How do I prevent vertical lines when pushing a circle into a cylinder?

I tried to weld the edges of this coffee table before pulling it, but the P command after Welding deselected the edges. Even selecting the whole table had the same effect.

Oh I see! It must be done IN ADVANCE. Well that’s a game changer. Thank you very much!

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Yes, but your English is too good. I still don’t quite get how Sketchup decides, without an animation to help me understand.

@nmason has given me an awesome tip with Weld Edges. It’s a game changer.

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My models will be much cleaner from now on :slight_smile:

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I’m not in a position to make an animation, sorry, but here is a hopefully simple experiment that you can try to experiment with the two different cases (arc/circle/welded perimeter edges vs. plain edges).

  1. Create a circle of any convenient size and modest number of segments (nether property matters significantly) flat on the red-green axis “ground” plane. Say a 4 inch diameter circle with 24 segments.

  2. Activate the Line tool and draw a zig-zag series of edges (4 or 5) across roughly the middle of the circle. The idea is to split the circle by isolating a jagged chord of the original circle. The original circle should now be separated into two arcs (in SketchUp terms) with the jagged line cutting between them.

  3. Select either of the two perimeter arcs and delete it. The result should be a roughly semi-circular face whose perimeter is composed of an arc (which is itself composed of perhaps 10 or 15 edge segments) and 4 or 5 additional individual edges (the zig-zag you drew across the circle).

  4. Activate the Push Pull tool and extrude the jagged semi-circle up or down into a 3D shape.

Now look at the faces that form the vertical sides of the shape. The faces that are bounded on top and bottom by the arc portion of the jagged semi-circular starting face should form a “surface” (in SketchUp terms) that is smooth with no visible vertical edges, and who’s 3D rendered shading is continuously blended around the curve. In contrast, the faces that are bounded on top and bottom by the zig-zag line will be separate faces with visible vertical edges, and whose 3D rendered shading shows flat faces with no fine gradations of shade.

For a further experiment you could Undo the Push Pull operation, select the arc of the starting flat face, and perform the Explode function (which causes SketchUp to forget that the series of adjacent edges are an arc). The entire perimeter of the starting semi-circular face is now composed of individual unrelated (but touching) edges. Activate the Push Pull tool and extrude the face into a 3D object again. The new faces forming the vertical curved side of the shape (above and below what had previously been an arc of the starting 2D face) will have visible edges between them, and the 3D rendering shading will be flat - the same as the new vertical faces formed above and below the zig-zag part of the 2D starting perimeter.

In summary, when a series of connected edges of a starting 2D face are related by virtue of being an arc or circle or welding, then the corresponding curved face generated by Push Pull will be automatically softened and smoothed into a single large “surface”. When the connected edges of a starting 2D face are simple unrelated edges (other than touching each other), the faces generated by Push Pull will not be softened or smoothed. They will be separate faces each with visible edges and flat shading.

You are filling the forum with questions that are learned in the initiation courses, it is what you have been advised in many of the posts you have made.
Filling the forum with basic things does not help anyone, we all try to search first and if it is difficult we resort to the forum because there are many people who generously spend their time to help, but as they do it generously I do not think it is appropriate to abuse their generosity.


Should this forum ban questions whose answers can be found in the courses? When I become an advanced user, should I tell people to go and find the answers themselves? I am grateful for those who don’t tell me to ‘Google it’ or ‘Read the course material.’ I strongly disagree with your sentiment about questions creating pollution on this website, but if you do feel strongly about it, ask the owners of this forum to ban questions, or if that fails, there is no obligation for you to help people - or police them on behalf of this website. Question-blocking and sending people on wild goose chases to find answers is unquestionably bullying. Right now it appears you are siding with the bullies. I don’t know why. Let’s hope this isn’t a widespread part of the culture here.

You must weld the lines before extruding or smooth edges either from the soften smooth edges tray or using the eraser tool taping the Ctrl key before using it.

