Ours had three segments (much more current drawings) They wanted to know. I've worked on similar looking parts and they were called out similar to that. Other than that you can best-fit to your hearts content. It has to have a defined exact location established by basic dimensions and/or datums. A positional tolerance defines either of the following: There is no true position without some manner of relation to another thing. True Position 14 The easy way to do this in Calypso is to take your primary datum plane and the origin, rotating along the origin to bring one of the -B- datum (A) holes to the correct distance from the axis per the drawing then checking the true position of each -B- hole to the plane / origin / rotated alignment.

The Position of C will be a single axis position, controlling the location of C relative to B and the orientation of C relative to A & B. The one datum constrains all the dof it can (which is two rotational and translation along the other). Position is the location of one or more features of size relative to one another or to one or more datums. The more proper and elegant choice for the designer here would be Perpendicularity rather than Position, but again, the resultant control is the same.įinally the instructions JacobCheverie provided are spot on. Position of the secondary to primary is not prohibited by ASME Y14.5, but the geometric reality is the only thing it controls is the orientation relative to the primary. In most cases, flatness for a plan or cylindricity for a cylinder.įor the secondary datum feature, it is usually possible to control the orientation relative to the primary, and in doing so, one also controls the form of the secondary datum feature.įor the tertiary datum feature it is usually possible to control it's orientation, form, and location relative to the primary and secondary, with the caveat that the location will usually be a single axis control as the tertiary itself establishes the other axis, (as is the case with the plane-hole-slot DRF you describe.) When more than one datum feature is used to establish a single datum. In this case the basic dimension 30 from the center of the large (are those gear teeth) diameter in the middle and the basic dimension 17.3 from the hole labeled 'B'. As they are the foundation of the DRF, the amount of control possible increases as the DRF is constructed.įor the primary datum feature the only control possible is form. Form Error (shown in Fig.3-1): is the variation of the true form of a single. You can calculate the true position with only one datum in the feature control frame - you need the deviation from the basic dimension from that basic dimension's origin. Best practice is to control the datum features to the extent possible.

True position to one datum