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

 

[Belanger]

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

 

[dingy2]

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.

http://www.qmsi.ca

 

[REDesigner09]

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

 

[Belanger]

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

 

[lifttrucks]

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.

 

[DeanD3W]

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

http://www.d3w-engineering.com

 

[REDesigner09]

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

 

[ptruitt]

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

 

[REDesigner09]

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.

 

[dingy2]

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.

http://www.qmsi.ca

 

[powerhound]

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

 

[axym]

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.

http://www.axymetrix.ca

 

[ewh]

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." - [small]Robert Hunter[/small]

 

[REDesigner09]

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.

 

[Belanger]

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

 

[powerhound]

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

 

[dtmbiz]

If blade stacking axis falls on centerplane of feature of size "Y" then....

Attached dwg is possible example....

 

[REDesigner09]

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

 

[REDesigner09]

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?