Designer's intent to control position, concentricity or ..

[SeasonLee]

Just receive a drawing today, but I am confused on the designer’s intent, I am not quite sure what he want to control, Position? Concentricity? Coaxiality? Or…

There are some errors on the print, but I want to know the meaning on the arrow indicated, thanks in advance for all comments.

SeasonLee

 

[pmarc]

SeasonLee,
Before anything, what is the projection angle for this drawing? I am probably missing something, but are those views shown correctly? Is there a chance to see 0.265 feature's geometry from the right?

 

[EngineerErrant]

http://www.aps.anl.gov/APS_Engineering_Support_Division/Design_and_Drafting/DDStandards/fig6_6.gif

Absolute position of the central axis relative to datum A and B must be held within 0.005 of the "exact" position.

"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." -Scott Adams

 

[fsincox]

My guess is he is controlling directional position(coaxiality). I suspect the 0.55 diameter should have a diameter symbol added.
Frank

 

[SeasonLee]

pmarc

The .265 is just a mill surface as shown on the photo

EngineerErrant

Thanks for your comment, but I have question on the other feature Ø.3107/Ø.3113 position callout if the flat feature .265 position callout is coaxilaity control

By the way, its Y14.5 standard.

SeasonLee

 

[drawoh]

SeasonLee,

It looks like he is using true position to control the flat on his shaft. Since this is not a feature of size, this is an error. A profile tolerance on the flat would have worked fine.

You could treat the specification as a profile tolerance.

Better yet, you could call the drafter and ask them to explain, thus showing off your mastery of GD&T.

--
JHG

 

[fsincox]

JHG,
It passes "the caliper test" in my opinion. Your definition must have more to it than that then. That is exactly the problem with unoffical, official standard definitions.
Frank

 

[powerhound]

I believe the spec on the right end of the part is incorrect. While the .265 is definitely a feature of size, the feature is not centered on datum axis A. There should be a profile callout to the flat with a basic dimension from the center of datum axis A. Also, calling out datum B serves no purpose.

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2010
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[pmarc]

SeasonLee,
Regardless whether the feature is FOS or not, positional tolerance applied to 0.265 dimension controls something which is not coaxial with datum axis A. So the arrow indicated callout is only able to control position, not coaxiality or concentricity. In that case basic dimension from datum axis A to the center of the feature is missing. (BTW, I am not sure why you asked for concentricity since this characteristic has its own symbol and interpretation in Y14.5)

The other thing is that in my opinion this positional callout should not be there at all. Like it was already stated by others, flat should be rather controlled by profile callout relative to datums A and B (for that basic dimension from datum axis A to the flat would be needed), and the remaining portion of ø0.3107-0.3113 cylinder by position callout ø0.002 as it is shown in bottom view of your original print (the diameter symbol before position tolerance value is missing at the moment). Really nothing more would be required. In that case coaxiality of axis of the cylinder with datum axis A, which is a special case of position, would be controlled.

 

[SeasonLee]

Thanks for all your comments, will contact with the designer to clarify his intent.

SeasonLee