A-c datum alignment

Opinion needed:

Was wondering if it was possible for one of these holes (dat-c-) to give good t.p readings. Since the parts is symmetrical all 3 holes should be used with dat-a- for an alignment (a-c in feature control frame). So it would be possible for a different selected hole to be dat-c- and give out of tolerance true position readings. Correct?

Attached Files

PART (2).pdf

YGOLORTEM over 9 years ago

Where is Datum -A- and Datum -B-? I only see Datum -C- in that picture.
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Shane-o over 9 years ago
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Schlag over 9 years ago

The drawing is defining 1 hole as C. If the hole pattern was C, wouldn't -C- be attached to the Feature Control Frame or the 3x designation ?
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NinjaBadger over 9 years ago

The drawing is defining 1 hole as C. If the hole pattern was C, wouldn't -C- be attached to the Feature Control Frame or the 3x designation ?

I don't think that's what he's asking, as far as I can tell when he picks up the part it rotationally symmetrical, so he can in effect choose any one of the holes to be his datum C hole.

What he's asking (I think) is could the results vary depending on which hole hi picks?

Is that right?
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Obelix over 9 years ago

I can't read this, but if your datum B is a surface and datum A center hole there is no need for B/A/A-C as B/A/C would do the same thing
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NinjaBadger over 9 years ago

I can't read this, but if your datum B is a surface and datum A center hole there is no need for B/A/A-C as B/A/C would do the same thing

+1
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Shane-o over 9 years ago

yes ninja that is what I was asking. so do you think its possible to choose one as datum c and receive good results, and then rotate it and then use the other hole as datum c and then receive bad receive. I only ask because that's the issue I am having. and yes the center hole is dat-a- and yes a plane on the part is dat-b-
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YGOLORTEM over 9 years ago

I could barely make it out....

I can't read this, but if your datum B is a surface and datum A center hole there is no need for B/A/A-C as B/A/C would do the same thing

+2
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NinjaBadger over 9 years ago

yes ninja that is what I was asking. so do you think its possible to choose one as datum c and receive good results, and then rotate it and then use the other hole as datum c and then receive bad receive. I only ask because that's the issue I am having. and yes the center hole is dat-a- and yes a plane on the part is dat-b-

I'm trying to figure that one out and it's making my brain hurt.

I'm thinking it shouldn't be possible really.

How are you dimensioning it? Using FCF or Legacy?
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VinniUSMC over 9 years ago

yes ninja that is what I was asking. so do you think its possible to choose one as datum c and receive good results, and then rotate it and then use the other hole as datum c and then receive bad receive. I only ask because that's the issue I am having. and yes the center hole is dat-a- and yes a plane on the part is dat-b-

If the 3 holes are shifted off-center as a pattern, or if 1 hole is quite differently deviated than the others, I think that it is possible to receive differing results.
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