Profile tolerance for outer rectangle surface

[Sa-Ro]

Hi

I need to control the outer surface of the rectangle wrt bore as shown in image.

Requirement: Outer surfaces to be equally located from bore center.

Does the drawing representation right?

Thank you

 

[3DDave]

J-P, no response on the defect?

I'll let B have his little world. My 40 year world included: USPS, an Italian postal suppler, USCG, USN, USAF, TACOM, IDF, New Zealand defense, Australia defense, a Swedish supplier of helicopter optical missile targeting systems, some bio-hazard containment tents, bio-hazard detection systems, and a stint with a supplier of bacterial propagation and detection systems for FDA approved diagnostic purposes. Maybe B just has bad suppliers.

 

[Burunduk]

And with all that experience in 40 years, you never encountered over-reliance on the title block plus-minus tolerance? Or maybe you also think it is as unambiguous as a general profile tolerance with a well-established functional DRF for controlling any non-critical locations and orientations of features?

 

[3DDave]

B does have bad suppliers.

 

[Burunduk]

Since you avoid answering, I conclude you also encountered such "bad suppliers" (and probably not just suppliers, why the focus on suppliers anyway?). The opposite would be unlikely in a 40 years career. Then it is just you not disagreeing, but having a problem with me bringing up that point from whatever weird an unexplained reason. Whatever.

 

[Belanger]

J-P, no response on the defect?

If you mean fundamental rule (l) referring to 5.1.1.4, which doesn't say anything about implied coincident centers, then yes it seems to be a goof. You can add that to your errata list.
I think rule (l) should refer to 5.8.3, which contains the often-overlooked rule buried in it about implied centers.

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

 

[3DDave]

J-P,

Seems like a nice add to training materials. I presume all these errors are included as a deltas packet for students to mark up and customize their copy of the standard.

5.8.3 is mainly concerned with zero position tolerancing at MMC and does not mention the implied zero dimension, so that would also require extensive rework.

Not a surprise given the rush job and limited public review of in-process work. It's like movies where something is wrong and the director says "fix it in post" but they never do.

 

[Burunduk]

Rule 4(l) says everything it needs to without the need to refer to any paragraphs dedicated to tolerancing of coaxiality, centrality, or coplanarity:
"...and geometric tolerances establish the relationship between the features" - that's all the information required.

 

[3DDave]

Thanks, B, for pointing out that not only was the reference wrong, it was unnecessary, an observation I already made.

Paragraph 5.8.3 says nothing about centrality, which is a term not used anywhere in the standard. It does use the deprecated term "symmetry."

The intent and usual use of such references is to give examples. Examples are about 70% of the volume of the standard. So, if one prefers to say "that's all the information required," then discard 70% of the standard and call it good.

 

[Burunduk]

You're welcome.

I prefer centrality as a design intent description instead of symmetry which can be confused with symmetry geometric tolerance.

Many things require an example, others are clear enough without one.

 

[3DDave]

The irony. When you argue both sides you lose.

 

[Burunduk]

What both sides? What are you complaining about now?

 

[Eric Gushiken]

I partially agree with others about also using the bore on the other end of the part so you could have a compound primary datum like A-B because the one bore is too short to stabilize the overall part. However, I would flip the datum scheme completely around and use the outer surfaces as my primary datums like you normally would and locate the center holes to that. That is how Manufacturing is going to make the part. They're not going to take a rough outer block, finish machine the center holes, then somehow hold the part by the center holes and finish machine the outer flat surfaces to that. That would be insane and a recipe for disaster. Then when you need to locate the small bolt holes you'd position them relative to the center holes. And for clocking you'd use outer surfaces as clocking datums at RFS.

As for Inspection, this works for them as well regardless if what kind of inspection tools and equipment they have. If they have Romer/Faro Arm they can check this easily. Even if they didn't have this equipment they could chuck the finished piece in a mill vice on the milling machine and use an indicator to check positions. You might even be able to use calipers to verify how centered the hole is relative to the outer surfaces.