Position tolerance of an axis?

[tanner78]

Hello all,

In your opinion can I give a position tolerance of an axis?
I have defined the axis through 3 angles and one point (defined by 3 coordinates x-y-z), since this axis refers to a complex inclined geometry. So the next step would be the definition of the position tolerance on a diameter. Unfortunately I do not have a real diameter due to the complex shape. I can find much more easily an axis.

Thank you!

 

[KENAT]

Does your feature pass the 'caliper test' or more correctly 'Feature of Size':

Feature of Size. One cylindrical or spherical surface, or a set of two opposed elements or opposed parallel surfaces, associated with a size dimension.

Generally tolerances are applied to features, not theoretical axis or planes etc.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Belanger]

Instead of axis, since it's a complicated geometry it might be better to use the "boundary" idea. In GD&T it would still be the position symbol, but the interpretation would be based on the physical boundary of the feature, not its axis.
There's also the option of using profile of a surface, which controls the location (and form) of the physical surface.

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

 

[drawoh]

tanner78,

You can only apply position tolerances to real features (of size). Can you apply profile tolerances to faces?

--
JHG

 

[tanner78]

Yes, I've already applied profile tolerances to the faces.
The overall surface is a mix of splines which lead to a sort of ovoid-shaped tube.
Profile of a surface is surely the best way, but for the measurement a kind of "reference" axis or point is needed to begin with the measurement. That's why I'm trying to use an axis.

I hope I made myself clear. Thank you very much for your replies.

 

[KENAT]

You can still locate the surfaces from the theoretical axis, and have the axis located by basic dimensions tying back to the datums. However, the tolerance is only applied to the surface.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​