Been trying for months to find a way to eradicate a seam.

Nothing I do will smooth it out; it always remains as a visible “bump”, complete with shadow.

Alas, if it were only as simple as that.

Unfortunately there is no wall to look inside.

Sorry to @Zxen for hijacking his thread, but at least it’s on-topic.

It’s been softened, it’s been smoothed, it’s been softened and smoothed, it’s been neither a hundred times. It’s been deleted and redrawn a hundred times. I’ve started from scratch a hundred times. I’ve tried scaling, I’ve tried everything I can think of, but pushing those lateral cylinders through the vertical cylinder always results in visible seams, no matter what. I may redraw the entire thing again, but with more segments – 60? – and see if that helps. I’ve been deferring this because of my recent aversion to circles with “too many segments”.

There’s really not much more to it than the images depict. It’s a simple single-walled vertical cylinder with four simple smaller cylinders pushed through horizontally. And yes, I’ve tried pushing them through individually and as two long cylinders passing through both/opposite faces at the same time. Nothing makes any difference.

Maybe it’s just some weird and rare combination of circle diameters, orientations and segment counts? I don’t know.

@anon91144253, have you inspected the wall with the help of a section plane ?

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In that specific case I also suggest that you post a small SKP file that includes the cylinder (and as little else as possible for simplicity). There is a chance that someone will discover some aspect of the geometry that causes the rendering irregularity.

On the other hand, I have seen many cases in my own modeling where the native rendering (in the normal SketchUp workspace window) has discontinuities. I attribute it to quirks in OpenGL or maybe SketchUp in how the SketchUp faces are sometimes divided into small thin triangles for rendering. It is sometimes possible (and kind of entertaining) to see the underlying triangulation of a SketchUp face when Z-fighting occurs. If you orbit around the model the rendering engine will reveal the little triangles.

To be clear: the triangles to which I refer are not bounded by edge entities in the SketchUp model. Consider a single SketchUp rectangle, which has four edge entities and one face entity. Now put a rectangular hole somewhere in the middle of the face. Four new SketchUp edge entities are created, to accompany the four original edge entities and the one face entity (whose shape has changed, but it remains one face entity). To render that one face, I think the underlying engine sub-divides the face into 8 triangles and renders each sub-triangle. These sub-triangles are formed of borders connecting from corner to corner, similar to the following manually-drawn illustration:

When the SketchUp face entities are bordered by SketchUp edge entities that are smoothed (such that the 3D shading blends or has gradations on “curves”), I think there are cases when the rendering engine doesn’t do an optimal visual job of applying proper shading to the implicit sub-triangles. From some angles the rendering can look great, from others not so great.

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cursed_tube.skp (46.7 KB)

You participated in a thread of mine: What is the reason that some actions breaking circles and arcs?
Broken circles and arcs can be the cause of those lines…

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cursed_tube-3.skp (222,2 Ko)

I just had a bash… and predictably if you augment the number of sides to the circle used to create the big cylinder, you get a better result… in my test, here they are 96 then 148 sides… But as SU doesn’t understand the concept of “circle” with infinite “sides” there will always be some lack of smoothness.
Anyway, hope that helps…

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If you orbit around the copies with 96 and 144 sides per circle, does the small visual ridge between the two holes appear from some angles?

Hi. I tried redrawing it with both 60 and 96 segment circles but there are still seam lines due to broken geometry. The only way to avoid the lines is by not intersecting hidden geometry lines, but that means stop sign scale circles. SketchUp being SketchUp, I guess.

I’m hoping to resolve this without redrawing, because I can’t just increase the segment count of the main cylinder alone; I’ll have to redraw that entire model in order to avoid mismatched circle interfaces, and I’m incredibly lazy.

What seems kind of weird to me is that I have other models with cylinders-intersecting-cylinders and they do not have the same issue. Maybe it’s due to the length of the larger cylinder in this instance?