First Post! Slot Boundary.... 3

[JMBofGA]

Hi everyone. Have a question regarding slot boundary. First, I am a CMM programmer and have this part to measure. I do not come across slots that often so when I do I normally question a few things. I will attach a image for you guys to check out. Obviously here I am checking the True Position of Datum C, but I see that there is a lack of a diametrical tolerance zone for the slot. So..

Question 1) What is the lack of the DTZ implying?
Question 2) How is the .8 applied and in which direction since the width of the slot stops rotation?

 

[pmarc]

First off, the diameter symbol is not missing in the position callout for the slot C. See fig. 7-34 in Y14.5-2009 and para. 7.4.5.1(c) - last two sentences in this paragraph in particular.

Also, fig. 7-34 shows how exactly the tolerance zone looks like, so I think this will answer your both questions.

Side note 1: If the width of the slot (9.65+/-0.15) is the datum feature for stopping rotation, then the datum feature C symbol, as shown, has been put in wrong place. It should be in line with one of the dimension lines of the dim. 9.65, or should simply replace one of the dimension arrows.

Side note 2: If you work to Y14.5M-1994, the same concept (with some minor modifications) is covered by para. 5.10.1(c) and fig. 5-47.

Side note 3: I see that you also posted this question on another forum where you were told that the presence of the diameter symbol inside the position callout for the slot would be okay. Well, it does not work that way. You can't just "reduce" both center planes derived from width and length of the slot down to a point or axis (as someone suggested) and check whether this point or axis falls within cylindrical tolerance zone, because then you will not be controlling orientation of the slot relative to the higher order of precedence datum axis B. In other words the actual slot will be absolutely free to rotate 360 degrees about its true position (which by the way also looks to be defined incorrectly on you print, because x=60 coordinate is not basic), thus be not fully defined.

 

[KENAT]

Lack of diameter implies it's a square tolerance zone.

Datum C looks poorly applied, I'd have thought being applied to the width (9.65 dimension invoking the center plane) would be better.

ASME Y14.5m-1994 Section 5.10 is the applicable area if drawing is to that version of the std.

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[drawoh]

JMBofGA,

The drawing is kind of weird.

"MAX DRILL POINT PERMITTED"??? Is there a side view showing the depth? This is an excellent example of how a section view makes things clear.

The word "BOUNDARY" has no official meaning to me. The drafter could be indicating that the positional tolerance applies all around the slot, in which case there should be a diameter symbol, as you noted.

My interpretation of datum[ ]C is that it has been applied to the radius at one end of the slot. This is legal as per ASME Y14.5, but not good practice. The 9.65[±]0.15 width would be a better datum[ ]C, controlling rotation of the part.

A good explanation for the lack of a diameter symbol is that the positional tolerance applied to a tertiary datum feature, works only in one dimension. Side to side positioning is defined by whatever datum[ ]C is.

Your 0.8 tolerance works to the left and right with respect to the round 9.65[ ]hole on the opposite end.

--
JHG

 

[KENAT]

drawoh, BOUNDARY is explicitly explained in Y14.5 - section 5.10.1C of the 94 version.

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[JMBofGA]

That's as I had thought myself, since the tertiary stops rotation and is always perfect to the CMM then it is basically a spread distance tolerance with a +/- .4

Edit: Yes there is a side view showing that these holes should have a depth of 6.5 +.2/-.5

 

[JMBofGA]

pmarc- can you elaborate on why the x=60 isn't basic?

 

[pmarc]

Ah, I took both 02s and the 03 as basic dimensions, which was kind of stupid because dimension values never have leading zeros, right?.

So if there is a note on a drawing stating that untoleranced dimensions are basic, then the x=60 coordinate is indeed basic.

My apologies for that.

 

[SeasonLee]

KENAT

It's really a square tolerance zone for Fig.7-28(09 Std) and Fig.5-41(94 Std) but not for the BOUNDARY tolerance, for the BOUNDARY tolerance zone see Fig.7-34(09 Std) and Fig.5-47(94 Std).

Season

 

[KENAT]

Seasonlee, I was referring to paragraph 5.10.1 C (last sentence) of Y 14.5 for interpretation of the actual FCF when I said 'square'. You're correct that once applied to the actual obround feature it's not square tolerance zone per se. Probably should have used the phrasing direct from the standard:

"Where the same positional tolerance can be allowed for both, only one feature control frame is necessary, directed to the feature by a leader and separated from the size dimensions."

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