Profile tolerance w/ reference datums dimensioned from non-datum edges?

[TolQ]

I'm inspecting a part which is toleranced in a way I have not encountered before. I believe the method used is incorrect, but I'd like a second opinion.

As you can see the untoleranced dimensions are basic, but they are not dimensioned from the datums called out in the profile tolerance FCF.

In this situation how would you apply the profile tolerance to the location of the two untoleranced holes?

 

[ewh]

Sorry, can't see pic (host blocked by company).

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[drawoh]

TolQ,

Datum[ ]C is called up twice, which is wrong. Given that datum[ ]C is tertiary, only one slot should be a datum.

There is no dimension from the edge to the datum slots, and there is no positional tolerance on your holes. Maybe these are on another view on the drawing. Showing the dimension from the edge, rather than from the datum feature, is poor drafting practice, but it is not wrong. If there is a dimension from the slot to the edge, and there is a positional tolerance, you can inspect it. The positional tolerance works from the slot, not from the edge.

--
JHG

 

[TolQ]

There is another view which gives enough information to determine the location of the holes relative to the datums. You're saying that I should inspect this using the 0.1 Profile tolerance from the datums, not the edges they are dimensioned from? There are no tolerances for the holes beyond the profile tolerances shown.

 

[drawoh]

TolQ,

I note that you have a default hole tolerance. Are they countersunk or centre bored? In the absence of a positional tolerance, your profile tolerance controls the position of the holes.

Yes, the profile tolerances work from the datums, not from the non-datum edge.

--
JHG

 

[TolQ]

The holes are counterbored. I figured measuring from the datums was correct, one of our machinists disagreed with me on it so I figured I'd get a second opinion.

Thanks

 

[JNieman]

You say "As you can see, untoleranced dimensions are basic" but I do not see that your conclusion is accurate, without more information. Is there a default tolerance standard called out of some kind? Such as an ISO category/class (I forget the right term, sorry, I don't deal with ISO nearly as often)?

What I'm gearing at is: I don't necessarily know that a dimension without a direct tolerance applied to it is basic. I only know that it does not have a direct tolerance contained within the dimension value. With a small cutout from a print, I do not know whether there is more relevant information or not.

There's two interpretations I see:

1) Yours, if there is no other clarifying information, is correct
or
2) There may be a note somewhere clarifying the 'default' tolerances based on decimal points or 'size' of number, depending on how the company decided. In this case, "untoleranced" would only refer to those features which are not dimensioned, such as that curvy cutout in the middle, the length of the full-round slot, and the distance of the slot from the edge, which must be measured in regards to the datum alignment A|B|C, as specified., and the other dimensions are measured exactly as shown.

 

[TolQ]

JNieman, you must not have seen the section at the bottom of the image where it states the profile tolerance and says "Untoleranced dimensions are basic".

The only default tolerance information on the drawing is what is shown at the bottom of the image.

I did not include the entire drawing, the center feature is dimensioned elsewhere on the drawing, I simply provided this as a sample as the holes are the most obvious example on the drawing of a set of features with no tolerancing beyond the profile tolerance shown.

 

[djhurayt]

lower left corner

Untoleranced
dimesnions
are basic:

 

[JNieman]

I saw and understood the note. I was just pointing out a common drawing tolerance method that may have been overlooked. Like I said. If that really is the entire picture, I agree with the others: you're right. I thought it was worth mentioning a common situation where the machinist would be right, if it applied.