What's the diameter? Indirect dimensioned with offset from a circular feature with g6 tolerance 2

[Perka]

This is probably very basic stuff, but can someone point in to some rules of how to interpret a drawing like this?
What diameter to expect. See attached pdf.

 

[Belanger]

That smaller diameter cannot be determined, because that 1 mm dimension (lower part of View A) is a result of the smaller cylinder's diameter but also the location tolerance between the two diameters (coaxiality). So you'd have to provide some tolerance such as GD&T position for the answer to be determined.

edit: You should also probably tell us what dimensioning standard is being invoked (ASME vs. ISO), because the roundness of the diameter may also come into play.

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

 

[cr7]

...(ASME vs. ISO),

It's written ISO 2768-fK at the bottom.

I don't have an answer though. And I think it is not as basic question as it looks at first.

 

[CheckerHater]

What if diameter is irrelevant and 1+/-0.05 REALLY is dimension to be controlled?

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

 

[Belanger]

cr7 -- thanks; on my screen I didn't scroll down to that. So here's what my copy (from BS-EN 1993 version) of the 2768-2 standard says:

5.2.5 Coaxiality
"General tolerances on coaxiality are not specified.
NOTE: The deviation in coaxiality may, in an extreme case, be as great as the tolerance value for circular radial run-out given in Table 4, since the deviation in radial run-out comprises the deviation in coaxiality and the deviation in circularity."

and Table 4 tells us that, for your tolerance class K, that the radial runout can be up to 0.2.
But then there's another hiccup to this. Paragraph 5.2.6 says that, for this type of unspecified runout, "if the features are of equal nominal length, either may be taken as the datum."
Both of these cylinders have a length (depth) of 5 mm, so there could be two readings.

I agree that it's too shaky of a question. But let's see what other folks have to say.


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

 

[Tmoose]

If that was a journal that a ball or roller bearing was to be installed on the diameter (g6 in your case) would be the tolerance for the basic diameter.
Implying anything from the g6 diameter tolerance about that journal's roundness or cylindricity or it's runout or coaxiallity with any other features would be wrong.


The roundness, cylindricity etc would typically be controlled to a tighter tolerance, controlled by one of the ISO 286es. Please see attached png image.
The reaason being, if the diameter of a "perfect" journal gets larger or smaller it just changes the bearing's internal clearance.
But poor roundness or cylindricity causes poor load sharing and running accuracy, which clobbers the bearing L10 fatigue life etc and increases noise.

I suspect, but do not know, that those IMPORTANT relationships have not migrated automatically and gracefully into the various GD&T standards.
Actually my hunch is that the bearing shaft and housing tolerances require several extra feature control frames to over-ride the urge to make implications of the tasty and vulnerable target that is the diameter tolerance.