Continuous feature of size per Y14.5M-1994

[pmarc]

I guess my general question is short: "How would you specify continuous feature of size on a print governed by Y14.5M-1994?"

Let's say I want to control total runout of an external cylinder containing an interruption (O-ring groove for instance) relative to a datum axis. How would you indicate on a drawing that both parts of the cylinder, in addition to the total runout requirement, must not violate single MMC envelope defined by Rule #1?

Thank you.

 

[fsincox]

Please reference the section of the 1994 standard that says position with no datum is prohibited. Naturally, I don't agree with them.
Frank

 

[greenimi]

5.2.1.3 Identifying Features to Establish
Datums. It is necessary to identify features on a
part to establish datums for dimensions locating true
positions. For example, in Fig. 5-2, if datum references
had been omitted, it would not be clear whether
the inside diameter or the outside diameter was the
intended datum feature for the dimensions locating
true positions. The intended datum features are identified
with datum feature symbols, and the applicable
datum references are included in the feature control
frame. For information on specifying datums in an
order of precedence, see para. 4.4.



5.2 POSITIONAL TOLEBANCING
A positional tolerance defines:
(a) a zone within which the center, axis, or center
plane of a feature of size is permitted to vary from
a true (theoretically exact) position; or
(b) (where specified on an MMC or LMC basis)
a boundary, defined as the virtual condition, located
at the true (theoretically exact) position, that may not
be violated by the surface or surfaces of the considered
feature.
Basic dimensions establish the true position from
specified datum features and between interrelated
features. A positional tolerance is indicated by the
position symbol, a tolerance value, applicable material
condition modifiers, and appropriate datum references
placed in a feature control frame.

 

[greenimi]

versus 2009 which states:

7.2.1.3 Identifying Features to Establish Datums. It
is necessary to identify features or features of size on a
part to establish datums for dimensions locating true
positions except where the positioned features establish
the primary datum. (The exception is explained in para.
7.6.2.3.) For example, in Fig. 7-2, if datum references had
been omitted, it would not be clear whether the inside
diameter or the outside diameter was the intended
datum feature for the dimensions locating true positions.
The intended datum features are identified with
datum feature symbols, and the applicable datum feature
references are included in the feature control frame.
For information on specifying datums in an order of
precedence, see para. 4.10.

7.2 POSITIONAL TOLERANCING
Position is the location of one or more features of size
relative to one another or to one or more datums. A positional
tolerance defines either of the following:
(a) a zone within which the center, axis, or center
plane of a feature of size is permitted to vary from a true
(theoretically exact) position
(b) (where specified on an MMC or LMC basis) a
boundary, defined as the virtual condition, located at the
true (theoretically exact) position, that may not be violated
by the surface or surfaces of the considered feature
of size.
Basic dimensions establish the true position from
specified datums and between interrelated features. A
positional tolerance is indicated by the position symbol,
a tolerance value, applicable material condition modifiers,
and appropriate datum references placed in a feature
control frame

 

[fsincox]

Greenmi & pmarc,
Yes, this is the thread, I disagree with your conclusion, I do believe you are reading too much into it to take this as a prohibition. None may be “applicable” or “appropriate”, and they will be located by datums in earlier lines.

 

[gabimo]

"The only thing that is required in the 1994 standard for the position control is that there be "at least one" datum reference, and the committee eventually realized that even that statement was in error since it is perfectly possible to have a true design requirement where the orientation/location of a pattern (i.e. more than one) might need to be controlled just to each other, and not to any DRF. In fact, there are even examples of such controls in the 1994 standard." Mark Foster from:

http://www.linkedin.com/groups/How-calculate-true-position-one-1781397.S.110469884

 

[pmarc]

Frank,
I never said that single segment position FCF without datum feature references was prohibited.

 

[gabimo]

Frank,
Ref: Mark Foster:

In addition to my first post: "
"The only thing that is required in the 1994 standard for the position control is that there be "at least one" datum reference, and the committee eventually realized that even that statement was in error since it is perfectly possible to have a true design requirement where the orientation/location of a pattern (i.e. more than one) might need to be controlled just to each other, and not to any DRF. In fact, there are even examples of such controls in the 1994 standard." Mark Foster from:

http://www.linkedin.com/groups/How-calculate-true-...

Here is the second post:
" Certainly position with no datum references would work for the control of coaxiality, but would have no effect on form. Position without datum references was prohibited in the 1994 standard (although most people did it anyway when it made sense, and there was even an example of it in the FRTZF of a composite position in the 1994 standard), but it is explicitly allowed, complete with an example of it, in the 2009 standard." from Mark Foster:

http://www.linkedin.com/groups/ABC-..._list-0-b-ttl&goback=.gmr_1781397.gna_1781397

I don't think Mark Foster needs any introduction....

greenimi and pmarc,
Did I "save" you?

 

[pmarc]

gabimot,
I know Mark - he is great GD&T expert and great guy.
I also know Alex Krulikowski - he in turn is a member of Y14.5 committee. The attached snapshot comes from his book "Advanced Concepts of GD&T", 7th edition, which bases on Y14.5M-1994 standard:

http://files.engineering.com/getfil...5ae3-4be0-87d0-fa2ac62027b4&file=position.png

Who is right? I do not know. And this is what I have been trying to point out in this and in other threads - there is no clear answer. Fortunately, this confusion has been clarified in '09 edition of Y14.5. Unfortunately, there are still maaaaany companies following Y14.5M-1994 or even earlier versions, so this kind of debates will be happening from time to time.

 

[fsincox]

As long as we all realize they were wrong, obviously, I did not see it then. Frank

pmarc,
In our discussion on my keyway example, IMHO, your crowning point was in essence your reference to the current datum relationship requirements in 2009, despite the fact my example and the referenced standard would be 1982, why then is 2009 not good enough to settle it, now?
Frank

 

[fsincox]

gabimot,
Thanks for the information update.
Frank

 

[pmarc]

Frank,

Because what you are trying to achieve in your example (that is to locate the keyway through 2 parallelism callouts applied to its side walls AND by assigning the keyway width as secondary datum feature B) does not meet requirements defined in 2009. Your parallelism callouts do part of the job only - they orient, but do not locate, whereas for such configuration of datum features secondary datum feature (that is keyway width) shall be controlled for ORIENTATION AND LOCATION relative to primary datum axis.