Can True profile dimension be outside the Profile tolerance zone 1

[prabhakardesign]

Hello,

Wether Profile tolerance can be given to a surface, for which the Basic dimension should be outside the profile tolerance zone.

For a size dimension 50 +2/+1 can we provide unilateral profile tolerance. The mean value is 51.5, and nominal value is 50 (Upperlimit is 52 and lower limit is 51)

This is a unilateral profile tolerance, but the true profile lies outside the Profile tol zone.

Whether the above dimn can be used shown with Profile of Surface callout ?


How the callout can be made for profile?

Please provide your suggestion

Thanks and regards,
Prabhakar

 

[dingy2]

The true profile should show the theoretical location of the feature with the profile of a surface or line tolerance indicating whether the tolerance value is a bi-lateral or unilateral tolerance.

So, the true profile cannot be outside the tolerance zone.

Dave D.

http://www.qmsi.ca

 

[Belanger]

I agree with Dave. While the world of plus/minus tolerancing allows for a nominal value to be outside of the actual range, the world of GD&T does not allow that. So profile tolerances can be unilateral, but nothing further than that.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[fcsuper]

John,

I would disagree with the statement of +/- tolerances, at least with ASME. The absolute limits are the top and bottom of the +/- range. No part of the controlled feature can fall outside that boundary, same as GD&T.

Matt Lorono, CSWP
Lorono's SolidWorks Resources & SolidWorks Legion
Follow me on Twitter

 

[Belanger]

Matt -- I was assuming that the OP was outside the US, I guess. Many other countries use the ISO system of limits and fits, which use letters and numbers (f7, g8, etc.) as code language, but that code often translates to plus/plus and minus/minus tolerances.

See Fig. 6-13 in the 2009 edition of Y14.5, where it gives the dimension of 16f7. We could call that pin a nominal size of 16, even though the real limits don't include 16.

Also, as a disclaimer, I don't like the plus/plus or minus/minus deal. I'm just telling how some people do things.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[pmarc]

I am basically with Dave and J-P on this.

However I am curious of your thoughts about following:
Take a look at fig. 8-27 in Y14.5-2009. (I know we debated about it some time ago and there were different opinions on mixing coordinate dimensioning with profile callouts). If you put 50 +2/+1 dimension instead of 80 +/-0.2, would profile of a line (surface) callout be totally illegal? Since the location of profile tolerance zone is not tied with theoretical perfect distance of top surface from datum A and can float within dimensional tolerance, would you say profile control couldn't be used in such case?

It is just my idea to keep the discussion alive...

 

[ptruitt]

Before GD&T, unilateral or unequal bilateral tolerancing frequently caused tolerance stack-up errors. Also, in many/most cases, suppliers would just calculate where the boundaries of the unilateral or unequal bilateral tolerance zones were in order to maximize Cpk and minimize risk. These days, there is the added risk that CAD models will not be at the midpoint of the tolerance zones and steel may get cut improperly per CNC data derived from 3D-CAD rather than drawing annotations. Whether using plus/minus tolerancing or GD&T, it is a good idea to keep everything equal bilateral, if possible, imho. This has interesting implications when specifying hole sizes with position tolerances plus bonus tolerances.

Peter Truitt
Minnesota

 

[Belanger]

Pmarc, I think that figure is still OK, because the profile is meant to control form and orientation. And since it's a flat surface, the "true profile" is a flat plane with a basic dimension of zero. The height of the part is irrelevant. Even with the 50 +2/+1 tolerance it would be OK because the basic dimension of zero (form) hasn't been affected.

I thought you were going to bring up Figs. 8-17 and 18. I think it was Evan who always disliked those figures, and I kind of agree -- a profile tolerance must always be applied to a "true profile," and the GD&T on those cones is not applied to a true profile as defined in paragraph 8.2. Instead, they show a toleranced diameter! Sorry to digress.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[pmarc]

J-P,

I was just trying to somehow satisfy OP's question by bringing up a situation when profile tolerance zone can actually lie outside nominal dimension. If we are in agreement that 50 +2/+1 dim. together with profile (of a line or a surfce) callout works fine, we are having a case when profile tolerance zone is completely outside nominal dimension 50.

 

[Belanger]

I see what you mean.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[dingy2]

pmarc:

The profile of a line tolerance in Fig.8 -27 is 0.07 and is inside your size tolerance of 50 +2-1. This example is an exception rather than the norm for the use of profile tolerance. You have a 3 size range while the profile has a 0.07. In this case, the feature must meet both requirements and certainly is not illegal.

In most situations, your 50 dimension would be basic with the profile of a line tolerance of 0.07 would default to a bi-lateral tolerance so nothing can be above 50.035 nor below 49.965.

Dave D.

http://www.qmsi.ca

 

[pmarc]

Dave,

I was thinking of 50 +2/+1 dimension not 50 +2/-1, so the tolerance range is 1 not 3 and lies completely outside the nominal value.

I fully agree with you that fig. 8-27 is rather exception than the norm, but like I said, I was just trying to find an example that could prove that profile tolerance zone can lie outside nominal shape of a toleranced feature. If we assume that plus/plus tolerancing is acceptable together with profile callout, we will be having such case.

 

[prabhakardesign]

Thank you very much, for providing the valuable suggestions.

I conclude that (as of now), it is not possible to use Profile Tolerance for which the True profile dimn is outside the tolerance zone.

Profile tolerance can be unidirectional when True profile lies in upper or lower limit of the Tolerance zone.

Please let me know, if any examples are there for Unidierctional profile as above case.

Thank you,
Prabhakar
Germany

 

[dingy2]

prabhakardesign - You are partially correct in your assessment of profile tolerances.

You are correct that a profile tolerance cannot be outside the tolerance zone of the feature if the linear tolerance was large and the profile tolerance quite small in comparison. This situation is quite rare.

In most cases, the feature is shown with a basic dimension reflecting its true profile (theoretical) and the profile of a surface (or line) is about the true profile. It defaults to a bi-lateral tolerance but can be unilateral depending on how it is shown.

The ASME Y14.5M-94 reflects phantom lines on either the outside or inside of the object line indicating a unilateral tolerance while 2009 version has a value in the feature control frame before the U (circle) and another value after it. The first value is the tolerance value on the minus side of true profile while the value after the U (circled) is on the plus side.

Inside a large linear tolerance, the smaller profile tolerance is range of the profile on the surface or line and can be located anywhere inside the upper or lower specification limits as shown on page 179, fig. 8-27. So this is the unidirectional that you were looking for.


Dave D.

http://www.qmsi.ca

 

[DeanD3W]

If using the "circled U" modifier, the value to the left of the modifier is the total tolerance zone thickness, not the amount of tolerance in the minus material direction. The value to the right of the modifier was described above correctly as being the amount of tolerance in the plus material direction (the amount outside the true profile).

I don't find this modifier what I would call intuitive, but that is the way it works... |Total Range of Tolerance (U) Amount outside (in the "plus material" direction) the true profile|.

Dean

http://www.d3w-engineering.com

 

[dingy2]

Dean:

I stand corrected on the U modifier. You are correct that the value in front of the U is the total tolerance while value after the U modifier is the tolerance on the plus side.

Dave D.

http://www.qmsi.ca