Let me try to respond to your questions from your post: RE: What is a "datum line"? lfw618 (Mechanical) 6 May 19 18:21
#Datum in drawing simulator
V-shaped datum feature simulator is required, B1 and Relative to datum targets A1 and A2 with a basic dimensionĪnd shown as datum target lines. In the front view, datum targets B1 and B2 are located Simulator established from two datum target lines. "4.24.5 Establishing a Center Plane From Datum Targetsįigure 4-47 is an example of a V-shaped datum feature So, in my opinion, a clear distinction is made on datum target line versus tangent plane V-shaped. The text goes further and explained the procedure/ drawing indication if V-shaped tangent plane is required. Your "axis" or datum axis is the axis of a datum feature simulator established from the datum feature.ĭatum target lines, as discussed before are good examples, and if 4-47/2009 is considered, then the V-shaped simulator is established from 2 datum target lines.
#Datum in drawing professional
GD&T Professional RE: What is a "datum line"? greenimi (Mechanical) 6 May 19 18:02įor instance the axis of a cylindrical tube is not necessarily "physical", but would be a valid datumĪgain, the datum FEATURES shall be identifiable. You might want to review figure 4-3 in 2009.Ĭertified Sr. However a cylindrical datum feature establishes a perfect datum axis AND always two perpendicular planes interesting at 90 deg on the axis and can be simulated by the center of a machine tool spindle - a line element like an axis.Ī width datum feature - two parallel planes - a keyway for example - establishes a perfect datum center-plane and can be simulated by the center of a machine tool spindle - a line element like an axis. The physical datum features come in contact with the physical simulators to "simulate" the perfect datum.Ī planar datum feature establishes a perfect datum plane and is simulated by a plane in the shop - notice plane, plane, plane - easy to grasp There are physical datum feature simulators in the processing equipment (in the shop) - machine tools, surface plates, etc. There are physical (imperfect) datum features that are on the part. This is greatly simplified for the Standard but: There are datums, which are perfect. I suspect you may be missing some of the subtle differences in the "datum" terminology RE: What is a "datum line"? Belanger (Automotive) 4 May 19 15:55
It seems that mentioning a line related to the datum target concept as a type of datum is much like mentioning a cylinder related to the datum feature concept as a type of datum. Datum targets designate selected portions of datum features, and much like complete datum features, associated with simulators which are used to derive datums further down in the process. I think that datum targets are closely related to the concept of datum features, less so to datums. I have difficulty with the suggestion that the datum line mentioned in the definition of the term datum is the datum target line. Was it reversed back to the older terminology in the new standard? According to Nonmandatory Appendix A in the 2009 standard, the term "true geometric counterpart" was replaced in that revision by "datum feature simulator". I am curious about the change you mentioned in the 2018 definition.
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