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minus-minus tolerance call out
- Thread starter QA4
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powerhound
Mechanical
I just had a discussion about this kind of callout not too long ago. 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. When one of the vslues is zero, always make it the opposite sign of the value with a non-zero value. This way you don't violate one of them. I know one can argue "you know what I meant" or "what else could it mean." all day long, and one would probably be right but this is why we do the things we do...right?
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
@powerhound
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
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
powerhound
Mechanical
So if the dimension and tolerance is .500 -.000/-.005 and you produce it at .498 you have violated the -.000 tolerance because you are at -.002. If you just make it +.000/-.005--which is how it should be done anyway--you can produce the part at .498 and meet both tolerances.
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
powerhound
Mechanical
I guess I didn't explain it well enough. As I see it, the first part of the tolerance is -.000". That means that the deviation cannot be less than .000" from nominal. If you are at -.002" then that's less than .000" from nomimal and thus violates that part of the tolerance. I'm not trying to make a crusade out of this. It's just an observation. The standard is clear on how to represent a nil value and matching signs are not supported. I like the metric system of a zero with no sign.
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
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
CheckerHater
Mechanical
@powerhound:
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
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
powerhound
Mechanical
To your first question: yes, I think that's what I'm saying. I hadn't thought of it that way though.
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
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
I agree that when expressing a tolerance boundary of 0 deviation in a direction, no pos/neg should be applied. It does seem pretty silly. The fact that we're even discussing the impacts of a +0 vs -0 is enough to indicate the silliness of it. In retrospect, I think I've always used zero with the opposite +/- as the other value, so I guess subconsciously I was thinking similar to powerhound, but I think the smarter notation would be to abstain from a +/- on a zero at all.
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5
- Thread starter
- #13
powerhound
Mechanical
No. 1.250 -.001/-.002 is fine because you can be in between the two tolerance values and meet both of them.
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
powerhound
Mechanical
Oh, I see I misunderstood your question QA4. The answer is YES. I thought you were asking if 1.250 -.001/-.002 was an unacceptable way to express the requirement and if it was better to express it as 1.248-1.249.
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II
PH - I see - you are thinking the tolerance is a vector quantity where the sign sets a direction for the boundary.
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.
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.
I don't understand all the talk going on here. Like Cory said: His range is 9.995 to 10.000.
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.
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.
powerhound
Mechanical
Dave, I don't know what scalar math is or how it's different from regular math. Maybe is it regular math and I've just never heard it called that. I don't think the sign sets the direction of a boundary. This is just a simple observation. All I'm pointing out is that if one of the values is -.000 and your actual dimension is -.001 from nominal then you've technically violated that tolerance. How is that not how addition works? I see +/+ and -/- tolerances all the time but they are always non-zero values. This is also nothing like extra trailing or leading zeros. This isn't a stylistic matter since the standard is clear on how to express a zero value tolerance. This isn't it.
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
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
It's really not that hard: if X is any real number, and that real number can have a sign, and zero is a real number, then zero can be a signed real number. If that number is zero and that sign is negative, then that is a valid real, signed number.
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/METROLOGY/Dimensioning 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
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/METROLOGY/Dimensioning 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
powerhound
Mechanical
Dave, I get it. I really do but I don't think we're arguing the same thing. What you seem to be saying is that 0 can be signed either positive or negative and be valid either way. I agree with you. My observation is not about mathematics on the level that you're making it, it's only about what you see on paper. You're saying that +.000 and -.000 are equivalent values, are you not? I'm totally on board. I've also stated that the intent is probably pretty clear and I haven't even argued about the intent. I wouldn't even reject this part if the dimension fell within the intended tolerance band. All I'm saying--and this will probably be the 4th time--is if one of the tolerance values is -.000 and the actual dimension is -.001 from nominal, that violates what is written on the paper.
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
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
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