huangyhg

hole pattern
all,
i was reviewing a drawing and came across a pattern callout as shown in my attached example. is this right? i have not seen it done to this format prior to today that i can recall.
v/r
nathan
cad technician/iso director
compass systems, inc. (
no, as far as i'm aware assuming asme y14.5m this is not legal.
they are defining both datums twice.
i guess the intent is to indicate that the hole pattern is centered in the part but this isn't how to go about it.
kenat,
kenat,
thanks. i was sure it wasen't. what section of the asme would call this out? the part being created, must have the holes centered on the plate.
v/r
nathan
cad technician/iso director
3.3.2 of the 94 version kind of addresses not having multiple datums with the same letter.
as to 'implied centering' or symmetry. this is an area of some debate. look at figure 5-4 for an example in the standard. however, this example isn't explicitly demonstrating 'implied centering' so some people doubt it's applicability to the question.
to my mind, if it's obvious the featurs are centered, and the tolerance fcf reference appropriate datums you don't need centering dimensions or similar, they just clutter the drawing.

kenat,
kenat,
this is what i beleve it should look like. comments?
v/r
nathan
cad technician/iso director
i meant to reference
this revision is still incorrect. the symmetry feature control frames just don't make any sense at all.
take the symmetry fcfs out of the design and then you would have the face as datum a, overall width as datum b (would end up the centre line of the width) and overall length as datum c (again, the centre line of the length). the positional feature control frame is now correct as long as there is a tolerance on the hole size.
hope this helps.
dave d.
don't datums b and c need a condition modifier in the fcf? due to datum shift.
jlang17, that would have to be decided based on function. you don't 'have' to have the modifier.
kenat,
besides all problems highlighted by kenat and dave, here is another mistake on the re-post:
material modifier is not allowed on symmetry callout.
seasonlee

seasonlee:
you are correct about the modifier not allowed on symmetry but the symmetry fcf is all wrong in this application so it should be deleted.
dave d.

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