【转帖】only a minimum callou

yang686526

only a minimum callout
hi everyone,
this is my first post so go easy please. i've got a part that my mfg engineer wants to dimension as: 3" minimum. is that an acceptable callout? what is trying to be said is that there is no limit on how long it can be, as long as the part is 3" or longer. is this dealt with in asme 14.5? is so where?
thanks in advance for the help!  
i would never dim 3" min. it gives the person making it freedom to make it whatever size they want above 3". always indicate some type of tolerance.
chris
solidworks/pdmworks 08 3.1
autocad 06/08
i agree, you don't want a part 18ft long meeting your specifications.
now if we are talking max, use this frequently for radii that are not critical.  i give the machinist some freedom, if they need a radius, it can be up to this size.  if they don't need it, there can be a sharp corner.
"art without engineering is dreaming; engineering without art is calculating."
i agree with madmango. i have used it for fillets to give machinists' some leeway, tools are not always sharp.
chris
solidworks/pdmworks 08 3.1
autocad 06/08
i use min on full thread depths a lot with the qualifier, do not break through if applicable.  can't immediately think of another situation i use it though.
as mad says, saying 3" min means you'll accept 4" or 5'...
maybe this works for your part but off the top of my head i can't think of a situation that's true in.  
how about 3.5 +- .5 or similar?
kenat, probably the least qualified checker you'll ever meet...
another case: if the source material is known to be a certain size, then i can imagine how a min only callout may be exceptable.  the part would technically be fully defined, though in a round-about way.
in the case of radii, i can imagine that if you are ok'ing a radius but not requiring it, then a max only callout might be acceptable.
in any of the cases listed by me and others here, there is always a limit of some sort in the other direction.  it's just that limit may sometimes be stated in difference terms from the primary specification.
  
matt lorono
cad engineer/ecn analyst
silicon valley, ca
remind me of....
agent 99:fff"> max, that knife missed you by inches.
maxwell smart:fff"> you think it's some kind of warning?

chris
solidworks/pdmworks 08 3.1
autocad 06/08
no limit at all on how long it can be?
six inches is ok?
three feet is ok?
fifty feet is ok?
at some point the must be a length where you say "that's not going to work."
what is the feature to which the 3 in. min is applied. not totally clear from the orig post.  
while the argument that an 18 foot long piece of material could be the outcome of this callout, i don't think it's realistic nor should it be cause for concern. if you put a tolerance of +/- 1" on the  print and someone cuts it 1.050" over do they really need to cut it again just to knock that last .050 off? the idea is to tell the shop that you want a piece of material no shorter than 3". i don't think any shop is going to ship you a 12' long piece of material just so they don't have to cut 3" off of it but if they do, you'll have extra... if they have a 6" piece laying around, you'll probably get that.
that being said, i am not saying that what i just said can be applied in blanket form across the board. the statement i make is in general, i'm sure there are situations where using min or max is not appropriate but in this case where me2qe gives me the impression that this part is something simple like a rod of piece of tubing i think it suffices. in my specific field, material is bought and sold by the kilo. using min and max works because you're not going to get any more than you ask for.
to answer your question, min/max is addressed in the fundamental rules as a way to avoid tolerancing a part. i don't know if it is addressed anywhere else. i think it has it's place at times but you just need to fully understand the repercussions of using it. the others here gave you the big reasons.
  
powerhound, gdtp t-0419
production supervisor
inventor 2008
mastercam x2
smartcam 11.1
ssg, u.s. army
taji, iraq oif ii
"...do they really need to cut it again just to knock that last .050 off?"
yes, if it is not per print and bigger than the max tol.
chris
solidworks/pdmworks 08 3.1
autocad 06/08