The datum simulator is the bottom of the sink. The primary datum feature is the bottom of the pan. (Assumptions are that the pan is round, the sink is rectangular, and the pan can sit flat on the bottom of the sink.) Take a frying pan and place it in the kitchen sink. Datum feature identifiers can be placed in multiple ways to identify datum features.ĭatum theory is observable at home. The datums establish the coordinate system and origin for location and orientation.Īnd, as stated previously, the datum isn’t established until the datum feature meets the datum simulator, whether the simulator is a machine table, fence, or backgauge, or three hits (for a plane) from a coordinate measuring machine.įIGURE 1. And the datum is the “true geometric counterpart” of the datum feature. So, the datum isn’t on the part that’s the datum feature. A datum is the origin from which the location or geometric characteristics of features of a part are established.” So, what’s the relationship among datums, datum features, and datum simulators?Īccording to Y14.5, a datum is “a theoretically exact point, axis, or plane derived from the true geometric counterpart of a specified datum feature. The datums used in CAD should remain distinct from GD&T datum features. Company standards, or the enforcement of best practices, become important. This is a matter of a best practice enabled, but not required, by Y14.5. Doing so, however, will leave off the drawing the useful and potentially cost-saving information of how the part actually locates in assembly (see Figure 2C). In most cases, leaving the CAD datums as GD&T datums would still be compliant with Y14.5 (see Figure 2B). The designer is the first person who knows this, and it might be very useful information to the fabricator, the assembler, and the inspector, both before and after assembly. What’s missing is that this bracket is located in its next assembly by the small hole and the slot. In geometric dimensioning and tolerancing (GD&T), a datum is established when a datum feature meets a datum simulator.Īs an example, to design the bracket in Figure 2A, the designer likely would sketch the perimeter on an arbitrary plane and use the edges as references or “implied datums” to locate the holes and slot as quickly as possible-hasty drafting. It is stuck on the drawing or model representation of an actual part feature used to establish a datum. The symbol used in ASME Y14.5 to designate a datum feature is often referred to as a plunger or a suction cup (see Figure 1). This episode begins to explain datum features, datum simulators, and datums. Editor’s Note: The previous episode of the GD&T Connection was about capturing the designer’s purest intent using basic dimensions and how that relates to plus-or-minus dimensioning methods.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |