minus-minus tolerance call out
minus-minus tolerance call out
(OP)
Got a print dimension call out that reads 10 -.000 -.005. Is my range .005 to 10?
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minus-minus tolerance call out
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RE: minus-minus tolerance call out
RE: minus-minus tolerance call out
RE: minus-minus tolerance call out
RE: minus-minus tolerance call out
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
RE: minus-minus tolerance call out
I don't understand your statement that:
"When you put the same sign on both tolerance values--when one value is zero--you have a situation where you are going to violate one of them."
What violation is inevitable? I don't understand what you're seeing as a difference between +0 and -0, I guess.
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: minus-minus tolerance call out
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
RE: minus-minus tolerance call out
RE: minus-minus tolerance call out
I agree that tolerances set boundaries but the boundaries should be stated correctly. This is why we got away from notes like "dimensions to be central within .010."
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
RE: minus-minus tolerance call out
If I understood correctly, .500-.000 means .500 MIN and .500+.000 means .500 MAX, is that right?
Can you provide reference to any source?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: minus-minus tolerance call out
To your second question: I have no reference that says how a tolerance like this SHOULD NOT be expressed, but ASME Y14.5-2009 says how it SHOULD be expressed. Again, this is just an observation. I'm not on a mission to prove anyone wrong or right.
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
RE: minus-minus tolerance call out
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: minus-minus tolerance call out
RE: minus-minus tolerance call out
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
RE: minus-minus tolerance call out
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
RE: minus-minus tolerance call out
Since this is scalar math, that isn't correct. This is obviously the case in that +/+ tolerances and -/- tolerances for any values are acceptable and frequently used. That one of those limits is equal to zero doesn't change how addition works.
The rest is just a stylistic thing. Like useless leading or trailing zeros being included or not as an indicator of whether metric or decimal inch dimensions are being used. The drafter is already is obliged to identify the units involved. The math isn't violated by extra or missing zeros; it's just a thing that checkers can whine about that has no effect on the understanding of the drawing.
RE: minus-minus tolerance call out
If you are .000000001 under 9.995 - your part is undersize. If you are .000000001 over 10.000 than your part is oversize.
What is so difficult here? 10.000 -005 would be good enough. The minus in front (-000) is not needed.
For those working with ISO/DIN 286 look at all you H - h tolerances.
RE: minus-minus tolerance call out
Juergen, I don't disagree that the range is 9.995 - 10.000. What I'm pointing out is that I think the zero value should have the opposite sign of the non-zero value. I've already stated my reason for thinking so, ad nauseam. There's really no other way I can say it.
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
RE: minus-minus tolerance call out
Since an acceptable value is any one between and including a defined pair of real numbers and that range is described by adding a real number representing the nominal to signed real numbers representing the acceptable limits to deviations from than nominal, then there's no reason not to use a valid, real, signed number, which includes '-0,' as one of the acceptable deviations.
I'll just say that it isn't possible to violate a single limit. Every tolerance has two boundaries. Sometimes one of those is implied to be plus or minus infinity; sometimes it is implied to be zero. But if I say the nominal is X and am told only that one tolerance for deviation is Y, then no value can be accepted or rejected. In plain words, saying the value has to lie between X+Y and X+ ... where ... is not defined, does not accept or reject any value.
To better understand D&T and understand scalar and vector notation buy a copy of ASME Y14.5.1 Until then, check ftp://210.212.172.242/Digital_Library/Mechanical/M... and Tolerancing Handbook/81314_07.pdf or Google search for y14.4.1 pdf site:210.212.172.242 for the article/chapter "Mathematical Definition of Dimensioning and Tolerancing Principles" by Mark A. Nasson, Draper Laboratory, Cambridge, Massachusetts
RE: minus-minus tolerance call out
The whole reason I had even had this discussion a few weeks before this thread was because the was a print that came around that had the tolerances like this:
-.003
-.000
The thing that struck me was that since this seems to be a unilateral tolerance in the negative direction then shouldn't the zero be the top value? I've never seen it like that. So then the possibilty of a typo came up. Maybe the values are correct and the signs are wrong. The positive value goes on top so was it actually supposed to be +.003/-.000? The third option was that the intent was +.000/-.003 (or -.000/-.003) and I think that's what they settled on. I don't know the outcome but I think a shop would be remiss not to at least question a dimension and tolerance written like that. I think that how a dimension and tolerance is stated on the drawing, mathematics aside, makes a significant difference in how it is to be interpreted. I'm sorry I ever brought this up. I thought it would make for interesting discussion which--up until you decided to refer me to the book of the month club--it actually was.
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
RE: minus-minus tolerance call out
Would +.010/-.000 be violated by a +.001 deviation?
For certain, by what you have written so far:
+.000/-.010 is not violated by a -.001 deviation, but
-.000/-.010 is violated by a -.001 deviation.
The problem you had should have had speculation stop immediately at a call to the responsible engineer and whoever from manufacturing and QA/QC signed the drawing as ready for production. No need to guess about the signs or anything else.
Of course, this would not detect other interpretation errors, but having engineering review and sign off production and QA/QC plans would close the loop as much as possible and there would be no need for a call for this case at all. I doubt many companies do this, mostly because the cost of defective interpretation is preferably a hidden cost that comes in when schedules are delayed when manufacturing/QA/QC delivers unusable product with an argument about drawing deficiencies.
As a side note, it used to be that manufacturing wanted the first tolerance to be the first limit hit; in boring a hole the -.003 tolerance would be place above the -.000 tolerance. That way missing the tolerance would leave more material and an acceptable part. If they over-bored the -.000 tolerance, they would have a scrap part. The opposite was true on external features.
RE: minus-minus tolerance call out
Thanks!
RE: minus-minus tolerance call out