Projection Callout Question

[[Ca...]]

Firstly, I'm full aware of how to check a location with a projection symbol. That said, I've never seen a projection callout listed below the FCF. This location is for a threaded through hole. My only guess, beyond it being an accident, is that the intent is to project the location requirement from both sides of the threaded through hole. Thoughts???

See attached.

Capture.PNG

[[Br...]]

That is the old way projected tolerance zones were shown with a feature control frame. The 1994 revision of Y14.5 changed this to place the Projected tolerance zone symbol within the feature control frame.

Regarding your other question, on thru holes, it needs to be indicated to show which direction the tolerance zone applies using a heavy chain line with a dimension on a drawing view. On blind holes this isn't necessary.

If you cannot ask the engineer to make a drawing change or identify for you the direction of the projected tolerance zone, all you can do is make an educated guess as to which way the fastener would probably insert into the hole. Try to identify mating surfaces usually represented as a datum feature. You could do a projected tolerance zone on both sides like you said to be safe, but this could make it tricky to manufacture, especially with tighter tolerances. Really, the engineer needs to clarify this. It shouldn't be on manufacturing and metrology to figure out the design intent.

[[Ca...]]

Thanks Brett!

The print doesn't indicate which surface is the projection origin, and the part is symmetrical, so an educated guess about assembly is sort of out. One of the surfaces the thread intersects is a datum, so I guess I'll program to project from there(?). I'll make a note, and when we start making these things, I'll verify with the production floor that we're both checking it the same way.

Thanks again Brett!

[[Br...]]

Good luck Casey. The datum features are supposed to be selected based on the mating interfaces of the part. (Doesn't mean that this was the case.) So its typically safe to assume if the primary datum feature is one of the surfaces the holes pass through, its probably also the direction of the projection. Of course, nothing is certain if its not specified.