yang686526

what is the differences between asme y14.5m and iso 1011 ???
as i know, asme y14.5m-1994 is a complete gd&t spec., but iso's gd&t is splited into many iso specifications.
is any boby tell/provide me the whole iso specification no., which related to gd&t? and what are the differences between these two gd&t specifations? or where i can find the answer.
if you were in the uk it would be bs 8888 it's a compendium of all the relevent bs, bs en & bs en iso specs.
not sure specifically on just the iso series.
iso, i am convinced, is in the business of publications for profit. thus unlike asme, they will split up specs into several sub parts and charge you for each one, knowing full well that you will need all of them to get the complete picture. asme does some of this, but nothing like the iso standards. it's like trying to buy a car and having to pay extra for the motor, tranny, wheels, etc.
unless you really need the iso spec, for foreign contracts,forget it and use asme. it has some significant differences anyway, such as interpretation of the envelope principle that y14.5 calls rule #1, ¶ 2.7.1.
there are a lot of "little" differences, and some "big" ones. there's the envelope principle as ron points out, but for me the biggest difference is "theory vs physical". iso lets you hang a datum off of a theoretical item such as an axis, and uses the mean surface as a datum plane, whereas asme hangs the datum on the feature (a hole for example, or a flat surface). i went through some serious discussions about the merits of the two systems, and what i concluded was that asme was physically and mathematically doable with traditional benchtop metrology for the most part, whereas iso required a lot more mathematically derivations to use.
jim sykes, p.eng, gdtp-s
profile services
cad-documentation-gd&t-product development
yes jim, datums to non-measurable axes and centerlines is a biggy. that is one i encounter all the time at this present job. designers think they are helping out machinists by dimensioning that way, not thinking about inspection.
mechnorth,
i was told that iso allows datums on centrelines, but i have not seen an explanation of how they do it. i just assumed that there was some mathematically rigorous way to figure out which round feature the centreline belongs to.
is it that much more complicated?
jhg