Closed Extrusion displays as two open surface walls (no top or bottom)

I’ve attached a file with the problem. (I made a copy and deleted everything else in it.)

I have a curve layer and an extrusion layer. I select the curve layer objects and do a simple extrusion.

It’s pretty obvious which object has the visual problem. If you select the problem extrusion you can see it’s a closed extrusion as it should be. It just doesn’t display as one.

I’m printing the top image in black and white and using that to transfer the image to another substance for an art object I’m making. If there’s no color where there should be, the image doesn’t transfer!

Maiden in the Forest Key Block Extrusion display issue sample.3dm (3.9 MB)

Hi David -
You have 2 very short curves (one of which is self-intersecting).
If you extract the vertical surfaces that are created by extruding those, your object will shade with a top and bottom surface.


I’m really confused!

The Select Self Intersecting Curves command didn’t find them.
Select Open Curve didn’t find them.

The only way I could find them was to draw a selection box around the area you told me they were in.
Even then, I didn’t see them in any view, even if I did the ZS command on them from multiple angles.

How do I find them on my own?

Well, unfortunately, you will probably only find out about this stuff when you have a display error as you did. In these cases, mostly I just isolate the curves that seem to have a problem, then Explode. I then run SelShortCrv and use the file tolerance as the upper length limit. In this case you have 4 curves that are less than file tolerance that will select. Then hit Delete, select all the rest and Join. Afterwards the extrusion displays correctly.

Hi David -

Apart from what Mitch wrote, I used the Rhino 8 WIP and one of those curves was selected there when I used that command…

Thanks! Didn’t know about SelShortCrv!