【转帖】basic dimension versus tolerance dimension

yang686526

basic dimension versus tolerance dimension
hello,
i am really confused by gd&t. sometimes i am told to use basic dimension to dimension an aligning hole, sometimes i am told to use tolerance limit +.005, -.000 for mating part 1, and +.000, -.005 for mating part 2.
my question is when to use basic dimension and when to use limit tolerancing?
thank you
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use basic dimensions to locate the holes, limit tolerancing to size the holes.
use basic dimensioning to locate features, use tolerances on the size of features.
"wildfires are dangerous, hard to control, and economically catastrophic."
ben loosli
sr is technologist
l-3 communications
if you're confused with gd&t then may i suggest that you get some training before attempting to use it.  at the very minimum do you have the specification that govens gd&t?  gd&t is a language and can create costly mistakes if not used correctly.
best regards,
heckler
sr. mechanical engineer
sw2005 sp 5.0 & pro/e 2001
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never argue with an idiot. they'll bring you down to their level and beat you with experience every time.
the other confusion is that people forget about the 'd'.  there is a science to dimensioning and not just adding a basic dimension with a positional locating tolerance.  sometimes, a dimensional tolerance limit is all that is needed to satisfy the function of the part, other times more control is needed.
other than taking a gd&t class, performing a tolerance stack-up analysis on your assembly will probably answer your question.
--scott
thank you all for your input.
i took a basic cad course in my senior year of college, and unfortunately it didn't focus on gd&t.
i do need some training, and your advice about the best website to learn about gd&t will be greatly appreciated.
thank you
lokho
lokho, try
thanks shaun,
that is some really useful website.
i understand the convenience of online training, but for something like gd&t, only a classroom experience works, in my recent experience anyway.
lokho,
here is a website for good solid gd&t training:
tec-ease provides in-house and seminar training where there is interest.  excellent trainers (don, brett and frank) and mentoring style.  they worked with me as i studied for my gdtp-s exam.  i found their materials and methodologies much easier to follow and more informative/applicable than the neumann method that so many trainers follow verbatim.