Parts are out of tolerance. We accepted them because they are still usable.
There is a word in Chinese that translates to "accept on deviation". It is used when parts measure outside of tolerance, but they are accepted. What is the word in English for this?
Re: Parts are out of tolerance. We accepted them because they are still usable.
derogation , 2nd/3rd level tolerance :)
Re: Parts are out of tolerance. We accepted them because they are still usable.
Quote:
Originally Posted by
PhilCNC2020
There is a word in Chinese that translates to "accept on deviation". It is used when parts measure outside of tolerance, but they are accepted. What is the word in English for this?
This is an interesting, subject.
If the part had to fit something, and it is out of tolerance, then it is Scrap.
If it was accepted, then the part most likely did not need to meet the drawing tolerance to start with.
Sometimes the parts can be reworked to save the loss of material and time. if it can't be reworked then again it is Scrap.
accept on deviation, can be a number of words. deviation being the best word that would describe an out of spec part
Re: Parts are out of tolerance. We accepted them because they are still usable.
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Originally Posted by
deadlykitten
derogation , 2nd/3rd level tolerance :)
derogation :rolleyes:
Re: Parts are out of tolerance. We accepted them because they are still usable.
Not to design constraints........SCRAP!
Re: Parts are out of tolerance. We accepted them because they are still usable.
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derogation :rolleyes:
hy mactec :) i am not an english native; derogation is the best translation that i could find
technique of derogation is not common, and is specific to certain mass production areas
for example, a technical drawing is paired with a list of specific details for production, in order to eliminate doubts and to reduce decision strain, like helping/encourouging a technical director to take a specific proven aproach, telling what is allowed and to what degree; it realy makes life easier, because it narrows down the number of different approach interpretations of a technical drawing to a few real possible solutions; one of such points can tell that a certain dimension is allowed to be out of main tolerance, as long as it is within a 2nd tolerance, but not above 1.5% of overall quantity; 3rd tolerance may be allowed only for <1% or overall quantity ... depends
such drawings are clear, yet elaborated for immediate production start; even the dimensions are drawned corectly, and not the other way arround; the list of details is about real situations; once done, it gets stamped, registered, and archived; is the oposite of the common nowadays situation when a young employ is droping nonsense dimensions from a cad/cam system / kindly :)
Re: Parts are out of tolerance. We accepted them because they are still usable.
Quote:
Originally Posted by
deadlykitten
hy mactec :) i am not an english native; derogation is the best translation that i could find
technique of derogation is not common, and is specific to certain mass production areas
Not even close to anything to do with being manufactured or of mass production.
An exemption from or relaxation of a rule or law.
"The massive derogation of human rights"
The perception or treatment of someone or something as being of little worth.
"The derogation of women"
Re: Parts are out of tolerance. We accepted them because they are still usable.
maybe there is a more appropriate english term for it :)
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An exemption from or relaxation of a rule or law
dimension's tolerance is law; derogation is the exception
Re: Parts are out of tolerance. We accepted them because they are still usable.
hello :) here are a few examples of custom details that may accompany a technical drawing :
... dimensions of group A are corelated : during setup and inspection, is enough to measure only one of them ( so to make life easier when inspecting )
... dimension X can be derogated to "?" among a certain region of the part, or under "condition" ( so to by pass original tolerances, without losing functionality )
... dimension T,U,V are for the tools ( thus they won't be inspected on part )
... dimensions marked with * will be inspected/machined in assamble, "as fallows" ( for example, is used when the assamble tolerance must be < tolerance sum of some of its components )
... table showing inspection method for some dimensions ( eliminates subjectiveness mostly for critical aspects, thus using a single method, even if there are more theoretical solutions; may be an instrument, a device, a paired piece, etc, with serial number and it's own quality control )
... inspection frequency class : critical, major, minor, etc ( each class has it's own % of allowance )
... type : prototype, 0 serie, mass production ( so to be handled only by personal with apropiate skill level / clearance )
... tool or fixture marks are allowed on surface "?", as long as "condition" ( no need for the part to be silky smooth all the way arround )
... profile W is allowed to be manufactured accordingly to variant "?"; in this case, also "something else to be done"
... material "?" is allowed temporarely, until "condition"
... edge C will not be chamfered ( thus in case you thought about it, just leave it )
... occasional, if "inspection method 1" is not good, then part can be accepted if it passes "inspection method 2"
there are specific details for each phase, from material quality, transport, heat treat, preparation, machining, deburing, asembling, painting/surface treatment, inspection zone, to boxing, labeling&warnings ( don't drop / haha ), stack height maybe if it can't move, capability, etc; heavy industry / kindly :)
Re: Parts are out of tolerance. We accepted them because they are still usable.
