Datum Callout
Datum Callout
(OP)
A throttle shaft with two tap holes for mounting the throttle plate.
Let put the shaft horizontally (left to right), draftman draws a vertical line between & midpoint of these two tap holes and calls it a datum A. He then make a basic dimension from this datum A (this vertical line) to one tap hole, a basic dimension from this tap hole to the other tap hole. He wants to control one end of the shaft so he makes a basic dimension from datum A above to the end of the shaft.
The question is: IS he correct to callout datum A ( a line established between & midpoint of these two tap holes)?
The Inspector will use two pins (each for each holes) & locates the center point between two pins for his datum.
Please advise. Thanks
Let put the shaft horizontally (left to right), draftman draws a vertical line between & midpoint of these two tap holes and calls it a datum A. He then make a basic dimension from this datum A (this vertical line) to one tap hole, a basic dimension from this tap hole to the other tap hole. He wants to control one end of the shaft so he makes a basic dimension from datum A above to the end of the shaft.
The question is: IS he correct to callout datum A ( a line established between & midpoint of these two tap holes)?
The Inspector will use two pins (each for each holes) & locates the center point between two pins for his datum.
Please advise. Thanks





RE: Datum Callout
A datum must be a feature you can locate from. This means it either is an edge, or a feature of size.
Ask your drafter to propose a fixture that will pick up his datum.
RE: Datum Callout
"Wildfires are dangerous, hard to control, and economically catastrophic."
Ben Loosli
RE: Datum Callout
The coordinate system reference for inspection purposes would then be central to the 2X pattern on the axis of the rod ends for any fcf's that referenced the rod-ends primary and the 2X threaded holes secondary.
It would be logical for the basics to be referenced to that origin... the datum identifiers however must be placed on the features that establish these centerlines not on the lines themselves.
Paul
RE: Datum Callout
Looslib. That is exactly what I have in mind to tell him. But I am not sure his way is correct. Thanks.
RE: Datum Callout
RE: Datum Callout
Frank
RE: Datum Callout
Using patterns for datums can be problematic as the topic isn't covered in much detail in the standard. However, for 2 holes it's simple enough.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?