huangyhg

datum pattern callouts
i have a part drawing that contains 6 sheets.
a pattern of 2 holes is called out as datum b on sheet 1.
i need to identify datum b on the other sheets, but it's not necessary to callout the size of the holes. what is the proper way to do this (if there is a proper way)?
do i need to callout the hole sizes every time?
would it be ok to have a leader with "2x" and datum b identifier attached to the leader?
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do you really need to identify the datum on other sheets? that being said, as i do not think this is covered by the standard, i would just create a note pointing to one of the holes stating "hole pattern" and put the datum symbol on the leader.
peter stockhausen
senior design analyst (checker)
infotech aerospace services
jlang, your suggestion is probably technically correct, adding "hole pattern" per peter might clarify it.
do you really have to repeat the datum id? i know we often do it for clarity and it's ok to do it, but in your case it seems it might make it more confusing.
kenat,
if a datum is referenced, should that datum be fully defined (in this case hole size, size tol, gd&t) on the same sheet? or is it ok to have to look back at an earlier sheet?
in my case i have datum b fully defined on sheet 1, but the other sheets have features that reference datum b. so my plan was to identify datum b on every sheet, but only have it fully defined on sheet 1. i figured this would keep things clear without redundantly defining the datum.
jlang, i dont' have the standard to hand but i don't believe there's an explicit requirement to repeat the datum on each sheet.
normally we probably would repeat it on a second sheet to make it easier to read, but as i say, in your case it might add to confusion.
i certainly wouldn't expect it should be redefined as this requires double dimensioning.
kenat,
no, you do not have to redefine the datum to use it again. that would be double dimensioning, unless reference dimensions were used, and that would only serve to clutter the drawing and would not make the drawing any easier to read. to prevent confusion, you can add reference information about the datum feature (such as diameter), but it is not required.
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