Projected tolerance zone to allow for more orientation error. Help me understand why I may be wrong.

[Nessie_Scot]

I'm working with a fixed fastener design, where the thread engagement of the screw, is about 6x the thickness of the mating part w/ clearance holes (.06" thk PCB sitting on top of screws bosses). Is it possible to absorb addition orientation error using a projected tolerance zone. My thought is that the shorter projected Tol zone, that has the same diametric zone size, would allow for 6x the amount of orientation error. Pic describe it.

 

[3DDave]

It's non-standard to apply feature controls to center lines or axes and the projection is of the indicated surface. Typically there is only one FCF per surface/per geometric characteristic. If the projection is used to go a very short distance relative to the depth of the feature it is likely to accept undesired orientations - calculate the atan(0.008/0/.070) for example.

 

[Nessie_Scot]

3DDave thank you. Eventually the drawing will show just one of these FCFs, and it will be attached to the holes size dimension. I'm trying to illustrate what each of the FCFs would do if the screw hole is off by 1°. The projected FCF would only eat up .0012 of the positional tol, while the regular pos FCF would eat up .0085 at the same 1°. There for, if we don't use a projected tol zone, we might reject good parts.

 

[SnTMan]

Nessie_Scot, that was fast work. Thx

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[3DDave]

However, using dia 0.008 and 0.070 projection allows the hole to reach 6.5 degrees and still meet that requirement. Perhaps you have some other tolerance on the drawing to limit it to 1 degree?

 

[Nessie_Scot]

3DDave, So the projected tol would allow for 6.5° of orientation error. That is kind of what I'm looking for. With out the projected tolerance zone, even a 1° of error would fail the inspection.