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Profile of a Line and Position (Boundary) Together Legal? 1
- Thread starter Tarator
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- #21
You mentioned "My concern was profile of a line is a 2D control, where position is a 3D control. However, logically, the curve edge is an irregular feature of size, and position should be able to control the location"
If you are attempting to control only the sharp edge then add a note that states the controls apply only to the edge. Otherwise it will appear to apply to the full depth of the feature, in which case it does not completely control the clearance surface, for reasons already mentioned.
You might also use a conventional profile tolerance and boundary position tolerance combination with a note that it only applies to some small amount of depth, which is true because no edge is infinitely sharp.
Presumably a more complete drawing would have shown the control you have in mind for the remainder of the clearance surface, to avoid that as a red herring.
If you are attempting to control only the sharp edge then add a note that states the controls apply only to the edge. Otherwise it will appear to apply to the full depth of the feature, in which case it does not completely control the clearance surface, for reasons already mentioned.
You might also use a conventional profile tolerance and boundary position tolerance combination with a note that it only applies to some small amount of depth, which is true because no edge is infinitely sharp.
Presumably a more complete drawing would have shown the control you have in mind for the remainder of the clearance surface, to avoid that as a red herring.
pmarc
Mechanical
- Sep 2, 2008
- 3,248
For what is worth, here are my loose thoughts on some aspects of this discussion. This probably won't bring anything new, but hopefully will strengthen some opinions:
1. I agree with Evan that position tolerance can be used in case of tapered features, even when the feature is non-uniformly tapered. Such feature, if fully defined for its size and form (through profile of surface tolerance), falls under definition 1.3.32(b) - irregular feature of size type B - where the shape of the envelope contained within this feature is simply "other than a sphere, cylinder, or pair of parallel planes". I am not saying this is the best approach to tolerance such features, I am just trying to say that this technique is valid and mathematically interpretable.
2. Assuming that only the profile of a line / position combination is applied to this fancy-shaped hole, this is not legal callout. Profile of a line itself is not capable of controlling size and form of the feature depth-wise. Thus, even without going into details on whether it applies to specific single slice or to multiple slices of the feature independently, this combined callout violates one of the fundamental rules of dimensioning and tolerancing as defined in para. 1.4(b) - not every characteristic of the feature is fully defined. The deck of cards example is absolutely spot-on.
3. Like it was said, by default profile of a line callout applies to the entire depth of the feature, unless otherwise specified. Therefore, if the intent is to apply the profile of a line requirement just to a single slice or to restricted depth of the feature, it must be clearly stated on the drawing. And by analogy the same applies to the position callout. But even if it is done, the rest of the feature must be somehow controlled in order to avoid incomplete definition of feature's geometry.
1. I agree with Evan that position tolerance can be used in case of tapered features, even when the feature is non-uniformly tapered. Such feature, if fully defined for its size and form (through profile of surface tolerance), falls under definition 1.3.32(b) - irregular feature of size type B - where the shape of the envelope contained within this feature is simply "other than a sphere, cylinder, or pair of parallel planes". I am not saying this is the best approach to tolerance such features, I am just trying to say that this technique is valid and mathematically interpretable.
2. Assuming that only the profile of a line / position combination is applied to this fancy-shaped hole, this is not legal callout. Profile of a line itself is not capable of controlling size and form of the feature depth-wise. Thus, even without going into details on whether it applies to specific single slice or to multiple slices of the feature independently, this combined callout violates one of the fundamental rules of dimensioning and tolerancing as defined in para. 1.4(b) - not every characteristic of the feature is fully defined. The deck of cards example is absolutely spot-on.
3. Like it was said, by default profile of a line callout applies to the entire depth of the feature, unless otherwise specified. Therefore, if the intent is to apply the profile of a line requirement just to a single slice or to restricted depth of the feature, it must be clearly stated on the drawing. And by analogy the same applies to the position callout. But even if it is done, the rest of the feature must be somehow controlled in order to avoid incomplete definition of feature's geometry.
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