Doubt on Datum Callout 1

[Vimalmechs]

Hi all,

Recently i got a doubt on datum callout in a TOP GD&T frame. PFA.

Hope to hear back.
Vimal

 

[pmarc]

Vimal,
Yes, it may be reasonable to have reference to datum D in positional feature control frame for pattern of 4 dia. .266 holes.

Without it the pattern would be allowed to freely rotate around datum axis B (and that may be OK in certain applications). With D referenced the pattern must stay oriented to datum plane D. Or in other words an imaginary horizontal line connecting for example true centers of two upper holes of the pattern must be parallel to D.

 

[Vimalmechs]

Hi Pmarc,

Rotation of the dia.266 holes are arrested by 3.500 boundary circle, 45deg and EQ. SPACING.

As well If the hole location is by DATUM D, there should be basic dimension from DATUM D to dia.266 in this figure. it is not shown.Adding up of those dimension result dimension redundancy.

Based on top level assembly functionality, the rotation of the holes dia.266 with "hole B" doesn't effect the assembly function (rotation is OK in this application).

Hope to hear back,
Vimal

 

[CheckerHater]

Let’s clear something up, Vimal.
You say “the rotation of the holes dia.266 with "hole B" doesn't effect affect the assembly function”, and then “Rotation of the dia.266 holes are arrested by 3.500 boundary circle, 45deg and EQ. SPACING.”
So, either it’s relevant, or it’s not, and you choose to constrain the holes. Also, EQ SPACED is no longer supported per 1994 and latest standard. So, the hole has to be constrained by different means.
Next, you say “As well If the hole location is by DATUM D, there should be basic dimension from DATUM D to dia.266 in this figure.”
I am afraid you don’t quite understand how it works, because YOU DO HAVE BASIC DIMENSION FROM DATUM D TO DIA .266.
Your .266 holes are dimensioned by chain of BASIC dimensions 2.779 from datum D, hole circle diameter 3.500, and 45 deg. angle. Like I said, EQ. SP doesn’t cut it anymore. You have to specify 4X 90 deg, or rely on implied basic 90 deg, but you’ll have to draw radial centerlines first.
So, at least one of your .266 holes has basic dimensions tieing it up to datum D.
If you are still not convinced, just ask yourself a question: 45 deg. to what?
You cannot measure angle from round hole. You have to use some reference to establish your imaginary horizontal line and that reference is called a DATUM.

 

[Vimalmechs]

Hi CH,

Primarily, i am agreeing with you, i have to dimension with quantifier instead of "EQ. SP" and radial center lines.

Secondarily, by considering my function the free rotation of dia.266 hole pattern(with tapped holes)is acceptable. i am marking to remove D datum, add dimension with quantifier, remove 45deg and some other modifications.

thank you for the help,
Vimal

 

[pmarc]

CH,
Sorry for being off topic, but it is the second time in recent posts that you are saying something similar to:

Also, EQ SPACED is no longer supported per 1994 and latest standard.

Well, it is not true. At least Y14.5 does not clearly prohibit use of EQ SPACED or similar note, abbrevation. Just see fig. 4-38 of Y14.-2009 - EQLSP is there.

 

[CheckerHater]

pmarc,
It is definitely off-topic, but 4-38 is missing circular pattern and diameter as well, so it is highly questionable if EQSP would ever make it into complete drawing.
Also, Appendix A10.6 states that “X symbol has replaced the note designation”, so by the rules of English grammar “note designation” is the thing of the past.
And since when "does not clearly prohibit" means "supports"?
If the book says "shall", "should", or at least "may" it supports. If it doesn't say anything, it doesn't support.
By your logic the standard book should prohibit infinite number of things, which is impossible logically and physically.

 

[pmarc]

CH,
And again we have the same kind of discussion.
Before refering to A.10.6 I would strongly recommend reading it carefully. It really has nothing to do with English grammar. It is just a matter of reading with understanding. In this particular case we are talking about pattern of features of size, you are refering to a place in the standard talking about SURFACES. And please do not even try to convince me that a hole (or pattern of holes) shall be considered as a cylindrical surface (or group of surfaces) in this case. I won't buy it.

 

[CheckerHater]

Are you serious?
If you read A.10.6 carefully, you'd notice that it says "for example, surface".
Are you implying that, according to Y14.5, X, when used as a multiplyer, only applies to surfaces?

 

[pmarc]

I am saying the X replaced text note. It could have been 2 SURFACES as well as 3 SURFACES, 10 SURFACES, 100 SURFACES. That is why the standard used "for example". Just compare fig. 8-14 ('09) with 6-20 ('94). That is all what A.10.6 is about.

 

[CheckerHater]

No more questions

 

[pmarc]

No more questions

Could you be more specific? Did this convince you or on the contrary - do you keep claiming that EQLSP "is no longer supported per 1994 and latest standard" and has been replaced by X?

 

[Gilmiril]

I would agree that A.10.6 is referring specifically to surfaces, but it is also only listing the changes between the 2009 and 1994 standards. Using #X to designate the number of holes was already in use in the 1994 standard. (Also, why shouldn't a hole be considered a surface?)

That said, the standards (both 1994 and 2009) use 'may' not 'shall' in paragraph 1.9.5, which suggests other ways can be used. But no alternative is given, and the examples consistently use #X, so this is certainly the preferred way.

The number one goal of drawings is to communicate information with maximum clarity while using the most concise 'language' possible. In my opinion, using #X (together with an angle) is both more clear AND more concise than the old '# HOLES EQL SP' notation. But everyone has their own opinion.

 

[pmarc]

Gilmiril,
I think everyone here, including me, will agree that #X and basic angle "is both more clear and precise" than the EQLSP. There are however cases, and in my opinion fig. 4-38 in Y14.5-2009 is one of such, that EQLSP (or similar note) is sufficient and does not introduce any ambiguity.

(By the way, with EQLSP notation one still needs #X).