Datum set-up and referencing
Datum set-up and referencing
(OP)
Say you start with a square plate with 2 holes. The surface of the plate is identified as datum A, 1 hole is datum B and the other hole is datum C. Then lets say datum features B & C are not parallel (horizontal or vertical) to the edge of the plate.
Q: Since datums B & C are both axis, would they be an adequate secondary and tertiary datum reference for position and clocking hole patterns?
Q: If so, the clocking orientation is relative to a theoretical line from one datum axis to another, in this case not parallel to the plates edge?
Q: If so, and you want a hole pattern clocked parallel to the plate edge, a basic angular dimension from the theoretical line between B & C datum axis and the hole pattern is required?
Q: Since datums B & C are both axis, would they be an adequate secondary and tertiary datum reference for position and clocking hole patterns?
Q: If so, the clocking orientation is relative to a theoretical line from one datum axis to another, in this case not parallel to the plates edge?
Q: If so, and you want a hole pattern clocked parallel to the plate edge, a basic angular dimension from the theoretical line between B & C datum axis and the hole pattern is required?
Thanks,
Sean





RE: Datum set-up and referencing
RE: Datum set-up and referencing
Thanks,
Sean
RE: Datum set-up and referencing
Since B is not perpendicular to A it will likely constrain the one remaining rotation as well as the two remaining translations rendering C without any degrees-of-freedom to constrain.
If you want B to only constrain the two translations then you will have to say so. You could do it in a note if dimensioning to ASME pre-2009 or with a modified DRF according to the 2009 Standard.
Paul
RE: Datum set-up and referencing
Paul
RE: Datum set-up and referencing
Datums B & C are perpendicular to datum A. What I mean is, datums B & C, relative to each other, are not parallel to the vertical and horizontal edges of the plate.
Thanks,
Sean
RE: Datum set-up and referencing
Frank