Profile of a Surface Question

[bradacc]

Good morning everyone. I was wondering how you could interpret this situation:
A box with a profile of a surface of .010" on the top surface, and a second profile of a surface callout of .020" on the bottom surface.
What controls the thickness? And what would the tolerance be?

Thank you in advance for any and all replies!

 

[powerhound]

Is there no dimension to tell you how thick the part should be? What about a note? Without one of those, there is no way of determining the thickness. Have I just misunderstood you question?

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[bradacc]

Correct, no thickness callout, no datum reference on the profile of a surface callouts. Inspector says solid model controls thickness using .010" surface as a datum. I didn't think that was the case so I wanted popular opinion on the subject.

 

[CheckerHater]

First things first.
Solid model has to be properly documented.
There should be note somewhere in the model or on accompanying drawing, saying if part was modeled at MMC, LMC, basic, etc.
This way you know what dimensions you derive from the model actually are.
That will be the start.

 

[powerhound]

Sorry about the late response. What CH said is correct. Obtaining dimensions from the solid model is acceptable as long as there is documentation saying that.

I don't know what your specific role is but if you are programming the CNC and/or machining it yourself, this is information that you also need to know, not just the inspector.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[CheckerHater]

Is your inspector the only person who can see GD&T in solid model or the other people can see it too?
It is possible to apply GD&T directly to the model, but everyone should see it when opening file with proper software.

 

[axym]

bradacc,

If there are no datum references in the Profile callouts, then they do not control the thickness. The two callouts would control each surface individually.

I'm not sure where your inspector is getting the idea that the model controls the thickness. The .010" surface being a datum sounds even more incorrect. It's fine to use the model to extract theoretically exact dimensions, but the model itself does not impose anything with tolerances or datums.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[pmarc]

Evan,
One question:
Assuming, just for fun, that in OP's case there is a basic dimension between top and bottom surface of the box, will the two profile callouts without any datum feature references be controlling thickness, or in other words a distance between two planes of the box?

 

[CheckerHater]

I know you didn’t ask me, but just the idea.
I think it gives some understanding of where part material should and shouldn’t be…

 

[pmarc]

CH,
Your answers are always welcome. So if I understand your graphic correctly, you are saying that the profile callouts in conjuction with a basic linear dimension do control distance between two surfaces. Am I right?

 

[CheckerHater]

It's not a size, for sure, but I guess you can call it a "distance"

 

[bradacc]

Thank you everyone for your responses!
1) CH, there is no GD&T in the model, just the part itself.

 

[bradacc]

Here's the print I am going off of.

 

[powerhound]

The drawing is not compliant to any GD&T standard. The original question was only about the surface profile of the top and bottom surfaces. There should be questions about every other feature as well.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[bradacc]

Agreed powerhound, however the debate I was concerned with was whether or not the print + solid model could control the thickness of the part. And if so, to what extent.

 

[powerhound]

If there is a note or something associated with the drawing that states that dimensions queried from the solid model are considered "basic" AND there is a GD&T standard--whether ISO or ASME--invoked, then the answer to your question is yes. If there is no such note and someone is just assuming that the dimensions are considered basic then it's not so certain. If we know that the tolerance zones are equally disposed about each surface then that will create a certain size range, if the tolerance zones are not equally disposed about the true profile, that will create a different size range. This is something that is not clear on the drawing. One can probably make an assumption and may even assume correctly but it's not clear from the drawing.

This response does not apply to the positional callouts.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II