circular hole pattern as datum 2

[rhmeng]

I know there is a lot of discussion about holes for datums, i think i read them all, still a little confused. I have this part (see pic) that has 4 thru holes that bolts go through and meet up with tapped features on a different part. is the way i have it correctly dimensioned (only talking about the thru holes, datum A is the face the holes are on)? So the virtual condition of all of these holes will be diameter .144", with respect to eachother? The mating part has the tapped features dimensioned with a virtual condition of diameter .144" so i think i am fine. I am trying to understand how to think about it, or how it would be checked. Would you have 4 .144" pins at the basic locations and then see if this part fits over the pins and if it does its ok? Any help would be great. Thanks in advance

 

[powerhound]

Since the only relationship the holes have to A is orientation then you should change position to perpendicularity.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

 

[CheckerHater]

Will Perpendicularity control relationship between the holes?

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[pmarc]

Will not, that is why position shall not be changed to perpendicularity.

 

[greenimi]

I agree---AGAIN--- with pmarc.
I will just add that the simultaneous requirement will control the mutual relationship between the holes.

The gage pins should be at .150-.002-.004 = .144(virtual boundary / condition)

 

[rhmeng]

greenimi: thanks thats what I wanted to know, that when you check it 4 diameter .144" pins are used to check the mutual relation between the holes. So i think this is fine the way i have it, just need to add a "4X" before the diameter .150. On another note, when they use the gauge pins, how do they know that those are in the correct position relative to each other, or before they check the gauge pins how do they know they build the gauge fixture correctly?

 

[greenimi]

You have an inspection house or a certification lab to certify the gage against the gage print.

 

[Belanger]

Hang on -- according to the print I'm reading, there is only one hole being controlled. In that strict case, then the position symbol doesn't make sense.

But based on the title of this thread, I suspect there should be a "4X" on there somewhere. Then I would agree with you guys.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[rhmeng]

@Belanger:

So i think this is fine the way i have it, just need to add a "4X" before the diameter .150

thanks for the catch anywayrs

 

[powerhound]

Dang! Nothing much left for me to say. Yes, position is the way to go here. I should have thought about it more.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

 

[MQSCI651]

In my opinion, powerhound was right. Because of the FCF shows only one datum feature --- A, using perpendicularity makes more sense.
On the other hand, the distances among those holes should be specified with certain tolerances instead of basic dimensions, unless you define the center hole as a second datum, 4X holes or one of them as a third datum.

 

[powerhound]

The intent was all 4 holes to be a datum feature pattern and that's how I responded to the question. I just straight up screwed the pooch on this one.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

 

[Oaklandishh]

I am somewhat confused by this drawing.

If Datum A is the bottom face, why is true position being used?

How can Datum A control the holes positions relative to each-other?

What is controlling the angles between the holes, is that just not shown?

 

[Belanger]

OaklandDishh...even if datum A were not referenced, position would still control the holes' position to each other. This is simply by virtue of the 4X. Whenever 2 or more features are given a single position tolerance, they are automatically positioned to each other.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[greenimi]

Re:" How can Datum A control the holes positions relative to each-other?
What is controlling the angles between the holes, is that just not shown?"


Did i say---few days ago--:"I will just add that the simultaneous requirement will control the mutual relationship between the holes. "

Does not matter the angle, as long as it IS BASIC!!!

 

[Oaklandishh]

So the way it is now, it is sort of defined by polar cylindrical coordinates?

There is a tolerance zone 4 thou in diameter located at the exact location of the intended points?

What defines the zero orientation for the 45degree angle? is it the same thing?

 

[powerhound]

So the way it is now, it is sort of defined by polar cylindrical coordinates?

Polar is okay to use here.

There is a tolerance zone 4 thou in diameter located at the exact location of the intended points?

More like a .144 diameter boundary but essentially, yes.

What defines the zero orientation for the 45degree angle? is it the same thing?

Really, the 45 degree should be eliminated and everything else located with respect to the datum established by datum feature A the 4 hole pattern (B).

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

 

[MQSCI651]

What manufacturing sequence does this FCF suggest in this drawing?

 

[powerhound]

GD&T never dictates manufacturing sequence. It only dictates how the finished part is inspected.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

 

[greenimi]

Never say never:

Y14.5

The drawing should define a part without specifying
manufacturing methods. Thus, only the diameter
of a hole is given without indicating whether it is to be
drilled, reamed, punched, or made by any other operation.
However, in those instances where manufacturing,
processing, quality assurance, or environmental
information is essential to the definition of engineering
requirements, it shall be specified on the drawing or in a
document referenced on the drawing.