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.
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.
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)
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.
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?
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.
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.
If you're using a CMM with a decent software/analysis package, it will do the analysis for you. If you're not, then a check gage per Dave will work nicely, depending on the orientation of the datums. Depending on the orientation of the datums wrt the feature you're inspecting, you may find paper gages useful. Is it possible to poste a graphic for reference?
Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development
Joe,
The best way to measure Composite tolerance is of course CMM.
I’ll encourage engineers to use wherever is applicable Composite Tolerance for location and MMC. The intent is to provide a large tolerance for locating feature patterns from a datum reference, such as a part edge (datum –B- & –C-), while providing a closer tolerance of the feature with-in the pattern (in your example 0.005 to –A-). Composite tolerance is used where the location of holes with respect to each other is more important than they location with respect to edge. This method including MMC is providing cost savings during manufacturing process, minimizing scrap rate.
Zarko L.
We currently use a CMM for inspection of finished parts relative to a single datum structure A|B|C without a problem. I thought that with the composite tolerance you have to measure not only each hole relative to datum structure, but each hole relative to each other. In other words, I would have to set my origin at each hole location and then measure the pattern against that. The problem is that my workpiece has up to 150 holes! That's why I originally asked what is the most standard or practical method of measurement for something like this?
Joejack, check your CMM software. A few years ago most packages (Zeiss, Mitutoyo and some after-market) finally provided the ability to process the data for composite positional tolerances. I had almost 150 sub-groups with up to 12 holes at each sub-group on the plate...Mitutoyo's latest software was able to handle it for me as I recall.
Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development
CMM can be used for the PLTZF (pattern relative to A, B & C) but when you get into the FRTZF (inside the pattern) it becomes more difficult.
You would have to pick one of the holes as an origin (datum), rotate the part using another hole and then one can confirm the features inside the pattern. This really isn't correct since you would be confirming the holes relative to 1 hole inside the pattern but it is the only way that CMM Operators do it today in industry.
Of course the best way would have 4 pins of virtual condition size and located on true position (theoretical) and perpendicular to the surface. If they pins fit in the holes and butt up against the datum, the features are conforming.
