TP FCF on a Hole Note Applies to Which Feature? Thru Hole or C'Bore?

[ModulusCT]

So my supervisor tells me yesterday that in the attached example, the way it's written, the machinist will basically just be able to choose on his own which part of the hole to apply the positional tolerance to. Is that correct? I was under the impression that a thru hole with a c'bore shared a C-Line and therefore the positional tolerance would control the shared axis of both parts of the hole and therefore control both features simultaneously... Would I need a FCF for each aspect of the hole note??? Drill or tap thru/FCF/Cbore/FCF/ancillary info? That doesn't sound right to me...

Thanks for the feedback.

Mod

I'm not a vegetarian because I dislike meat... I'm a vegetarian because I HATE plants!!

 

[Belanger]

According to paragraph 7.4.2 of the standard, it looks like you are right (same position applies for thru hole and c'bore or whatever).
BTW, the position tol should have a diameter symbol in front of the .004.

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

 

[CheckerHater]

The same tolerance (.004, but better ∅.004 as JP mentioned) applies to both axis of hole and axis of counterbore, BUT hole and counterbore do not share the same axis.
Also, hole diameter tolerance is specified, but c-bore tolerance isn't (possibly relies on titleblock). If c-bore tolerance is different from hole tolerance, virtual conditions will be different as well.

 

[ModulusCT]

7.2.4 Does indeed describe my situation exactly. Thanks for the info! This will be very helpful....

I'm not a vegetarian because I dislike meat... I'm a vegetarian because I HATE plants!!

 

[ModulusCT]

"The same tolerance (.004, but better ∅.004 as JP mentioned) applies to both axis of hole and axis of counterbore, BUT hole and counterbore do not share the same axis.
Also, hole diameter tolerance is specified, but c-bore tolerance isn't (possibly relies on titleblock). If c-bore tolerance is different from hole tolerance, virtual conditions will be different as well."

Thanks guys - forgot to mention -

1) Add dia. symbol, check.
2) .xxx = ±.005 in title block for the c'bore tol.
3) What do you mean, the c'bore and thru hole do not share the same axis?

I'm not a vegetarian because I dislike meat... I'm a vegetarian because I HATE plants!!

 

[KENAT]

3) Within the .004 pos tolerance the axis of the c'bore and hole can shift relative to each other.

In ASME Y14.5M-1994 the section is 5.7

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[CheckerHater]

The perfect theoretical axis will be the same.
Two tolerance zones will be constructed around theoretical axis. Bonus tolerances (different for hole and counterbore) will be added.
Then axis of hole will be free to shift/tilt within its own tolerance zone, and axis of c-bore will be free to shift and tilt within its own tolerance zone. That's what I meant saying "don't share axis" - there will be no common axis shifting and tilting within common tolerance zone.

 

[ModulusCT]

I understand now... Thanks for clearing that up for me. It seems that two FCF's might be in order especially since the c'bore is a clearance hole feature.

I'm not a vegetarian because I dislike meat... I'm a vegetarian because I HATE plants!!

 

[CheckerHater]

As long as mating part will fit thru, you may get away with single FCF. It's all in the function.
Two separate FCFs will mean your QC will set two procedures to check holes and counterbores separately. Is that any better?
And also, if the most important to you is to relate every c-bore to its own hole, there is the THIRD way to tolerance: you make your hole a datum and control c-bore wrt that datum. Just don't forget to call "(number of holes)X INDIVIDUALLY" (see Fig. 7-26)
Good luck!

 

[3DDave]

What's the c'bore clearance for?