Rotating datum feature to align to axis
Rotating datum feature to align to axis
(OP)
There is a hole labeled as 3rd datum |C| feature located in 1st quadrant @60degree from X axis.
The question is: does it matter if you rotate to align with Y instead of X axis for inspecting? Like if you rotate to align Y axis then it's 30deg. or 60deg to the X axis?
The question is: does it matter if you rotate to align with Y instead of X axis for inspecting? Like if you rotate to align Y axis then it's 30deg. or 60deg to the X axis?





RE: Rotating datum feature to align to axis
In other words, the 60 degrees is not of direct importance to the holes themselves. (However, it would help to see the rest of the drawing to explain the full effect.)
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Rotating datum feature to align to axis
RE: Rotating datum feature to align to axis
What numbers will you report?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Rotating datum feature to align to axis
E. Morel
M.E.
RE: Rotating datum feature to align to axis
Thanks for your guys tips.
RE: Rotating datum feature to align to axis
Paul
RE: Rotating datum feature to align to axis
The angle should be 56.31 degrees rather than 60 among other things for that detail to work ...
Paul
RE: Rotating datum feature to align to axis
The new hole is tolerance strictly from A, B, C. That's it.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Rotating datum feature to align to axis
Paul
RE: Rotating datum feature to align to axis
Check out my attached sketch. Notice that the holes are in the exact same location as the other pictures posted in this thread! Thus, the position tolerance that the OP gave in his second upload has been fully satisfied. I simply cranked the outside shape to a different rotation, but that was never part of the given tolerance scheme. Therefore, the 60º was -- from the very start of the discussion -- meaningless to the question being asked.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Rotating datum feature to align to axis
I already said it before - datum is no more no less than reference point of you measurement. If you don't specify what exactly are you trying to measure, the question "check my datums" is meaningless.
It's like having dimension with only one reference point, leaving the other end dangling. Is it correct dimension? Who knows?
We agreed that set up should include flat surface for datum A. A and B will leave one rotational degree of freedom, so we add feature C. Now, to create rectangular coordinate system we may draw our axis / plane directly thru C, or at the angle. It all depends on the rest of the part and what exactly are we trying the measure. The typical example will be Fig. 4-7 (2009) - angled datum feature used to establish rectangular coordinate system
So let me say it again in different words - you cannot check the "correctness" of datums ripped out of context.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Rotating datum feature to align to axis
Set up XY plane on A. Set Origin location on B. Align X or Y with C. Doesn't matter which. The nice thing about this is the Y or X value of C will be dead zero - confirming that alignment - but the nominals for everything else will be rotated and not match the print dimensions.
So from this point you are free to rotate the coordinate system -60 degrees from the actual (not theoretical) location of C. You're doing it right if the coordinates of the actual C fall on a line between the origin and theoretical C. I always check this when reading the CMM report.
Hope this helps,
David
RE: Rotating datum feature to align to axis
Thanks
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