Tangent Plane

[Belanger]

The ASME Y14.5-2009 standard embellished the explanation for the "tangent plane" modifier a little. The 1994 edition made it sound like it was only for the three orientation symbols, but now in paragraph 6.5 it has an extra note saying that "it may also have applications using other geometric characteristic symbols..."

I'm trying to think of another GD&T symbol that may use the T modifier, and all I can come up with is profile of a surface (and even then it cannot be a contoured surface, but only flat), and maybe total runout on a flat surface. Any other insights?

John-Paul Belanger
Certified Sr. GD&T Professional

http://www.gdtseminars.com

 

[SeasonLee]

Yes, the profile of a surface can be used with the T modifier, but I am not quite sure for total runout on a flat surface.

However, we can apply the T modifier on a parallelism callout, for example : Parallelism|.005 circle T|A The tangent plane contacting the high points of the surface must lie within two parallel planes .005 apart which are parallel to datum plane A.

SeasonLee

 

[Belanger]

Right -- I've seen tangent many times on all three of the orientation tolerances. And I suppose profile with T makes sense, but again, it can only be used on a flat surface. And I'm thinking it really only could be used for coplanar surfaces. (Otherwise, what benefit does it provide?)

If it's used on total runout, it can only be on a surface that's perpendicular to the datum axis, but it won't control form.

Maybe they just put the note in the standard kind of as a CYA for some of these weird situations which may come up...

John-Paul Belanger
Certified Sr. GD&T Professional

http://www.gdtseminars.com

 

[MechNorth]

Season, the application to orientation didn't make sense to me at first because an orientation tolerance zone (wrt a datum that is) covers the high point to the low point on the surface. Then I read the actual section 6.6.1.3 and recognized that the three highest points would establish a tangent plane. Interesting.

Application to form wouldn't make any sense; you want the actual surface, plus it explicitly states in '09 that it doesn't control the form.

Position? Wouldn't that just be the loc'n of the true geometric counterpart anyway?

Runout? You need to contact the actual surface, but then that's what I thought for orientation too. I'm picturing a knobby cylinder where the indicator is only allowed to touch the tangent end ... that would theoretically just be circularity at a non-continuous diameter, wouldn't it? Same thing for a surface perpendicular to the datum axis.

Orientations & profile controls are all that I can see.

Paul, here's a link to a practical use of (T) with a profile of a surface control.

http://www.tec-ease.com/tips/september-06.htm

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[axym]

How about Flatness? ;^)

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[ringman1]

To the best of my recollection, tangent was interpreted as having contact at a single point. Of course, that was years ago in a Geometry class in school. When did it get expanded to 3 points?

 

[axym]

ringman1,

Good to have you back.

The term "tangent" in Y14.5 has a different meaning than it does in geometry. In Y14.5 it means "contacting the high points". So the Y14.5 tangent plane used in orientation tolerances is a perfect plane that contacts the high points of the imperfect actual surface. In general, the unconstrained tangent plane will contact the actual surface at 3 points. See Fig. 6-43 in Y14.5M-1994.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[MechNorth]

I'll not be taking that hook, Evan. Tks!

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[ringman1]

Evan,

Got to ask, but what is an unrestrained tangent plane?