![]() ![]() This doesn't mean that an axis, center plane or center point cannot be a datum. If we're using a CMM and we have not made any physical datum feature simulators then our job is to model the concept of the datum feature simulators so we get a datum reference frame that is oriented and located as closely as possible to that which a physical datum feature simulator set would provide.Ī datum feature label may not be applied to an axis, center plane, or center point on a drawing because none of those things are datum features. As J-P said, datums are found within datum feature simulators, not within datum features. Those labels are absolutely not datum labels, many people may say the terms that way that is not at all what the standard says.ĭatums are theoretical and can never really be "found" whether they're in the center of a feature or not. Datum Features are identified with datum feature labels. I'm feeling the need to support J-P here. Lorono's SolidWorks Resources & SolidWorks Legionįollow me on Twitter RE: Centerlines as Datums ozzy1 (Mechanical) The center does not magically exist by its own right. Either way, it's the engage of the real world surfaces that creates the center. I believe Belanger's comment refers to the fact that you can use the center of a feature as your datum, but that center is the result of clamping the feature (retangular) or pinning it (hole). A datum is always associated with some real world feature. So a centerline cannot be a datum.To perhaps clarify Belanger's other comment "To sum up, a datum can indeed be a centerline, but it is never to be labeled as such on a print." This is actually not 100% true. How do you constrain your part with an empty point in space or from inside the material? You cannot. The way to look at datums is that they are constraints on your part. (Don't create new features just to be datums yes, I've seen someone try to pull that stunt before.) As Belanger noted, a centerline is imaginary and therefore cannot be used as a basis for a datum. Simply, a datum must be associated with some real world feature, and that feature should have something to do with the design intent. RE: Centerlines as Datums Belanger (Automotive) 22 Feb 11 11:21 (Or if you're looking at the older 1994 edition, it's paragraphs 1.3.3, 1.3.4, and 3.3.2.) See the ASME Y14.5 standard paragraphs 1.3.13 through 1.3.16 and then especially 3.3.2. But if you have the correct definitions in mind, it's OK to say verbally that a centerline is a datum. So I imagine that is what your colleagues are referring to and in that case they're right. This is something we can touch, and this is what should be tagged with the datum letter on the actual print. The other term is "datum feature," which is the actual physical feature that is grabbed in order to derive that perfect plane, axis. There can also be problems with clarity: sometimes several features share the same centerline! (See the attached graphic for the good and bad examples.) However, on a drawing that centerline should never be identified with the datum feature symbol (the triangle with the letter) because a centerline is imaginary, and we can't touch it. ![]() So on that count, yes a centerline can be a datum. A datum is a perfect plane, axis, or point. ![]() Well, first we need to distinguish the terms. ![]()
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