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Parallel Callout?

Parallel Callout?

Parallel Callout?

(OP)
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

RE: Parallel Callout?

There are several ways to go on this, but I would clarify what datum Y is.  Although a datum can theoretically be an axis, the drawing should have the datum symbol (triangle) attached to a physical feature.  (Currently we don't know how to derive datum Y in an actual physical measurement -- from the root or halfway up, etc.?)

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

RE: Parallel Callout?

One cannot have a centre line as a datum. It must be a feature such as an OD or ID to create this centre line.

Your parallelism feature control frame is not to the ASME Y1.45 standard (any edition). Where is the reference datum? It should be shown on right hand box in the feature control frame. What does .010Y mean?

Designers - I would not suggest using GD&T on drawings at all until the Designer has had extensive training and understanding of the subject. The understanding takes a long, long time. I know that it took me 10 years of training until I was comfortable in this subject.  

Dave D.
www.qmsi.ca

RE: Parallel Callout?

(OP)
Hi Belanger & Dingy2,

  Thanks for the feedback.

  To begin with, the ".010Y" is translation issue from being converted from the CAD application to '.pdf' format.  I was trying to define that the section cut (AK-AK) & projected view (F-F) are parallel to Datum Y.  As for the callout of F-F, perhaps, this was the past company's practice that I worked for, who claimed that they knew their GD & T.

  I did move the these section callouts by projecting or creating a top view, then plasing these section or view callouts.  This way, it's more visual that these callouts are parallel to the LE & TE root faces or to datum Y.  With these views, then I rotated CCW or CW 90 degrees, which I believe is more representative of how I got the views.

  The datum "Y" is suppose to represent my stacking axis of the rotor blade.  Why can't this represent the center?  There is suppose to be a centerline on top of it, which may be more representative of the center.  For the most part, I'm following what other (more experienced) turbine designers or engineers or OEM companies have done or have been doing.

  What are you suggestions to get View F-F & Section AK-AK in the orientations shown in  picture, as well as to represent that these views are parallel to my datum Y or center stacking axis?

  
Thanks
   

RE: Parallel Callout?

I'm not sure what to say about the views, but the reason you can't represent the center directly as a datum is because we can't touch a center.  Therefore, the datum feature symbol needs to indicate the physical item that would be grabbed/probed/touched in order to determine the center that you are trying to call the datum.  See any GD&T reference book and look at the chapter about datums.

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

RE: Parallel Callout?

REDesigner09,

To reiterate what Mr. Belanger said, 4.8.2 in the Y14.5-2009 standard states that "The datum feature symbol identifies physical features and shall not be applied to center lines, center planes, or axes." (4.3.2 in the 1994 Revision).

As a simple example, lets say you are making a drawing of a piece of mechanical tubing. You identify the center line as a datum feature. How is inspection going to know if you are identifying the axes of the ID or OD of the tube? The ID and OD will never be perfectly coaxial to one another - so it would be left to inspection to assume how to inspect the part.

 

RE: Parallel Callout?

This has been said in a couple of ways, but in one instance in this thread it was incorrectly stated that a center line cannot be a datum.  If a datum feature is identified which has an axis, such as a cylindrical or conical feature, then the axis of its datum feature simulator is the datum.  An axis can absolutely be a datum, but an axis cannot be a datum feature.  As said above, if a datum feature label is applied to a center line/axis/center plane, there there it is very likely that it will not be clear which feature is to be used to create the datum axis or datum center plane, so this practice is prohibited by Y14.5 (as is pointed out above by lifttrucks and Belanger).

It's important to keep the difference between a "datum feature" and a "datum" in mind.  A datum feature is a specially designated feature (a surface) on a part and a datum is a point, line (axis), plane (possibly a center plane), point on a line, line on a plane, or point on a line on a plane (if this list of potential datums seems too long, based upon past training or experience, then please see Y14.5-2009 Figure 4-3, page 50 and section 4.3 on page 48).

Dean
www.d3w-engineering.com
 

RE: Parallel Callout?

(OP)
Hi Everyone,

 Interesting feedback.  Unless I'm misinterpreting something here, using a datum at a center was a practice at a major Fortune 500 company that I used to work at.  Additionally, this company had a nationally ranked GD & T specialist.

  I'll have to go back to see "if" I can find some of my past drawings to see if I'm interpreting correctly.  Looks like I need to find a ASME book as well.

Thanks
 

RE: Parallel Callout?

Dean really nailed it when he said "...keep the difference between a "datum feature" and a "datum" in mind." The focus on this issue as evolved and your old drawings should be considered carefully. Even the experts would probably use different methods to detail that drawing now than they did when those drawings were created. In the aviation field, you will need a very deep understanding of these issues if safety is relying on your expertise. It is entirely possible that a lawyer will be asking you to explain what that funny symbol means. (I have been there, and I will probably be there again. Not fun.)

