Drafting - dimensioning splines/curves

With that sort of data we tend to say 'cad is master' - which is to say, the geometry of the part is defined in the cad file. What you're doing is fair enough to define a bunch of checking dimensions, but dosn't fully describe the geometry of the feature.

The American ASME Y14.5 -1994 Dimensioning and Tolerancing Practice, shows free form curves and sections being dimentioned by a series of uniformly spaced basic dimensions in one direction (x) and basic dimensions (y) that define points on the section curve. This shape is then given a 'profile' tolerance to some principal datums. I believe other standards (ISO, DIN, JIS) describe this in a similar way.

In practice, on aerospace or medical parts, a CAD 'dataset' is called out by part number(file name) and revision as the standard to be inspected against, with several inspection points and/or a profile tolerance of the curve/surface to be reported as needed.

Christopher Gosnell

TRIGON INC. FPD Company

124 Hidden Valley Road McMurray, PA 15317 PH: 724.941.5540 FX: 724.941.8322

----------------------- The fishermen know that the sea is dangerous and the storm terrible, but they have never found these dangers sufficient reasons for remaining ashore.

- Vincent Van Gogh

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Sean Kerslake wrote:

So are you suggesting John that you would not detail the geometry but would simply refer a third party to the CAD file?

Sean

I have a standard note that states that it is a reference drawing, with only tolerances and other information on it, and refer to the accompanying 3d cad file. since i have standard way of identifying it, with the same revision for both drawing and iges etc file, i can refer to what the file will be called, with the revision, using paramaters. I turn this note into a symbol so it , and several versions of it can be added easily to a drawing cheers Craig

ASME Y14.41 defines a Minimum Content Drawing (MMC) which calls out the model as the control document. It's basically an extension of Y14.5 in regards to 3D data.

Anyone out there using this standard yet? I have yet to get a copy.