【转帖】how to measure composite positional tolerance

yang686526

how to measure composite positional tolerance?
what is the best way to measure/inspect a stacked or composite positional tolerance block?  for instance... .016 tp |a|b|c| and then .005 tp |a|
find a job or post a job opening
joe:
i have to ask this question
do you have the modifier "mmc" or a "m" in in circle in the feature control frame. also, do datums b & c have this modifier?
once you answer this question, i can tell you exactly how it is measured.
dave d.
joejack7,
   the composite tolerance block shows the location of the hole pattern wrt the part with all the datums, and a more accurate location of the holes within the pattern.  this is described explicitly in asme y14.5m-1994.  presumably, someone wants to attach a part and locate it to around .016".  they want the holes to line up so that the fasteners pass through.
   an easy solution would be to make a hole template with pins to measure the .005tp.  you would then inspect the position of your template to verify the .016tp.
                  jhg
jhg - no template unless the featuree control frame is shown at mmc otherwise it is in rfs.
dave d.
joejack,
i thought i had made a post before, but do not see here now.
my opinion is that the method can vary depending on the date of the standard that it was based on.  1988 vs 1994.
ringman:
the only change using mmc or rfs with positional tolerances from 88 to 94 is the fact that the 88 standard one must place an "s" in a circle reflecting rfs while the 94 standard assumes rfs unless mmc is placed in the fcf.
dave d.
dingy2,
there is a lot more than the mmc and rfs modifiers that set the 1988 and 1994 standards apart with regards to the composite positional tolerancing.
fwiw the committee spent about 2 1/2 days disecting the fig. 5-26 in the 1994 standard.
the original question on this post did not indicate the standard that was applicable for that matter.  one would need to know,before a conclusion could be made. hopefully the drawing was proper for its date of preparation. if not, problems on interpretation are difficult to resolve.
adding to the situation, is the fact that the interface component is an essential item to determine the proper tolerancing.  (there was no interface component for the fig. 5-26)
ringman:
figure 5-26 on page 125 is not a composite feature control frame but 2 single segment feature control frames.
again, one cannot suggest how to measure a composite feature control frame unless we know the modifier (s) or (m) from the 88 standard or (m) from the 94 standard.
dave d.
thanks all,
sorry for the delay, but here is more info...
the standard is the 94 - the callout does have the mmc at the positional tolerances but not onthe datum callouts.
standard "hole" pattern callout, but my issue is that the material is composite sandwich with honeycomb.  the true feature will be difficult to measure so therefore we considered cutting a different material and proving our process capabilities.  the issue is again...  what is the current standard for measuring this type of feature?
thanks.
since the composite feature control frame does have a mmc application on the position and not the holes means that you would have a checking fixture.
the top section (pattern) (pltzf)would have locating pins on the checking fixture of virtual condition size. one would locate in the datum holes using tapered v cones.
the bottom section would again be a checking fixture. yes, you need 2 fixtures. the locating pins would again be at the virtual condition size (much tighter tolerance) and located on the surface. this is within a pattern (frtzf) and oriented to datum a.
both can be done on a cmm but the software much be able to calculate tolerance on each hole depending upon size.
dave d.
joejack,
it appears that you are locating holes in a honeycomb panel. the edges might serve as datum features. are there inserts which will be installed at a later time perhaps?  could you provice more info as to the fasteners used and sizes?  this would enable a better assessment.
it appears that the tolerance you are specifing is overly restrictive, but without additional information that is only a guess.