Dimensioning surfaces

[TrailMaker004]

We have a question of expression/interpretation. In the attached sketch, the primary datum is a contoured surface -this is not new for us as we have worked with this many times before. The contour is defined by the baic dimensions and the profile tolerance. The (2) .437 dia holes are located in X & Y by the .500 basic dimensions.

Our question is this: since the X position of the holes are dimensioned by the .500 basic(s) from the (2) opposite end surfaces, and the 5.000 length can vary as much as +/-.006 in actual length within its profile tolerance (+.003 per side = +.006 total, -.003 per side = -.006 total), will those holes be tied to those end surfaces with respect to their X position, and thus vary in X position consistent with the +/-.006 potential length variation of the profile? Or, as some suggest on this end, because the 5.000 is a basic dim, the hole locations are tied to the implied centerline of the 5.000 basic, and their X location will not be affected by any actual variance in the profile of A regardless of what surface they are dimensioned from.

The reason the holes are being dimensioned from the end surfaces is because there is a family of parts and dimensioning from the centerline vs as described above would require a large tabulation to cover all versions.
Thanks.

 

[dtmbiz]

Quote:
"I'm one of those weird guys that actually enjoy a lively debate because I think we can learn a lot that way."

.....me too!

I completely agree about the “lively debate” and now that I know; Who knows... maybe it was me venting..

In my quite lengthy experience as a design engineer I have seen many callouts that violate the basic fundamentals of the standard. It bugs me. I am a passionate literalist.... not a legalist...

I believe the standard can be deviated from, as long as there is an amendment to explain the deviation. Others that contribute will sometimes call these deviations… “an extension of principle” I do not have a problem with that, but do believe there must be a amendment to clarify the subject. GDT / ASME Y14.5m already gets a bad rap because so many say it is confusing. So I like to always start with the basics and go from there with more complex concepts. I will say that I do like to “stir the pot”. I believe it stimulates one another to “think”.

I have read in a number of threads, discussions that touch on the DRF concepts. IMO this is not drifting off course because of the direct impact on every callout referencing a DRF.

I do appreciate your point of view considering your background and present position. This is probably an area of my least experience. I could probably learn some things from you. Axym is another contibuter that I believe is in your field. I like to read his posts also. However, the bottom line for me is product development. Defining a model / drawing according to standards that convey design intent as clearly as possible.

As far as your question to me regarding parts that aren’t fully constrained… yes I accept them. In the case of a cylindrical part with coaxial diameters, it isn’t necessary at times to constrain the rotation, particularly if there aren’t any features requiring “clocking”.
As far as complex parts, lets say a turbine vane, I understand it may not be straight forward to identify a DRF, however, possible in my thinking. My view point is that you need an origin to make x, y, z measurements. I would use target points, areas, etc to define the DRF. The issue IMO is to have all parts setup in the same way to consistently inspect. Figs 4-42 and 4-54 in the 2009 std are cases in point.

I have been doing design for a long time, but always hope that I am still “teachable”. I have taught various CAD, drafting, design, and dimensioning classes within various companies. I found that I have always learned or realized something new myself. I like to learn.
You are right… I need to get to work myself… my current Mgr is fairly lenient with me regarding this site though. I often pass-on what I have learned from folks that contribute here.

Thank you for the time to introduce yourself Nobigdeal and my apologies to others for spending so much time on me and where I am coming from.

 

[dtmbiz]

Whoops..... attached my post scratch pad instead of markup
my appologies

 

[dtmbiz]

Bad day.... Datum C would be attached to the FCF "perp to A | B. The flat on the bottom.

 

[ptruitt]

Only assuming some functional requirements for this part, I propose the attached design.

 

[flash3780]

I popped into this discussion and admittedly glossed over some of the comments, but per the last sketch posted:

1. I think your profile callouts will require datum references... I've seen profile used without for flat sheet metal shapes, but I think you'll want datums on this one.

2. Why not use a +/- tolerance on the hole size with a position tolerance. This allows you to use an MMC modifier (which is usually a functional callout).

3. You've specified an all-around profile on the shape in the orientation view. You may consider a maximum radius callout for the sharp edges. (ASME Y14.5 mentions that)

4. Why use a profile on the upper and lower surfaces shown in your flip-out view? A +/- tolerance would suffice.

No need to make things more complicated than they are.