3D Printing Lines Radiating out for each Circle Segment

I’ve been 3D printing for over a year. Noticed that some models have lines radiating out from a circle. Sometimes many of the lines will join at a location. Some circles don’t have the lines.
I recently encounter a problem printing where there were a was common flaw printing the circle. So, I added the lines (not knowing what I was doing) and it solved the problem, Why?

This is the correct image.

If you are asking about the source of the edges we see on your second posted image we would have to examine the actual .skp file to figure out exactly what’s going on. How are you creating these shapes? There are generally two scenarios that I can think of that create this kind of coplanar or near coplanar radiating edges.

One is that in your modeling process you are scaling or otherwise modifying connected pieces of raw geometry, which drag the surfaces and edges they are connect to into triangles as they move.

The second (my guess) is that you are importing these files from another file type into SketchUp, such as importing a .stl, or .step. STL is a tessellated (triangle based) format and if you import into SketchUp you can often see many surfaces broken into coplanar triangles. If the edges are truly coplanar with adjacent edges then you can erase them and the surface will stay a plane, but if the nodes are even slightly out of plane the edges will have to stay for the shape to remain a solid and be printable. You can hide the extra edges, or soften/smooth the entire unit.

It is an imported STL file . I was enlarging a circle.
I closed the small circle and deleted associated lines. Then created a larger circle and push it through to the other side. Then printed the model. There were physical breaks on the x axis. No visible flaws in the file. Added the lines to the circles and reprinted . Noo physical errors and the model was as expected. Then i asked what did the lines provide?

The lines do not provide anything. They are an artifact of the file type you have imported from (.stl). If you made the shape in SketchUp you would not have them. If adding lines made a file printable it suggest that the surrounding nodes were not coplaner and that adding an edge allowed faces to form.

This is hard to say without seeing the actual model.