I would use it (I haven't needed to yet... knock on wood) whenever I am concerned that the angle of a hole relative to a mating surface might cause the hole to be out of tolerance.
The example that is comming to mind is a hole into which a long rod or bolt will be inserted and needs to intersect with a feature on another part.
As far as a certain height requirement, no. Height has nothing to do with it. It has everything to do with whether the angle of the hole is critical.
I have only used it in holes. If the customer's product is for example 6" away from my part and they allow a certain tolerance for the holes to line up. If the customer supplies the bolt/screw, I will use PT based on the length of the bolt/screw.
Chris
SolidWorks 06 5.1/PDMWorks 06
AutoCAD 06 ctopher's home (updated 01-18-07)
The application of a projected tolerance zone depend on the features that are required to be inspected. how are you triyng/thinking of applying the tolernace.
It should not be globally applied to all tolerances as this can cause tolerances to fail that in reality will pass and assemble correctly.
The best example of the use of projected tolerance zone would be a pattern of BLIND threaded holes where threaded studs would be assembled. The threaded studs assemble through a pattern of holes of a mating part that, let's say, on .75 inches thick material.
The positional tolerance on the threaded holes could only be confirmed as far as location but perpendicularity could not be confirmed.
Now, if we use a projected tolerance zone on the threaded holes at just a bit over .75 inch thickness, we now can check the perpendicularity of the holes.
The CMM Operator would have to assemble threaded studs into the threaded holes so that the top of the studs would be a bit over the .75 inches.
One would check the positional tolerances on the surface and then again at the top of the studs. In both cases, the positional tolerances must meet the requirement.
A checking fixture could also be developed if the positional tolerances were in a MMC mode.
I believe the answer to your question is that you would use a PLTZ when the relationship to the datum frame is not as critical as the relationship of the hole to hole relationship within that pattern.
