【转帖】bi-directional top

yang686526

bi-directional top
normally, bi-directional top allow a hole to have more location tolerance in one direction than in another direction, if both direction has same tolerance, can we add the diameter symbol ? before the tolerance as shown on the attached print.
i know the difference between them is tolerance zone, but i am wondering is it the right way to call out the top for this case.
thanks for your inputs
seasonlee

diametrical tolerance zone should be placed on features of size that are round and since your hole is not round, do not place a diametrical tolerance zone in this feature control frame. with dtz, the tolerance is applied in both axis.
i would further suggest that you place the term boundary below the feature control frame. this boundary is the virtual condition boundary which will control not only the location or position of the hole but its orientation. this information is shown in the asme y14.5m-94 standard on page 143 fig. 5-47   
dave d.
agree with dingy, drop the dia symbol.
kenat,
seasonlee,
i agree that the diameter symbol should not be used here.  i don't agree with dave's reason why though.  the diameter symbol should not be used because the tolerance zone isn't cylindrical (because a bidirectional position tolerance was specified) - not because the hole isn't round.  a bidirectional tolerance (with a square or rectangular tolerance zone) can be used with round holes - the shape of the tolerance zone isn't necessarily tied to the shape of the feature.
i think you're right to wonder if this is the right way to call out the top in this case.  an equal bidirectional position tolerance at mmc on an elongated hole is a bit of a mess, and i'm wondering what the function of the elongated hole (it's really a round-end slot) actually is.  the fact that mmc modifiers were used implies that a mating feature (elongated pin or round-end block) will be inserted with clearance on the sides and clearance on the ends. the mating feature will be oriented and located to features that mate with datum features a, b, and c.  is this correct?  if not, then we'll need to encode the position tolerance differently.
evan janeshewski
axymetrix quality engineering inc.
evan:
using your concept, could you please let us know when one might use a diametrical tolerance zone on a feature of size that is not round?
  
dave d.
evan
thanks for your input, the mating part should be a round block in the elongated hole and i guess the elongated hole caused by the 8° slant, for a casting part supplier we are not quite sure its application.
as i know something wrong on the callout, so we measure it with a rectangle tolerance zone even there is a diameter symbol.
thanks for all inputs again
seasonlee

looking at sect d-d, is the hole a counter-bore? if so, you may need another tol for the bottom. the section view looks like it may have a thread also (not clear).
personally, i would remove the two dims and call out a positional tol. otherwise i agree with the others.
chris
solidworks/pdmworks 08 3.1
autocad 08
chris
you are right, its a counterbore hole with .040 depth on a slant.
seasonlee
counterbore on a slant? that would mean the hole is no longer circular but elongated, possibly changing how your dim/tol callouts are used?
chris
solidworks/pdmworks 08 3.1
autocad 08
dave,
here's one instance where i've seen a cylindrical zone used on a non-round feature.  the feature in question was a square hole, and the mating part was the square shank of a carriage bolt.  the client wanted location control that was equal in all directions, and was willing to live with the uncertainty involved in finding the "axis" of a square hole.  the form of the square was close enough to perfect to make the axis quite reproducible.  so we used a position tolerance with the diameter symbol on a square hole.  possibly not quite y14.5 compliant, i'll admit.
  
evan janeshewski
axymetrix quality engineering inc.
evan:
would be most interesting if the positional tolerance was at mmc. wonder what the shape of the virtual condition boundary??? round? square? i do agree that it is "possibly not quite y14.5 compliant".
dave d.