【转帖】dimensioning

yang686526

dimensioning
what is the correct method for calling out features (holes)located on a bolt circle on a drawing?
i believe it should be, example;
4x (qty) diameter (symbol)hole size
eq sp bc diameter (symbol) size of bolt circle.
checker says;
4x (qty) diameter (symbol) hole size
eq sp diameter (symbol) size of bolt circle followed with bc.
i would use:
4x dia (symbol) .xxx
eq sp dia (symbol) .xxx bcd.
some checkers like having callouts too wordy.
chris
solidworks 07 3.0/pdmworks 07
autocad 06
i have seen chris's method used, and while it isn't wrong, i prefer "bc" - mainly because it could also stand for "between centers" as well as "bolt circle diameter".  i feel that the extra "diameter" is redundant when using the diameter symbol.
i use bc's so infrequently, that the last time i dim'd one, i spelled it out even more than what your checker asked for.     
matt
cad engineer/ecn analyst
silicon valley, ca
there have been many issues with "eq sp".  we have had many items sent that used this callout and not functioned in the assembly.  nearly any qa department will ask how do you measure "eq sp"?  i would question why your checker allows this.  there is usually just a visual check that it looks ok.  when your parts are much more precise (or even if they are not), then you will need to separate the hole callout, the bc callout, and the degree (spacing)callout.  use the quantity(9) times(x) degrees(40°).  all three dimension items have a tolerance also. the three parts would look something like this, but in the proper locations on your print with tolerances, if there is not a sheet tolerance:
9x ø.125 thru
9x 40°
ø6.250 bc
also, if it is clear that the bc is a bc, then you do not need to have bc on it.  it is not in the standard, but that does not mean that you cannot use it.  the previous information is if you are stating that you follow the asme y14.5m-1994 standard.
marcelino vigil
gdtp t-0377
i'm used to seeing and using (and prefer) the more generic pcdfff"> (pitch circle diameter) ... the holes may not be for bolts.
vigildesign's point is well taken.  i admit that i seldom use it without an angle reference dimension between two adjacent holes, and usually with a true position requirement on the holes.
what is the dimensioning standard that is applied?  how equal are the equal spacings?
these need to be considered in the final solution.
i agree about the use of eq sp.
but, there has been a lot of times i have not used it and the holes were not eq sp because machinist's didn't understand.
chris
solidworks 07 3.0/pdmworks 07
autocad 06
i thought i’d replied to this question in another forum but can’t find it now.
at the risk of being accused of pedantry and assuming you’re working to asme standards:
equally spaced should be eqlsp per asme y14.38-1999 abbreviations & acronyms.
eq is actually equation per same spec and sp is space (amongst others).
bc is in the standard as bolt circle but not bcd (and no d isn’t the standard combination form for diameter).
you can also have a pitch circle, pc or a pitch diameter, pd but pcd isn’t listed.
that said i’d be tempted not to bother with bolt circle or equally spaced and to use positional tol instead with the angle given, something like figure 5-8 in asme y14.5m - 1994
4x dia (hole diameter)
(basic) 4x 90°
(basic) dia (bolt circle diameter)
kenat,
thanks for the reminder. you're correct.
using 'basic', you do not need to call out bolt circle.
it's been a while for me.
chris
solidworks 07 3.0/pdmworks 07
autocad 06