Profile of surface Tolerances

[dross]

With the new chgs to ANSI Y14.5 1994, they have added a modifier to Profile tolerance calledUnequally Disposed Profile Modifier depicted by the symbol U within a circle.

The dimension that follows this modifier is the amount of the tolerance that is to be applied to "In-Space" (as opposed to In-material)

While a profile tolerance applied to the exterior of a part it is obvious that "in-space" would be a plus tolerance. What is not so obvious, at least to me, is where that "in-space" is when the tolerance is applied to a cavity within the part. Is "in-space" then to the interior of the cavity or the exterior? Does this change if the cavity it thru vs. blind?

I'm ordering a copy for the latest, but would like to know your opinions on this.

 

[dross]

114 views and not a single response!

 

[dr_gallup]

In space is away from the solid surface, does not matter if internal or external. In both cases it is adding material.

 

[Bob_W]

Ok, this was to be the second attempt to get my post submitted, but it ended up as an empty post. Now I am editing it and pasting my reply into this post. Hope it works this time.

Bob

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dross:

I'll try this again. I finished the reply and then went to submit but mistyped the captcha and lost the post. I actually did copy the entire post before I tried to submit, but forgot that just before I finished I moved a sentence using cut and paste and therefore lost everything else

As an example, if you have a profile tolerance of 0.25mm without a modifier the tolerance zone is symmetrical about the basic profile as expected. When you add the U modifier it permits you to shift the zone so that it may be fully inside the material or fully outside the material which is defined by the basic profile. The modifier will have a value between 0 and the profile tolerance limit. It will only be a positive value

When using the U modifier the value determines how much of the zone is outside the basic profile based on the opposite side represented as the material side.

Using the previous example with a 0.25mm profile tolerance zone, a U value of 0.0mm means that that the entire zone lies inside the basic profile on the material side (none of the zone is outside the material). A value of 0.10mm means that 0.10mm of the total zone is outside the basic profile, while 0.15mm is inside. And then of course if the modifier is 0.25mm the entire zone is shifted such the entire 0.25mm zone is outside the material.

I believe you may still use and dimension phantom lines on your drawing to graphically show the tolerance zone position if it not symmetrical.

Bob




Edited by: Bob_W

 

[dross]

Thanks for your replies guys.

I'm still not sure which side is the in material side for a blind cavity within the part.

I got a drawing from a customer that stated that the cavity should be on the plus side, but their drawing with the U modifier seems to imply that it is the opposite. I'm trying to determine if they made an error in the designation or not.

 

[Bob_W]

dross:

Do you have a picture you can post? A soccer ball, jar, and a funnel all have an internal 'cavity'. If the profile tolerance is on the outside surface of the ball for example, the material is toward the inside. If the profile is on the inside surface of the ball, the material side is toward the outside.

Bob

 

[dross]

Let's see if this works. I've removed sensitive information from the document.
The tolerance given seems to disagree with their note.View attachment 5799

 

[Bob_W]

dross:

From what I see, the profile tolerance zone lies completely within the open space indicated by the leader with a dot in the right view. No deviation would be permitted in the other direction. That would mean that the cavity can only get smaller based on the profile tolerance frame. This is due to the tolerance being .002 and the U value of .002 also.

Bob

 

[dr_gallup]

I agree, that is the "In Space" side.

 

[dross]

See their note, it implies the opposite.

 

[Bob_W]

Dross:

The note is hard to read, but I understand what you are saying. Having non ambiguous drawings is one goal of geometric tolerancing. This new method of creating profile tolerance seems to me to be an attempt at fixing something that wasn'nt broken. Using phantom lines as I mentioned in my previous posts would have made it perfectly clear what was desired. If you customer created the drawing, contact them and request clarification.

Bob