【转帖】positional tolerance zones 9square vs. round0

yang686526

positional tolerance zones (square vs. round)
bare w/ me - i am new to gd&t.  thought i had positional tolerance figured out....but nooo....anyway, here is my question:
if i put a diam. symbol in front of my positional tolerance, how does that affect the zone?  if i do not use a dia. symbol, is the zone a square?  thanks for your patience.
jim weed
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james-
in asme y14.5m-1994, para 3.6 states:
"where the specified tolerance value represents the diameter of a cylindrical or spherical zone, the diameter or spherical diameter symbol shall precede the tolerance value.  where the tolerance zone is other than a diameter, identification is unnecessary and the specified tolerance value represents the distance between two parallel straight lines or planes, or the distance between two uniform boundaries, as the specific case may be."
that said, i have found that in many cases where the diameter symbol is absent from a true position control frame, the person who drew it either didn't know or bother to put it there.
that help?
-john
i agree with john.
jim, very good queestion. most newbies would never think of that.
chris
systems analyst, i.s.
solidworks 06 4.1/pdmworks 06
autocad 06
we use the positional tolerance sans dia symbol on all our slotted bushing locations allowing .010 in on direction and .040 in the long direction.
i cant think of another use to eliminate the dia symbol.
cheers
i don't know anything but the people that do.
thundair,
i believe i can supply you with another application for square or rectangular zones.  
suppose you have a rectangular plate of some sort with a pattern of holes, and apply composite positional tolerancint.  it would seem to make sense to allow a rectangular pattern for the pltz.  this would effectively control the edge distance, and give the bonus tolerance.  for the feature relating tol zone use the dia.
comments?
diameter tolerance zones should be placed on features of size that are round only!!!! nothing else.
do not place them on slots or any other feature that is not round.
thundair - if you want a bi-direction tolerance on slots, please have two (2) feature control frames showing direction and the .010 tolerance in one and .040 tolerance in the other one. do not place a diametrical tolerance zone prior to these tolerances. also, place  "boundary" below each feature control frame. this reflects that the "boundary" is the virtual condition size in both directions.
dave d.
thanks everyone - very helpful.
dave, you're quite right on the application.  to address the original question though, in the absence of a tolerance zone shape modifier (spherical-diameter, diameter, or square), you get a tolerance zone parallel to the last datum in the datum reference frame of the fcf.  the square symbol is needed in the fcf if you want to indicate a square tolerance zone.
jim sykes, p.eng, gdtp-s
profile services
cad-documentation-gd&t-product development
dingy2
right-on that is exactly what we have although at detail level i tried to get a dia positional tolerance for the hole...i was shot down and we only dimension assy level.
especially now that we are mbd...
ringman
i would just use a composite tolerance in that application
cheers
i don't know anything but the people that do.
thundair,
i was allowing that composite tolerancing be applied.  the question relates to the pltz and frtz. i see no reason that the pltz could not, and should not, be rectangular.
ringman
i reread your post and in the words of rosana rosana dana
never mind..
you are correct.
cheers
i don't know anything but the people that do.