"CAD is Master" note 1

[BrownsFanGodHelpMe]

Hello,
I deal with thin metal stampings and have a customer that is insisting that I have our parts 3D laser scanned because he interprets the note "CAD is master" on the print to mean; Whatever dimension is not listed on the print must be checked to the Math Model.
I have always interpreted "CAD is master" to mean; if there is a discrepancy between the Model and the Print, the Model supersedes the Print.
We do a point cloud CMM layout at PPAP and annuals, and we check parts to an attribute gauge. We feel this is more than adequate to check thin metal stampings to the print and/or CAD.
Also since our materials are thin we check the parts in a constrained state. I don't even know how you could scan parts on a fixture.

Your thoughts?

 

[KENAT]

Saying CAD is master is no help since both 3D model and 2D print are CAD so I see plenty of opportunity for misunderstanding from your note.

If you have missing dimensions on your print, and reference the model, then your customer has a point about wanting the part verified against the model.

However, dictating the process is questionable - especially if as you say the proposed process may not be appropriate.

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[CheckerHater]

Agree with KENAT: in a perfect world your drawing (and model for that matter) represents fit form and function and NOT the process.

In the real world, anything you place on your drawing may and will bu used against you like charging extra for every FCF.

 

[drawoh]

BrownsFanGodHelpMe,

We are implemented Model Based Definition (MBD) here. I object to terms like "limited dimension drawing" and "CAD is Master" because they have no meaning. I have updated our title blocks to state that if the feature is not dimensioned, the dimension is whatever is on the 3D[ ]CAD model.

In a narrow technical sense, you need to prove that your part meetings their drawing and model. How accurate is a laser scanner compared to a CMM?

On the other hand, this is not really a problem. If your customer wants parts laser scanned, laser scan them, and adjust your prices accordingly. Warning them that you are about to do this is possibly an even better idea.

--
JHG

 

[3DDave]

It seems like a contract that fails to make clear what is satisfactory evidence of meeting the contract requirements.

"CAD is Master" tells me that the CAD model describes the ideal geometry from which certain deviations are tolerated. If the part requires constraint to be inspected, those constraints should be on the drawing or somehow represented in the model.

If you can perform a CMM check with the part in the inspection fixture, there's no reason using a laser is any different.

 

[Tunalover]

I would reserve the model-as-master approach only for parts that are very complex and impossible to draft on a few drawing sheets. Stamped parts are usually not-so-complex so I would lean towards drafting them complete with all dimensions and tolerances.


Tunalover

 

[ctopher]

I personally have never seen "CAD is Master". I have only seen "CAD Drawing, NO MANUAL CHANGES" or something similar.
It seems to me that using "CAD is Master", there is no point of having a dimensional drawing.

In today's over-sensitive world, it would seem "CAD is Master" would be not PC. ;-)

Chris, CSWA
SolidWorks 14
SolidWorks Legion

 

[MintJulep]

because he interprets the note

It's your drawing. It's your note. You define the interpretation, not him.

Hopefully you have the meaning actually documented somewhere in your company standards.

 

[ewh]

"CAD" originally was an acronym for Computer Aided DRAFTING and when it originated the model (if there was one) was not of the same detail or complexity of those we have today. To state "CAD is master" is meaningless, unless there is another board drawing of the same part still floating about.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[CheckerHater]

It's "CAD DATA IS MASTER":

http://www.allrite.com/533eed01e0ac6-AA-00080737_A_TUBE_SOR_LH.pdf

Not to mention that "D" may be interpreted as "design".

Your "cad data" represent theoretically exact (basic) sizes and shapes. You still need to apply GD&T to something which may be "flat" 2D drawing.

 

[ewh]

OP referred "CAD IS MASTER".
Both drawing and model contain data.
Board drawings are also "designs".
I stand by my statement that "CAD(D) DATA IS MASTER" is meaningless without further definition as to which data is indeed the master.
But then, in my experience I have only seen similar statements declaring that "CAD MODEL TAKES PRECEDENCE OVER DRAWING."


“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[KENAT]

Here's a couple of notes we use when going MBD. In addition either the second note is edited, or an additional note added. with default surface profile tolerance.

1. DIGITAL PRODUCT DEFINITION PREPARED IN ACCORDANCE WITH ASME Y 14.41-2003.
2. THIS DRAWING SHALL BE USED WITH MODEL (INSERT PART NUMBER) (REVISION PER THIS DRAWING) FOR COMPLETE PRODUCT DEFINITION. MODEL GEOMETRY IS BASIC.

Posting guidelines faq731-376

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

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

 

[BrownsFanGodHelpMe]

Thanks for the replies, I should have clarified that it stated Cad Model is master not just CAD