Best way to construct compound datum axis

[cbrf23]

I'm posting here because I wanted some input on the use of a compound datum in this scenario as I couldn't find any examples showing this setup in Y14.5-2009

I've been working with our casting supplier to establish an inspection method for checking position of some ID features to their OD counterparts.
We've created a CMM setup which we are happy with and now I'm just trying to ensure this setup is appropriately defined on the print.

The DRF is created as follows:
Primary datum (plane): Measure a plane off the face identified as datum A.
Secondary datum (axis): We use a v-block on each of the features identified as datums B and C and we push the V-blocks up against a physical stop on the CMM table and measure the axis off this stop.
Tertiary datum (point): Measure a circle off the feature identified as datum D

In the image attached I've tried to show the physical inspection process. Each color represents one of the datum features and the little "X"s would be a probe point.

I'd like to know if what I've described above matches how you would interpret this print, and if not, what would you change on the print to capture the inspection setup described.
Thanks!

 

[KENAT]

cbrf23, do you have ASME Y14.8?

https://www.asme.org/products/codes-standards/y148-2009-casting-forgings-molded-parts

I don't look at it often enough to know off the top of my head but it may be of assistance, pretty sure it covers centering datums or whatever the term is.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[cbrf23]

Hi Kenat, I do not have a copy of that standard available.
I'll see if our supplier does and I'll try to get a copy purchased if there is any good info in there.

 

[3DDave]

Since you are locating from D, it should be secondary. B, C, and D should also have explicit extents to show how much of each feature they apply to. B and C seem to supply only an orientation so I would just drop the surface callouts and use datum targets.

 

[cbrf23]

Hi 3DDave. Datum targets do make more sense in this application, I will change my print accordingly. Thank you!

As far as the DRF hierarchy is concerned, I may be wrong here as I'm just going off the top of my head and not looking at the standard right now, but is the hierarchy not established based on the need for constraint? I.e. datum plane A is primary as it establishes my Z axis and Z location and restricts rotation about both the x and y axes, datum axis B-C needs to be secondary as it establishes the direction of my X and Y axes (relative to Z) and restricts rotation about the Z axis, and datum point D is tertiary as it only locates the part along the X and Y axes. I believe the basic dimensions must relate back to the DRF but I don't believe there is any requirement that the dimensioning scheme be related to the datum hierarchy in any way (again I don't have the standard in front of me right now to check).

 

[3DDave]

Each level constrains as much as it can constrain. [A] fixes 2 rotations (say X and Y) and a location (Z), [B-C] locates the part in vertically and fixes rotation about Z. [D] is left to only fix X.

Since there is no vertical dimension from B-C, the DRF is broken, unless you add in the complicated notation that was added in the '2009 version to un-fix constraints.

 

[cbrf23]

3DDave, I appreciate your comments, very helpful!

I think you may be right, I might need to use a custom DRF as I do not intend for B-C to control translational freedom at all, only rotational (establish direction of X and Y axes).
The intent is as follows:
Datum plane A restricts 3 degress of freedom: translational along Z, and rotational about X and Y
Datum axis B-C restricts 1 degree of freedom: rotational about Z
Datum point D restricts 2 degress of freedom: translational along X and Y

I'll add the callouts for constraint modifiers and that should do the trick.
Thank you!!

 

[cbrf23]

So I've found some examples of defining a v-block datum simulator using datum targets, but I haven't been able to find the section in Y14.5-2009 that explicitly explains this.
Does anyone have any reference for me on that?
The examples I found show the creation of a single datum feature using datum targets on two planes in a V configuration, such as what I've attached.

 

[cbrf23]

Nevermind - I found it in paragraph 4.24.5 and it is shown in figure 4-47. Perfect.