Peter Truitt
Minnesota

RE: Parallel Callout?

(OP)
Hi Everyone,

  I noticed that there's a reference up above to 2009 standards. It doesn't appear which standards the company I work for uses.  They are still using ASME Y14.5M-1994 standards.

  I'm not sure if this makes a difference or if standards have changed with the new version.  

  What I do know is that I've seen or been directed by companies worked for that they use a Datum at center of features.

RE: Parallel Callout?

4.6.7 of ASME Y14.5M-94 states that "Where a datum reference frame has been properly established but its planes are unclear, the datum feature symbol my be applied to appropriate extension or center line as needed." That is it on applying the datum feature symbol on a center line and the 2009 revision does not have this statement at all.

Having a center line with a datum symbol does not help anyone on the shop floor. Is it the OD or ID? As Dean stated, the center line is the datum but the datum features creating that center line must be tangible - OD, ID, thickness, etc.  

Dave D.
www.qmsi.ca

RE: Parallel Callout?

Para. 4.3.2 states "datum feature symbol...shall not be applied to center lines, planes, or axes"

It is an absolute no-no to do this. Fortune 500 company or not, the practice is expressly prohibited in the standard.

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Parallel Callout?

Dave,

I strongly agree with you and the others that the datum feature label should only be applied to a tangible feature and not to a center line.

The passage that you quoted is misleading, however, if the context is not mentioned.  Section 4.6.7 deals with datums established from complex or irregular surfaces using datum targets.  This a very different situation from the one being discussed - the "center lines" that the passage mentions are not the same thing as the centerline of a feature of size.  To be honest, 4.6.7 contains some unfortunate statements and really isn't one of Y14.5M-1994's brighter moments (IMHO).   

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Parallel Callout?

A simply work-around to paragraph 4.3.2 is to append the datum callout with "CL" or "AXIS".  Of course, this is predicated upon the existence of a datum feature to begin with.

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

RE: Parallel Callout?

(OP)
Hi Everyone,

  Here's a question.  When creating CAD models, we often use a datum plane as center, particularly if the component is symmetrical. This usage or reference to center often gets carried over to the drawings.

  I agree with the standard, but questioning why all these companies I've worked for small or big, has been using this practice.   

RE: Parallel Callout?

Probably because it was an environment where the design folks were immersed in the design world, and had minimal contact with the people that were actually manufacturing or inspecting the parts!  If they had been in regular contact with the mfg group, the word would have gotten back to the designers -- fast -- that having a datum be identified on a center line is ambiguous.

That being said, the ASME/ANSI standards have been very clear about the datum symbol's location, at least since I first learned GD&T (under the 1982 standard).   

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

RE: Parallel Callout?

So here's the tip that has been posted about this subject before. Be sure to watch the video as it is a little more enlightening than just reading it.

http://www.tec-ease.com/gdt-tips-view.php?q=130

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Parallel Callout?

(OP)
Hi Dtmbiz,

  Thanks you very much for the mark up.  Some of my GD & T - the Parallel Composite frames did not translate correctly when converting from CAD to a '.pdf'.

  I also fixed my rotation callouts by moving my 'F-F' & 'AK-AK' callouts to the top view.  Here, it's seen that the LE & TE root faces are parallel to my original Y, which is what I was attempting to define.

  My current view is slightly skewed from the projected or front view it came from, which is the reason I'm trying to define these LE & TE root surfaces

Thanks again for the mark up

RE: Parallel Callout?

(OP)
Hi Everyone,

  Attached, is a picture of a commonly used datum scheme used through out the aerospace & gas turbine industries I've worked.

  From these defined datums, various GD & T would be applied in the drawings, referencing one or more of these primary datums.

  What are your thoughts of this practice?

 

RE: Parallel Callout?

(OP)
Hi Everyone,

  Please provide your thoughts with the picture I attached above.

Thanks
 

RE: Parallel Callout?

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." - Robert Hunter
 

RE: Parallel Callout?

(OP)
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

RE: Parallel Callout?

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
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Parallel Callout?

(OP)
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?

 

RE: Parallel Callout?

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

RE: Parallel Callout?

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
www.d3w-engineering.com
 

RE: Parallel Callout?

(OP)
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?

RE: Parallel Callout?

(OP)
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


   

RE: Parallel Callout?

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

RE: Parallel Callout?

(OP)
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

RE: Parallel Callout?

(OP)
Hi Kenat,

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

 

RE: Parallel Callout?

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

RE: Parallel Callout?

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

RE: Parallel Callout?

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

RE: Parallel Callout?

(OP)
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.

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