[deadlykitten]

derogation

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

[mactec54]

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"

[deadlykitten]

maybe there is a more appropriate english term for it

An exemption from or relaxation of a rule or law

dimension's tolerance is law; derogation is the exception

[deadlykitten]

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

[deadlykitten]

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

[mactec54]

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.

[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

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