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Unread 22-01-2010, 11:35
Andy A. Andy A. is offline
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Re: Contradicting dimensions?

Quote:
Originally Posted by 1075guy View Post
I really fail to see how its even possible to end up with conflicting dimensions on a single drawing, if it was made with any remotely recent CAD program. And really, for the field, I don't understand why there should be conflicting dimensions across different drawings. I'm sure that they draw it up in Inventor or AutoCAD or similar, and then make drawings off of the model. If you use the same model for the source of your drawings, then the dimensions have to add up.
In this case, FIRSTs drawings are right. It was the manual that got it wrong. That sort of cross documentation error is common no matter what you do, and I think it's pretty easy to imagine how that happens. Production drawings often enough aren't made with the benefit of having the entire design modeled in the same program. A lot of drawing sets are a collage of the output of several different programs and individual models. So it is possible to end up with two different dimensions for the same feature, and it happens surprisingly frequently at least before they get proofed (my job for a short while). This is slowly changing as individual programs get better at 'doing it all', but for the foreseeable future things get made with a mix of programs, each good at some aspect of the model.

The biggest problem is just plain ol' over dimensioning. It's a frequent cause of mixing up tolerance levels and ending up with a design that calls for two different levels of tolerance for the same feature. When that happens the dimensions are conflicting. Even though they 'add up' they mean very different things when it comes time to making the part.
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