hello again, there is something more : under a certain line, discusions are about dimensions and tolerances, but over that line, what matters is functionalty / purpose of final product, to be delivered to the client
with that in mind, reversengineering becomes easier, some noncritical tolerances are droped only to be droped, like we need a tolerance here, or something; mostly, for a given part/assamble, only a few dimensions really matters, others are less important, and some exist because they must exist; is that simple :)
for any dimension, base value means resistance, and tolerance means functionality; a technical drawing is just a method of comuncation
explain how a part works to a group, then ask each one to create the drawing for it : only a few will make it simpler, and those simple ones can actually be understood by everybody, while complex ones are messy and take more time to digest
there is a trick to transmit derogation inside a drawing, in a simple manner : enlarge tolerance towards the non-critical limit, with a range that is way larger then process precision; for example :
... for roughing instead of 270+0.5 i may use 270.5-5
... for grinding instead of 100+0.02+0.035 i may use 100.02+0.03
normally, this is not allowed to do without an explanation; i like to avoid explaining, by simply knowing that the drawing will be handled by persons that know the workflow, so they don't need futher explanations
i don't like using dimensions like A+t1+t2, but like A+t, thus less text ( more white space on paper helps ); also, if i enlarge the tolerance, the "trade" is for the final dimension to be kept towards the base value; let's take again the previous example :
... 270.5-5 to be machined towards 270.5, and not towards 265.5
... 100.02+0.03 to be machined towards 100.02, and not towards 100.05
thus is possible to use the base value of a dimension to transmit where to position machining accuracy inside the tolerance field; kind of unwritten law, that makes life easier in many situations, unwritten, because there is no technical drawing rule to tell if a tolerance should be kept towards a limit or other, as a basic tolerance is considered with same importance among it's entire range
with such tricks, is possible to force the limit of real part dimensions accuracy in a derogated manner; this is rarely discused, and common method is machine to the middle of the tolerance, while in some cases is not ok to go for middle, and also is hard to narrow down the tolerance, as it gets close to a real limit of measurement acuracy / kindly :)
Re: Parts are out of tolerance. We accepted them because they are still usable.
Quote:
Originally Posted by
deadlykitten
with such tricks, is possible to force the limit of real part dimensions accuracy in a derogated manner; this is rarely discused, and common method is machine to the middle of the tolerance, while in some cases is not ok to go for middle, and also is hard to narrow down the tolerance, as it gets close to a real limit of measurement acuracy / kindly :)
A Tolerance on a part Drawing is what the part is allowed to be within stop the Bs.(wedge)
You should not copy from web pages, unless you know the subject matter, you are posting about, try using an automated spell / grammar checker as well. :)
Re: Parts are out of tolerance. We accepted them because they are still usable.
mactec, have you seen factory documentation that alows multiple sets of tolerances ?
have you negotiate technical drawing conditions, so to ease up production ?
what is a revision before being written on the technical drawing ? is a situation for some parts that perform better at some criteria, even if they don't meet the initial conditions ( thus initial conditions don't cover such a change ); to allow this officialy, for the future, then a revision is done; this revision may allow :
... only the new variant to exist
... both variants to exist, maybe with a time limit for the 1st one, after which only the 2nd one will be used
a revision is kind of a derogation, but more limited; main difference between them is that:
... a revision targets final product variants
... a derogation targets also intermediate productions phases, aocrdingly with process accuracy
Quote:
You should not copy from web pages, unless you know the subject matter, you are posting about, try using an automated spell / grammar checker as well
with all respect, i am just saying, i am not here to convince you :) come on, please, don't make such supositions
Re: Parts are out of tolerance. We accepted them because they are still usable.
Derogation is fine.I live in a country that spent many years functioning with derogations from restrictions that applied in bordering countries.When it is usually applied to for parts it can be an indication that the guy in the drawing department has taken the default CAD tolerance in the template and applied it to a place where that level of precision wasn't actually necessary.The derogation comes from seeking clearance to use the part because it will actually function satisfactorily if a couple of dimensions are a little outside an arbitrary tolerance.It can also be referred to as a concession from the designer that such a deviation will be accepted because of the need to get an item into use in less time than it would take to make a replacement.Some jobs require the item to be in use in a hurry and utter adherence has to be set aside temporarily.
Just for clarity I have an amount of experience with parts that absolutely have to be within stated tolerance to function properly and those not conformant get scrapped.Applying extremely tight limits to simple brackets and the like is an all too common neophyte error.I have to congratulate deadlykitten on such accurate usage of a second language,few of us could communicate so effectively in a language other than out own.
Re: Parts are out of tolerance. We accepted them because they are still usable.
