【转帖】3d dimensioning

yang686526

3d dimensioning?
hi all,
i keep hearing about the new ansi y gd&t standards through which we can (fully)dimension the cad 3d model itself without actually having a drawing for that model [i may be wrong!]. could someone throw more light on this and tell me in brief how this new gd & t std. is different/an improvement over the existing one?
thanks,
jaya
eng-tips forums is member supported.
  asme y14.41 does not replace asme y14.5, it supplements it.  all of the dimensioning and tolerancing rules are still governed by y14.5.  an exception is the addition of a modifier to profile tolerancing (i was told that this was because y14.5 was not at a stage for a new revision as of yet).
  y14.41 spells out acceptable practices for the dimensioning and tolerancing of solid models in 3d space.  drawings may be omitted, but are still allowed.
  it will probably be a while before this standard is used broadly, as most of the solid modeling software out there has yet to support some of the requirements (such as picking on a geometric control block callout and having the related datums highlight).
  it can be a vast improvement over drawings in helping the understanding of the relationships between features and their control tolerances.
  a drawback is that to be of the most use, all users of the information need to be running the same software, at least until the different cad packages can interpret the information in the same manner.
hi ewh,
thanks for the concise summary- i heard more about this in a recently concluded pro/e users meet and it seems ptc has implemented some of this new std in wf 2.0.but as you rightly said, all users incl shop floor personnel would need to run the same s/w until a common ground is found.
regards,
jaya
jaya,
  when it does come into more wide use, more discipline is going to be needed by the cad operator.  we have one customer who is already using many of the concepts (we both use nx), and when you open the file, it looks like a rats nest.  it takes some time to sort out what is what.  fortunately, they included several thick standards on how to interpret their part files.  this is the first project that i have worked on that lacked drawings of any kind.
  for my part, i look forward to the day when we can understand each others part files and say goodbye to drawings.
ewh,
i've heard of a company (bss) that mandates minimal dimensioned drawings along with the native 3d model to machine shops for part creation.  i see a few problems with this direction in technology.  old school machine shops are extremely slow to trust new technology....their reasoning is we have been doing it this way for years.  for example, designing parts in pro/e 2001 and using mastercam to create tool paths. but instead of importing the 3d model redrawing the sections in mastercam.
best regards,
heckler
sr. mechanical engineer
sw2005 sp 2.0 & pro/e 2001
dell precision 370
p4 3.6 ghz, 1gb ram
xp pro sp2.0
nivida quadro fx 1400
      o
  _`\(,_
(_)/ (_)
do you trust your intuition or go with the flow?
for many years now the automotive industry have had minimal dimensions at least on body panels, facias and the like where the complexity of the shapes would make it impossible to dimension.
usually you just get tolerance on holes, primary and secondary location an overall surface dimension and a trim dimension and the contact points for the checking fixture and even these are only on the model not dimensioned as such.
is this really new technology or am i missing something?
unless you are creating dwgs for auto's or aircraft where as they are automated, dwgs should be fully dimensioned for inspection.
chris
sr. mechanical designer, cad
solidworks 05 sp2.0 / pdmworks 05
i don't think that they created y14.41 just for the auto and aerospace industries.  inspection can be done from the model if the proper software and procedures are in place.  the models are to be fully dimensioned (with the exception of complex surfaces, for which inspection will have to be done relative to the model itself); all that will be missing is a drawing.
ewh,
i know it wasn't created just for auto and aero.
also, especially if the dwgs are for military/space, the dwgs need to be fully dim. you can have a model fully dim, but can not always be trusted. not all models can be sent to vendors because of security or other reasons.
y14.41 is a good spec to have and follow, but not everyone knows about it. most companies i have seen have limited dwgs with minimal dim's because they either do not have a drafter or do not know how to do dim's much, or don't care. they rely on the 3d models and that is good enough for them. if the military/space industried are willing to change and go this way, i am for it. but will be a long time to come.
chris
sr. mechanical designer, cad
solidworks 05 sp2.0 / pdmworks 05
ctopher,
  the parts i referred to on 12 apr are part of a security sensitive project for the military.  one key to maintaining sensitive information is to not give your vendors the whole picture, but just enough so that they can produce the parts you need.  it may just be a matter of time before all of the defense industries are able to go totally 3d.
  some of the projects we work on are not secret and don't have to be super-precise.  in these instances, we send out dumb solids to the toolmakers with a purchase req stating our requirements.
   on a related note, eclipse aviation is working with the faa so that the certification process design reviews for it's new jet are being done digitally.  the faa usually requires paper drawings for this.  eclipse still produces reduced dimension drawings for it's vendors.
  i agree that it will probably be quite awhile before we see this standard adopted on a wide basis.
interesting, thanks ewh. i'll look up eclipse aviation.
chris
sr. mechanical designer, cad
solidworks 05 sp2.0 / pdmworks 05