Flatness or Profile of a Line?

[ModulusCT]

Hi everyone... Have a look at the attached .jpg please.

Where I work, this is a standard view of a metal housing used to hold a small electrical component that we design and manufacture here.

My question is... Why on Earth would you want to use the profile tolerance on the bottom surface instead of another flatness tolerance? This housing simply sits in a larger housing where it is connected to the outside world. The inner housing is necessary because the electrical component I mentioned need to be hermetically sealed and thermally controlled.

I could even understand using profile of a surface over profile of a line... Am I missing something? Or is 'the way we've always done it' now 'the way we shouldn't do it anymore'?

Thanks,

Mod

 

[KENAT]

Looks a bit odd, is it maybe to allow machine marks in one direction or something?

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

What is Engineering anyway: faq1088-1484

 

[ModulusCT]

Hmm, no I don't think so... I was just talking with a co-worker about this and he said that the thing just sits in a piece of foam.

I'm studying my GD&T, so I don't know everything there is to know about this stuff, but doesn't profile of a line only control that one visible edge of the part when applied to that view?

 

[NomLaser]

This might be of some use to you.

http://tec-ease.com/tips/january-06.htm

They have info on most of the GD&T call-outs and where I go whenever I get confused

 

[ModulusCT]

That site seems to indicate what I had initially supposed... Profile of a line applies to a single line element on a feature. If datums are used, than the line element applies at any particular cross section along the datum.

So the way it is used in the attached image makes no sense.

 

[dingy2]

It really doesn't make sense to me. If one wanted to control a surface for straightness at each element use straightness. Profile of a line could be used to control contours shown with basic dimensions.

Dave D.

http://www.qmsi.ca

 

[powerhound]

I'm in agreement with the others. The profile of a line callout makes no sense whatsoever, especially because it has no datum reference and it doesn't meet the criteria for a legal profile callout with no datum specified.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[ModulusCT]

Thanks everyone... I think I need to read some additional literature on Profile tolerances myself.

 

[MechNorth]

A couple of points to add;
Specifying the profile of a line control on the edge in the view does NOT mean just that one line element; it means each line element on that bottom surface, and each line element is independent of every other line element on that surface. That brings me to point #2; without a datum reference, a profile control (line or surface) controls size (of an enclosed boundary) or form. As a result, it would just mean straightness on that bottom surface.

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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[ModulusCT]

"As a result, it would just mean straightness on that bottom surface."

And thereby independent of the size of the part? So no bonus tolerance?

 

[MechNorth]

No bonus EVER with surface form controls. You can have a bonus if you specify MMC on the straightness control attached to a feature of size, which means that you are controlling the straightness of the derived median line of the FOS.

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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com