Relax tolerance on all around profile 1

[greenimi]

A pentagon shape is controlled by .005 al around profile (no datum). The mating part is a similar shape part. The product engineer is insisting to add another callout to lessen the tolerance on two sides of the pentagon. In other words, from 5 sides, three of them to be in .005 and the other two in .010 AND still use all around profile. How can I legally, do that?


I realize that I’m speaking somewhat theoretically, but I would like to know what options/tools Y14.5 can offers.


I was thinking to use in between profile (name the corners A, B, C, D and E and use profile between A and B, and another
profile between B and C, etc), but in this case can I use all around profile (for assemble-ability with the mating part)?


Thank you

 

[CheckerHater]

Make [.300] toleranced dimension.

 

[greenimi]

And if I am doing that (.300 toleranced dimension) woundn't be in conflict with .005 (ALL AROUND)?
My point is: doesn't all around profile require that all the dimensions to be basic?

 

[CheckerHater]

There is HUGE discussion about using both datums and basic dimensions with profile.
I personally believe that you can use anything that works, especially if your profile is actually straight line.
For more insight on varying level of control using profile you can take a look at this newsletter:

http://www.mechsigma.com/newsletters/2005_07_Newsletter.pdf

Disclaimer: I don’t work there.

 

[pmarc]

The idea with profile BETWEEN concept looks fine to me - however without profile ALL AROUND then.

But that brings up another question:
Can we treat datumless profile requirements defined for each segment using BETWEEN concept as simultaneous requirement then? With ALL AROUND we could for sure. With BETWEEN - I am not so sure, and that is why I would recommend placing SIM REQT notation under each profile FCF to avoid confusion.

Of course, the problem exist only if we assume that profile callouts with no datum feature references are applied (this may be a case when whole contour is used as primary datum feature). If, however, the contour is oriented/located relative to any datum(s) and the BETWEEN profile callouts reference to this datum(s), simultaneous requirement will be there.

As for .300 dimension being directly toleranced (and not related to any datums):
If other sides of the pentagon are controlled by profile tolerances with no datum feature references, any angular relationship between .300 width and the other sides of the pentagon will not be controlled at all. Keep in mind that directly toleranced dimension is not verified relative to anything. In other words the .300 width inclined at let's say 45 degrees to upper face of the pentagon will meet the print without any problems.

 

[fsincox]

If it is not "all around", then, why say it is? Two profile callouts will do it, too.
Frank

 

[axym]

Hi All,

Pmarc brings up some subtle but significant issues, and I agree with everything he said. The different "datumless profile" FCF's will not have simultaneous requirements by default. The features grouped by each between symbol will be simultaneous with each other, but there will not be a simultaneous requrement between the groups unless the SIM REQT annotion is used.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[CheckerHater]

Just to make it clear: when I suggested making .300 toleranced dimension, I meant to keep all-around profile requirement.

 

[greenimi]

Is it legal to combine ± toleranced dimension with ALL AROUND profile?
CH,
The newsletter you indicated, shows combining ± toleranced dimensions with profile, but not with all around profile.

 

[CheckerHater]

I really don’t see the difference.
In the newsletter profile is applied to smooth curve.
In your example all-around symbol allows your profile definition to “go around the corner”. Imagine that your example didn’t have all-around symbol, but had rounded corners. The symbology just clarifies where to stop (or not to stop).
What’s important is the idea that tolerance zone is allowed to “float”, so your dim tolerance adds to the value of profile.
Ask yourself: what makes you more uncomfortable – the ideas in the newsletter, or demand of your product engineer? After all it is definitely legal to drop all-around requirement and tolerance the part completely different way.

 

[pmarc]

I think it will not be a surprise if I say that I see more disandvantages than advantages of having .300 directly toleranced and profile all around at the same time.

Not to mention that geometrically this will never be equivalent to having .300 width basic and two looser profile of surface tolerances applied to both surfaces of the width.

 

[CheckerHater]

I am not defending my idea as the “best solution”.
The way I understood it, OP was not about finding simple “textbook” solution, but rather some weird way to make profile tolerance .005 and .010 at the same time to satisfy other engineers requirement.
I came up with weird suggestion (which I think still has some merit).
We can try to discuss it further or simply say “No, one cannot have profile tolerance .005 all-around and also .010 in some places all at the same time”.

 

[fsincox]

Ch,
Thank you for posting that sheet, very interesting.
Frank

 

[pmarc]

I have 2 questions regarding the newsletter attached by CH:
1. Which paragraph/figure of Y14.5M-1994 standard (I assume it is '94 edition, since the newsletter is from 2005) says that directly toleranced dimensions have power to locate geometrical tolerance zones as suggested by the text associated with figure 2?
2. Which paragraph/figure of Y14.5M-1994 states that presented way of attaching profile FCF with part's outline (all figures) applies to whole contour of the part?

 

[Belanger]

Pmarc, I agree with you on one of those points. But first, what is your issue with Figure 2's text? I don't see anything wrong with their Figure 2 as far as the "directly toleranced dimensions" goes. They are saying that those D.T.D.s only orient the zone, but not locate it. That sounds right to me.

I agree with your second point: a purist would say that the profile tolerance in all those figures only applies to the straight portion (the upper segment of the hourglass shape). As soon as we hit the radius, it's technically a different "feature." However, many would say that the basic dimensions for the radii leave us no choice but to think that the profile continues for the entire hourglass.

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

 

[pmarc]

"Since we used a "plus/minus" dimension (7.24±.05) to locate the profiled surface to datum A, the profile tolerance does not control location."

 

[Belanger]

The profiled surface is being located. The profile tolerance is not being located.
(In other words, the tolerance zone goes to wherever the surface happens to be.)

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

 

[pmarc]

That is even worse, unless you see nothing wrong in applying directly toleranced dimension to the center of radius.

 

[CheckerHater]

ASME Y14.5-1994 has absolutely no problem with using directly toleranced dimensions to specify profile.
From Para.6.5: “If the drawing specifies individual tolerances for the elements or points of a profile, these elements or points must be individually verified.”
If you have tolerance, you check it – that’s the only concern.
And later: “the true profile may be defined by basic radii…dimensions…, etc., etc., etc.
No “must”, no “shall”, not even “should”.

 

[fsincox]

So you guys are OK with profile specified as stated? Back when I mentioned doing something like this to replace runout it seemed to cause a stir?
CH,
Who is this expert anyway, I notice no name is mentioned?
Frank