huangyhg

help determining proper symbol
we are having a bit of trouble with a valve housing coming in from an outsourse machine shop. as you can see, i have the 9.000 diameter circled. this is our trouble area. what is happening is that the valve is measuring 9.002 in the "north/south" direction. however, in the east/west direction we get a measurment of 8.998. we would like to add a control frame to this dimension to help hold it's circularity. what would be the most appropriate symbol?
thanks,
pal
circularity?
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do you mean what control or what symbol?
as ewh says the control you want is probably circularity. the symbol for this in a feature control frame is a circle.
what standard are your drawings to? looks like an older version of ansi/asme y14.5 but i didn't see it stated. i don't think this makes a difference but can't be sure as i've only worked the 94 version. section 6.4.3 in the 94 standard explains its use.
kenat,
just looked again the circled dimension is 9.000 +.000/-.002.
so your measured value of 9.002 is outside the existing tolerance anyway, isn't it?
just adding a control wont necessarily fix things if the manufacturing process fundamentally can't meet the tolerance regardless of how it's specified.
kenat,
i agree with kenat that it's a problem with manufacturing of the part.
but if do wish to control it more, yes circularity should do it. phrased from the book - "a form tolerance is considered when the size tolerance (only) of the concerned feature does not adequately provide the needed control"
are you sending this peace back to be rebuilt or fixed? i know i would.
solid edge v20
heypal,
circularity is the appropriate geometric characteristic to refine the circularity (sometimes described as roundness) of a hole. the elliptical hole that was described would have a circularity value of 0.002.
however, there might be other options. one of them would be to enforce the size tolerance that was specified! if the diameter is measuring 9.002 in one direction, it's out of tolerance. am i missing something here?
the dimensioning and tolerancing on the drawing looks like it was generally done to the ansi y14.5-1982 standard, although no standard is referenced in the title block. there are certain rules in that standard that apply to size tolerances. an important one is rule #1, in which a size tolerance indirectly controls the form of the feature. your may want to consider referencing a specific standard.
evan janeshewski
axymetrix quality engineering inc.
i'm on board with the rest here. you have the hole controlled within .002 by just the size tolerance alone. you should be addressing the issue of the hole being out of tolerance. as you now have it, the hole diameter can range from 8.998 to 9.000 and that's it. the 9.002 is out of tolerance and the parts should be shipped back to the supplier as discrepant.
on a side note, you should remove the rfs modifier from your parallelism callout. it does not apply. you should also remove it from the positional fcf's on both places where they reference datums a and c. datum shift modifiers are only valid on datum features of size.
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thanks for the tips guys. as stated, the part is out of spec to begin with and should have been sent back. however, i regret to info you all of where these parts were machined. let me just say they can not be delivered via a ups truck. not my call, it is just my job to get the drawings correct.
if your requirement is that the diameter is 9.000 +.000/-.002 than the drawing is more or less correct on that issue. a reference to the relevant drawing standard would be good and there's probably some other tidying up to do. however, fundamentally the diameter you're concerned about seems properly defined. you already have effective circularity of .002 unless i'm missing something.
kenat,
we get your inference of where your outsource vendor is. management took their chances and got bit.
as powerhound says, your gd&t feature control frames show that no real standard is being followed, and your datum b, if it had a circularity, callout, might still be wrong, since the part would most likely violate perfect form at mmc, as it now violates rule 1.
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