【转帖】do i double the resul

yang686526

do i double the result?
the axis of one hole, which is the datum, to another hole.
the feature control frame says 0.1 to [-a-],[-b-],[-e-]. a 42.5 basic leads from diameter a-e to the perpendicular center axsis of the other hole.
for purposes of capability studies does the 0.1 mean the entire tolerance zone?  and if that is the case should the delta between the true center and the datum be doubled.
joeblock,
   no, delta does not double.  
   the datum hole is located exactly in its correct position, by definition.  the second hole is located with respect to the datum hole.  the 0.1 value is a diameter around the nominal position of the second hole.
   by the way, the hole is the datum, not the axis.  asme y14.5m-1994 does not allow you to apply datums to axes.
   i hope that helps.
                       jhg
drawoh is correct, but in this case the datum axis is established by two datum features.  asme y14.5-1994 states "a datum axis established by coaxial datum features is normally used as a primary datum."  this is the only situation that i am aware of where a datum axis is used as a datum.
joeblock that is the whole point of positional tolerancing, everything comes from the datum, dimensions do not stack up.
one day all parts will be made this way.
sorry i'm late... ditto with the others
chris
sr. mechanical designer, cad
solidworks 05 sp3.1 / pdmworks 05
thank's everyone, but i want to make sure, what i should have said is do i double the result to represent 0.5 to each side of the tolerance zone on a layout report.  just like a diametrical true position.
if you are refering to simply doubling you deviation from nominal to obtain your tp, it works just fine. with a diametrical zone, one doubles the root of (x squared + y squared). so if your y is 0, then you are doubling the root of x squared. the root of x squared = x, so in essence, you are doubling x.
you're doing a capability on a position? seems a little odd as that won't show if the position is deviated to the plus or minus of the basic dim.
in the study i would use +/- .05 not .1.  i'm looking at it like a profile tolerence, the .1 describes the zone of .05 eather side of perfect to the datum.