Quote:
Originally Posted by
deadlykitten
mactec, have you seen factory documentation that alows multiple sets of tolerances ?
have you negotiate technical drawing conditions, so to ease up production ?
what is a revision before being written on the technical drawing ? is a situation for some parts that perform better at some criteria, even if they don't meet the initial conditions ( thus initial conditions don't cover such a change ); to allow this officialy, for the future, then a revision is done; this revision may allow :
... only the new variant to exist
... both variants to exist, maybe with a time limit for the 1st one, after which only the 2nd one will be used
a revision is kind of a derogation, but more limited; main difference between them is that:
... a revision targets final product variants
... a derogation targets also intermediate productions phases, aocrdingly with process accuracy
with all respect, i am just saying, i am not here to convince you :) come on, please, don't make such supositions
Yes, but these posts, don't address what was being asked
Re: Parts are out of tolerance. We accepted them because they are still usable.
Quote:
Originally Posted by
routalot
Just for clarity I have an amount of experience with parts that absolutely have to be within stated tolerance to function properly and those not conformant get scrapped.Applying extremely tight limits to simple brackets and the like is an all too common neophyte error.I have to congratulate deadlykitten on such accurate usage of a second language,few of us could communicate so effectively in a language other than out own.
Derogation does not mean " restrictions " as you have posted, just the opposite. :)
In its widest sense, the word ‘derogation’ refers to an exemption from, or relaxation of, a rule or law. so could be used but not practical, for it to be used with drawings, no matter where you are from.
In the real world this would not be used in any normal mechanical part drawing :)
No excuse for language, many of us are bilingual. :)
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Re: Parts are out of tolerance. We accepted them because they are still usable.
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guy in the drawing department has taken the default CAD tolerance in the template and applied it to a place where that level of precision wasn't actually necessary
hy routalot :) if i may, that's a mistake, not derogation
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The derogation comes from seeking clearance to use the part because it will actually function satisfactorily if a couple of dimensions are a little outside an arbitrary tolerance.It can also be referred to as a concession from the designer that such a deviation will be accepted because of the need to get an item into use in less time than it would take to make a replacement.Some jobs require the item to be in use in a hurry and utter adherence has to be set aside temporarily
examples are good, but more like particular cases, because derogation is :
... not based on arbitrary tolerance
... not always about time management for a single item
... not a temporar phenomen
what you described, is on the fly adaptation, thus dynamic behaviour, that exists, and is specific to those activities where such freedom is allowed
if i may, derogation starts from a corect drawing, and is never designed to corect human erorrs; it handles only some statistical proces deviations that do not comply with initial tolerance
derogation is not there to fix mistakes, thus is not there to fix something done wrong in a previous phase of the workflow; it is there to assure less interuptions only from the current phase
even if it is expresed as a larger tolerance, it is actually much more related to process stability, and less to the drawing; the drawing is only it's form of expresing the limits; for example, there may be repetitive similar assambles, typeA and typeB, typeB being twice as big as typeA; typeA and B share similar parts/subansamblies, only that those are not proportional; however, during manufacturing, they share very similar phases
as phases become repetitive, in mass production, sudden particular cases appear, and a solution is being proposed, that lately it may become a derogation; that derogation will be printed in each drawing that requires that specific machining phase; as a consequence, only by seing a drawing that is derogated, but without knowing the workflow, is hard to understand what was the purpose of the derogation, so from this reason, derogations have to be acompanied by labels, by explanations, so to make them easy to understand by someone who wasn't there when the derogations was implemented; in time, common derogations became standard across similar industries, but their core meaning rarely reached the common operator, because they are being handled only by specific personal that is responsible with overall production flux; such documents are not for common acces, but only to be handled by advised personel
derogation is based on real process scenarios, is kind of a feedback; it is part of factory documentation; derogation folows a general rule, as shown in attached image, but also there are exception
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I have to congratulate deadlykitten on such accurate usage of a second language,few of us could communicate so effectively in a language other than out own
thank you routalot, kind words; i am considering to go at an english contest next year / haha :)
Re: Parts are out of tolerance. We accepted them because they are still usable.
The derogation comes from the usage of parts that are outside the tolerance and applies to the use of them after seeking assurance that it will be permitted in this particular set of circumstances.It does not remove the need for the parts to conform but it acknowledges that they are not as they should be and may be used with care.Another word that might equally well be applied is a dispensation to allow the use of them.
Re: Parts are out of tolerance. We accepted them because they are still usable.
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after seeking assurance that it will be permitted
hello again :) yes, exactly; depending on organization, one may take such a decision on it's own, or after consulting with the client, or through a comite, etc
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It does not remove the need for the parts to conform but it acknowledges that they are not as they should be and may be used with care
in some cases is imposed a % limit, thus it generates quality clases within a fix ratio, and after that each class is threaten differently
in other cases, there is no % limit, and all products are machined without taking into acount the differencies generated from a custom phase
it depends / kindly :)
Re: Parts are out of tolerance. We accepted them because they are still usable.
work it might, shine it must
