Circle problem with .stl (holes "heal" over)....?


i have been using sketchup (and it’s predecessors) for 15 year or so. i am currently using Make 2015 pro on a mac os x system. i am trying to make a cylinder with another cylinder running down the center; when i try to modify the inner wall of the outer cylinder by deleting a segment, the center hole keeps “healing”. what is causing this and how can i keep it from happening…? i have searched and searched for an answer and am getting desperate.

a worse problem is that when i create a model for 3d printing, export it to .stl it will look fine in meshlab and then when i submit it to shapeways the “holes” often heal up. the sketchup model looks fine, the .stl model looks fine in meshlab, but the shapeways rendering is “broken”…?



Could you share an example SKP file that shows this issue?


Are the faces orientated correctly (front outside)?


It may help, but not for this issue…


i have a picture but can’t seem to post it…?


The few seconds I saw your image it looks like all the faces were reversed.



it doesn’t make a difference if the faces are reversed. i has the same problem both ways.


Yes, all the faces are reversed. that’ll be no good for 3D printing.

What are you trying to achieve when you remove that edge?


How does sharing an image of the SKP icon help?


CircleSurfaceProblem question.skp (205.2 KB)

sorry - i normally don’t use this site - an my learning curve is a little steep.


the image on the right is what you get when you delete the top segment of the first inner circle.


OK. So explain what kind of modification you are trying to make to the inner wall. Why are you deleting that edge? It’ll leave a hole in the inside wall of the tube. What is it you want as the end product?

The fact that SketchUp is skinning over the opening when you delete an edge as shown in your second copy is a normal behavior. You can remove it again.


perhaps i am mixing two issues that i think are related… go to the second part of my issue. i export what i believe is a fine model (.stl) from sketchup - it looks fine in meshlab and any other viewer - and shapeways puts a skin over the hole. i think the second circle has some “invisible” skin associated with it that i cannot see in sketchup to remove. this problem occurs when i export with .dae as well. tying to fix the .stp file with netfab doesn’t fix it…?
i am baffled - shapeways says it’s not their issue.


There is no invisible skin over the hole in your model. A skin will be created when you delete an edge on the inner circle as you showed in your model and the image.

Very likely the problem is because you have reversed faces. All faces should be correctly oriented with the only white front faces visible. Try correcting the face orientation and also make sure you wind up with a solid component or group and try uploading that to Shapeways.


Maybe it does?


i think i can work around the issue if i leave a line in the two surfaces…? this picture shows what happens when i delete a segment when the two “anchor” lines are in place? what is going on?


I don’t know what to tell you. You’ve been using SketchUp for 15 years so none of this should be new. You will not be able to 3D print the thing on the right because you are missing a face and an edge. Both of those are required to make it solid for printing.

As I already said, the skinning over is normal behavior when you remove even part of the edge of a hole through a 3D shape.


Here. I drew a clean version of what it looks like you were trying to draw. Upload that to Shapeways and see what you get. Be aware that Shapeways may put in a support mesh to connect the inner and outer tubes. Since they aren’t otherwise connected, it would probably make more sense to run them as separate parts.

CircleSurfaceProblem question.skp (132.0 KB)


this isn’t really part of my model - it’s to show you what the general issue is. why does 3d printing care which way the faces are oriented if they are all the same texture?