【转帖】pattern locating tolerance zone

yang686526

pattern locating tolerance zone
why is it that rarely, if ever, a rectangular tolerance zone is used when compound positional tolerancing is required on a drawing?  assuming for the moment that the outline is of a rectangular configuration.  i know of no examples in the y14.5 illustrating this.
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why do you think it is "required"? depends on the design.
can you show a pic of the detail of what you are referring to?
chris
systems analyst, i.s.
solidworks 06 4.1/pdmworks 06
autocad 06
when you say "rectangular tolerance zone" are you refering to what you would get if you used +/- dimensionsing?
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ben loosli
sr is technologist
l-3 communications
looslib,
it would replace the "rectangular zone", as once allowed and described in the standard.  the benefit is that by using the rectangular or square zone for the pattern locating tolerance zone, it would provide the 'bonus tolerance' and more directly establish the minimum edge allowance for the pattern or holes.
(i should have mentioned pattern locating tolerance zone in my initial post, but failed to do so.)  hopefully this will clarify my original question.
ringman,
   are you talking about a tolerance zone for a hole that interfaces with something like a slot?
                         jhg
a pic would help.
chris
systems analyst, i.s.
solidworks 06 4.1/pdmworks 06
autocad 06
not sure how to post a picture.  but will try to describe my intent.  suppose a rectangular plate with a 4 hole rectangular pattern in the plate.  the hole to hole relationship requires, lets say, a .028 dia positional tolerance.  however the pattern of holes may be located to a much looser tolerance, on the order of .o6 dia.  if we elect to use composite tolerancing, why must the pltz or pattern locating tolerance zone be expressed as a diameter?
(no slots or square fasteners involved) :>)
hope this will help to clarify
how can i show an image in a post
try reading
i will try again using a little different approach.
using the example fig. 5.19,in the y14.5 1994, on page 96. relative to the 4 hole pattern in the plate: why does the pattern locating tolerance of 0.8 have to be a dia?  a square zone of 0.8 on a side would provide the 'bonus tolerance'.
ringman,
   i see two possibilities here.
   you could replace the diameter symbol with a square so show a square tolerance zone.  this is not shown anywhere in the standard, but i see no reason why it is not valid.  i also cannot see why you would do it.
   your composite tolerance could look something like the following...
   pos .05 a b
   pos .15 a c
   pos dia .028 a
   datum_a would be your base.  datums_b and_c would be edges.  your tolerance area is rectangular, as opposed to round or square.
   does this make sense?
                                jhg