.

The mark-up that was posted on 22 March does identify datum feature Y in a proper way, but looking at the part, I don't think datum feature Y orients the part relative to the mating assembly, so that means datum feature Y is not a good choice as a primary datum feature. Also in the mark-up, I don't know what datum feature W is or which degrees of freedom is supposed to constrain (the leader does not point to a surface or to a cylindrical feature of size, so the labeling is not per Y14.5) Datum feature Z might make sense, but without W's identity or role being clear, it's hard to say.

BTW - While Y14.5 allows datum feature letters X, Y or Z, and quite a few people use these letters, I would not use them... Especially now that coordinate axes X, Y, and Z can be used to represent a datum reference frame (see ASME Y14.5-2009 figures 4-43 through 4-46) having datum feature letters the same WILL cause confusion.

I think the drawing you're posting needs a meeting with design, manufacturing, inspection, and also a good "GD&T person" included. The part's constraint wrt to the mating assembly will drive datum feature selection and Y14.5 compliant labeling of those datum features is needed.

Dean

http://www.d3w-engineering.com

 

[REDesigner09]

Hi Everyone,

Thanks again for the great feedback. In dtmbiz's marked up example, Datum Y is moved to the TE root face.

During the CAD model creation, which seems to be a typical industry practice, there is a CAD feature called Datum Y. If no longer using this for the drawing side, what should this be called then?

On another drawing, I saw that there was defined distance from the datum face to the center stacking axis, which was then use as a primary positional reference. Does this comply with ASME standards?

 

[REDesigner09]

Hi Everyone,

This is a follow up question, trying to differentiate the usage of a Datum Feature created within a CAD application, such as ProE, NX or any other CAD application & the ASME Y14.5 Datum.

While creating a CAD model, Designers will often create 3 primary CAD datums that often establishes center areas of features.

Some time a go, Dtmiz was kind of mark to mark up my drawing example.

Back then, I showed a machine part. My question now is how do comply with ASME Y14. standards to establish Primary, Secondary & Tertiary Datums on a Casting part, that will be carried over onto the machine part?

As you will see in the picture example, I originally had my GD & T Datum at center of this turbine blade. Dtmiz suggested to move this callout to trail edge root side, which I kind of agree.

At least during the Casting stages, this area is not critical because it will be machined down or material removed. Therefor, I do not believe I can use this surface. Additionally, if looking from the top-downward, the root has a parallelogram shape.

As you will see in the picture, which is incorrect, I have 2 datums shown. There's suppose to be a horizontal datum, which is currently placed at center at the 3rd root serration. This can be moved to the top or bottom of the pin (not shown). My 'Y' Datum is suppose to represent the center of the airfoil or blade. These CAD datums, plus my 'X' datum not shown are critical datums used to position a lot of the blade features. However, it appears that I cannot use these because I would be violating ASME Datum usage.

What is the appropriate ASME Primary, Secondary & Tertiary Datums placement areas for Casting to Machine that will comply?

Thanks

 

[fsincox]

REDesigner09,
I work with the same type of geometry you do, impellers and blades. We also use a stack point/line for blade "profile" definition. The explanation above on datums vs datum features is really the key here. What is really being discussed above is how do we actually establish those planes on a real part.
What you show in the model picture is a part and some reference planes in a cad system. If you actually pick up one of these parts all, or at least most, of those planes are not physically there. We must tell the inspector how to "establish" them, that is our job as a designer when using GD&T. The fact that we then use them is OK and that is what you have seen. The fact we do not tell them "how to get there" is wrong, as stated above, if it has not been done on the past drawings you have seen.
This is not uncommon at all, many drawings did not tell the "whole story" in the past that is what GD&T was developed to do better.
Unfortunately GD&T is still sometimes not used at all and is very greatly misused and abused. While I belive most parts do benifit from it's use, these parts need it the most, however since they are not "shown in the standard" people tend to shy away from them.
Frank

 

[REDesigner09]

Hi Frank,

Thanks for the feedback. The above practice has been seen or used by some major Fortune 500 & approved by their GD & T gurus, which is probably half the reason I'm confused on this topic area.

However, there instances that I've seen more formal GD & T practices, as well.

Throughout the CAD Modeling processes, there are typically 3 CAD datums used to establish the primary position & orientation of the part. In some instances, like mine, we also try to establish or mimic a Casting -to- Machine process through the CAD models & drawings.

How do I establish a Datum on a hard face between Casting & Machining, such as the Root Side surfaces, if it is suppose to be one of my primary datum surfaces?

See reference picture already submitted above.

Thanks

 

[KENAT]

Would datum targets be of any assistance?

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[REDesigner09]

Hi Kenat,

We are using Datum Targets to establish the 6-point nest. Do you have something else in mind to use these?

 

[fsincox]

REDesigner09,
I believe it might have been done with gage pins based on your drawing. One of your views shows (2) circles represented (AK-AK, I think). Simulated datum features are often used to simulate how the part will fit in the assembly. Understanding the function and what it needs to do is the key. I suspect the part locates somehow using that “nest” which is also where the pins are shown. I might then use them to establish (2) of my planes the third might be created off of the face F-F is dimensioned from, particularly if it represents a functional installation surface.
I am assuming here that the tapered toothed feature is the “nest” and it will be used to mount into a hub somehow?
This would then give you actual physical features to establish your planes from.
Frank

 

[fsincox]

Also whose drawings are you looking at? The ISO, up untill it's last revision, allowed datums shown on centerlines. Currently I believe it is not now a "recomended" practice for the same reasons mentioned here.
Frank

 

[fsincox]

P.S.
I work for a major Fortune 500 company, maybe we work togeather and don't know it.
Ken,
I have no problem with targets.
Frank

 

[REDesigner09]

Hi fsincox & Others,

There will be .094 pins in the 3rd serrations of the root, but only at the machine stages. Ideally, this is where I would like to establish my GD & T datum Z (horizontal datum) by placing the datum at the bottom or top of the pin surface. Still now sure how this is accurately measurable but it was suggested by someone. At casting level the root is not defined enough to insert .094 pins & pretty much all root surfaces are "as cast" features. Someone suggested using the airfoil & 6 pt. nest to establish the Primary, Secondary & Tertiary datums. What are your thoughts & on this?


As for the Fortune 500 company - There's probably about 5 major turbine international companies. I'm sure we've worked for one of them at some point of time & perhaps a few of them during our careers.