Profile Basic Dimensions

[Jacob Cheverie]

I have attached an image of a particular situation that I am wondering about. As can be seen, there is a profile of a surface tolerance on a small arc with respect to datum features B and A. My question is in the validity of the current dimensioning scheme.

The profile is from point X to point Y. There are basic dimensions defining the location of X, the location of Y, and the radius of the arc. The locational basic dimensions are with respect to the datum structure. In my opinion, this should be sufficient to define the tolerance zone. Is that correct?

An alternative method would be to locate the center of the arc itself with basic dimensions and assign a basic dimension to the radius. Is this method valid? If both are valid, would this method be preferred due to it's greater simplicity?

 

[Burunduk]

In both cases the true profile is fully defined relative to the datum reference frame, so yes both ways are valid. I would also prefer the second scheme that basically locates the radius center of the arc outline. And you don't even need the X and Y labels because profile applies by default to the single feature to which the leader from the FCF points and the curved surface of revolution is a unique feature with a clear extent.

 

[Burunduk]

One thing some will be telling you is that the datum feature symbol for A should either be placed aligned with the diameter dimension line or on the surface in a view where the outline is circular. It appears that some may interpret the placement of the datum feature symbol as shown as applying to a longitudinal line element on the surface as the datum feature(!)
thread1103-474128

 

[greenimi]

Burunduk and all,

Looks like the issue raised by the OP is wrapping up.
I would like to ask my own question related with this drawing: pretend the OP's part is symmetrical to the vertical right face/ opposite face from the datum feature B.

Can we use 2X profile| xxx|B|A| and in between X<-->Y to cover both ends?
Or we need another "in between" symbol and another profile symbol for the right end?

 

[Jacob Cheverie]

Thank you Burunduk,

I also agree that the second method is more direct. Unfortunately, I was the one to propose the first method. Then again, I am not a designer so I am glad to hear that it is equally valid. When speaking to the designer about this part, they also brought up the issue of the datum feature symbol for datum A. I looked through the thread that you linked and I agree, with some of the others in that thread, that the way that it is labeled is referring to the surface of the cylinder. That would imply that the cylindrical surface is the datum feature. In an RFS situation, we would use the resolved geometry (the axis) and in an MMC situation we would use the surface interpretation in the event of a significant difference.

 

[Burunduk]

Jacob Cheverie,
I think that when equivalent basic dimensioning schemes that lead to the same specifications are considered, it is perhaps best to specify the most convenient basic dimensions for manufacturing/inspection needs. Your proposal may have its advantages. I look from the design perspective.

greenimi, to your follow-up question, the problem with specifying the profile with the 2X notation and with reference to |B|A|, is datum feature B. Datum feature B is the left side end face. For the right side of the symmetrical version of this part as you describe, possibly a different datum reference identification, referring to the right end face, would make sense (with a different letter). It would require a separate profile FCF. If you just specify 2X per your question, it would create a reference to the left end face as a datum feature for the right side profile control. It would also create a pattern between the 2 sides. Also maybe it could be questioned whether the X and Y labels would be implied to apply symmetrically. It's not described in the standard.

 

[greenimi]

the problem with specifying the profile with the 2X notation and with reference to |B|A|, is datum feature B. Datum feature B is the left side end face. For the right side of the symmetrical version of this part as you describe, possibly a different datum reference identification, referring to the right end face, would make sense (with a different letter). It would require a separate profile FCF. If you just specify 2X per your question, it would create a reference to the left end face as a datum feature for the right side profile control. It would also create a pattern between the 2 sides. Also maybe it could be questioned whether the X and Y labels would be implied to apply symmetrically. It's not described in the standard.

Ok. That is fine.
My basic question was (and still is) if you think 2X (or nx multiplier) can be used with "in between" symbol?
I don't know if I've seen a good case for such method.

Did you?

 

[aniiben]

Can you use multiple in between symbols one in top of the other? Then each will have its own separate features to be applied to and because of multiplier note will make a pattern.

 

[Burunduk]

greenimi,
There is a specific type of cases for which nX with a profile tolerance associated with the between symbol can and even should be used. The condition for this to be feasible is that it is very clear from the part geometry where the letter-designated locations related to the between symbol should be duplicated. I'm talking about profiles that are repeated in symmetrical patterns. An example could be this part, recently discussed in another thread which has a group of periphery surfaces around each bolt hole repeated n times in a circular pattern. A detail view could show the outline of one such section with profile of a surface applied with the between symbol and the number of places specified.