Another GD&T Question

[brandnew1]

Hi all,

i have another question regarding a hole location call out based on the feature control frame.

Based on the attached pdf i would like to confirm what is being asked for in terms of the hole in question.

It has a FCF of .005 M to datum D (area to the left when looking at the part from side), Datum G (regardless of feature size, which is the hole and Datum E (the line).
Datum G has a callout to be within .016 of datum D, E and F. i see the BASIC dimensions related to this location.
However for the hole in question, i see the BASIC dimensions off of Datum G but not Datum E.

So the question i have is, do i incorporate the values from Datum E (calculated values) or do i just focus on the location of the hole in reference to Datum G (since datum G already is based off Datum E)?

Greatly appreciate the help, thank you

 

[SteveMartin]

A cylindrical datum feature defines two planes (mutually perpendicular intersecting at its axis). The third datum in the FCF is used to orient these two planes.

Same spec (ASME 1994 Y14.5M), few pages later:
4.4.2
4.4.3 (and specifically figure 4-8)

 

[pmarc]

dtmbiz,
Please refer to my first post from 11 Nov 10. I described ther how the DRF is constructed. At that moment we were discussing about a little bit different drawing but that post applies also to current case.

I was trying to find a figure from Y14.5-1994 that would support my statement and I think fig. 4-7 does this. Para. 4.4.3(a) describes how this is technically done.

 

[dtmbiz]

I believe your ref's support my position, actually they do.
None of the examples show a DRF that does not have 3 planes that intersect. Three mutually perpendicular planes is the basic concept of for a DRF. In this example if the FCF omitted Datum E then you would be correct to say the DRF origin is datum G axis. It does not and therefore Datum E must be considered as one of the three DRF planes, resulting at the origin that was indicated in my post.


Additionally just because a cylinder represents a datum axis with 2 planes perpendicular to each other that intersect the axis, does not mean that all of the components (axis and planes) are used each time. See fig 4-8 pg 58 and fig 4-9 pg 59 in which two cylindrical features of size are used as secondary and tertiary datums. This fig shows only one plane of datum C being used and notice the DRF origin.


The whole point of this is that the drawing is not calling for what I speculate was hoped for as stated in my previous post. There are more clear ways to achieve the proper callout(s) relative to the mating part and function. I would need to understand that to offer any suggestion of course.


You have not answered my question as to how datum E is accounted for in the DRF “DGE” regarding your position that the DRF origin is the axis of datum G. My interpretation of your position is that you are good with a 4 plane DRF which is not at all a concept of this standard. Datum D is one; datum G accounts for 2 more and Datum E is another. And you did not support your position as to how datum E is accounted for in a gage setup.


Actually if you had a gage setup with a plate and pin representing Datum D and G respectively, and 2 gage pins to establish E and F; along with 3 more pins for the 3 holes referencing DRF “DGE” you will see that it doesn’t gain anything differently than referencing all from “DEF”; IMO.


Assertions and opinions are often interesting however to interpret drawings per the standard then the basic concepts are mandatory, unless an amendment to your particular company overrides one.

 

[pmarc]

dtmbiz,

You refered to figs. 4-8 & 4-9 from Y14.5M-1994. But unfortunately these figures are quite vague, so the committee decided to update them. When you take look at figs. 4-8 & 4-9 in 2009 edition of the standard you will see that the origin of DRF is exactly at the center of hole B. And this is exactly what I mean. Third datum feature is used only for constraining rotation of 2 datum planes associated with datum axis B.

And answering to your question - my interpretation of DRF "DGE" is that these are 3 not 4 datum planes: one planar D and two other associated with axis G. Datum E only tells us that two mutually perpendicular planes established by axis G are aligned to E. Origin of DRF "DGE" is at the center of hole G.

Sorry but I am not able to explain it better.

 

[dtmbiz]

Pmarc,

I will look at 2009 sounds interesting