Projected tangent plane -- What do you think?

[powerhound]

Here's a hand drawn sketch of a question I got a couple of months ago. I've been meaning to post it and just now remembered. Being that the only case of a projected tolerance zone of any kind in the 94 standard is shown as a special case of position I wonder if it's a stretch to use the same concept to project the tolerance zone of the tangent plane of a surface.

See the attached sketch and let me know if you think this is okay to do. If there is an example in the standard that I'm missing, please point me to it. Obviously the sketch is incomplete. I'm just trying to illustrate a point.

Thanks guys,

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2010
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[pmarc]

powerhound,
I think there is nothing in Y14.5 standard that clearly prohibits what you have done.
Just out of curiosity, may I know what is the functional reason behind this? Is it really that only bottom surface of the slot has to be controlled such way? What about the top one?

 

[powerhound]

The edge being controlled guides a saw blade. Kind of like a jigsaw. The blade goes through the slot but when it's in use, the blade rubs against that edge only.

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2010
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[Belanger]

I think it's OK too -- "extension of principles." But be forewarned that it will raise some questions from people. Too many will still see the profile tolerance zone as existing within the body of the part, but your intent is to have the tolerance zone exist entirely outside the part.

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

http://www.gdtseminars.com

 

[pmarc]

powerhound,
One more comment: the legality of FCF is one thing, however (keeping in mind that the sketch is simplified) I would like to see how the slot's height is defined. Is it basic dimension or typical size dimension and what is the tolerance for it? This may complicate the situation a little bit.

 

[powerhound]

There are lots and lots of issues with the full version of this drawing. When the question was originally posed to me, it was hard for me to see past all the peripheral issues and stick to the question asked. In order to stay within the scope of the question I had to ignore all the other stuff and confirm whether or not the FCF was legal. After consulting with others I came to the same conclusion as others on here. It's not expressly prohibited AND it is a valid extension of principle. Thus I told them that it was okay to do but, as JP pointed out, be ready to explain what you mean to anyone who tries to inspect it. Actually, JP, the leader line from the FCF is a little further down the chain line so that it's separation from the actual surface is more apparent.

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2010
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II