Why do circles sometimes not properly cut into existing faces

Sometimes if i draw a circle on an existing face, if does not divide the face, but layers an extra face on top instead (if both faces are oriented the opposite way around, the two colors flicker through each other)
But i can proof, that the circle is perfect lined up on the face by removing these faces, leaving only the edges and than draw a line along a circle-segment.
after this the circle is properly integrated as an edge in the face.

Why does this happen sometimes?

The last times i noticed this, as i created an edge from the face-border to somewhere mid-face (death end, line looks thicker) and than use this free line-end as midpoint for the circle.

What version of SketchUp? Please complete your profile.

Do you have Length Snapping enabled? Can you share an example where this happens?

I use sketchup make 17 because there came no more desktop versions after it.
It happens in various situations.
And not only with circles directly from the circle-tool

Now i used this self modeled tool (active group in the image):

and “intersect faces” (the tool is here already aligned to a kite-shape to modify ti) to place the face-details on the tilted faces of the kite-shape

Here is the result (i already made a bit continuing work on it):

The with push-pull stretched eye-shapes of the tool-object are open at the bottom because eyes and pupils share the same line-segments at the bottom most point.
I had to draw these segments by hand.
The eyes where properly included into the geometry before, but at finishing the bottom line-segments for the eye-shape they popped back out like one still is in this picture, that also has a second layer of surface (i already repaired the other, what proofs, that they are absolute plane in the surface).

I can easily repair these things by deleting the outer surface and recreate it by redrawing a line-segment of the inner shape.

That’s not true. There are no more Make versions, of course. Put that in your forum profile.

Share the SketchUp file. Looks like you just need to get all of the faces in the same context first.

I taught, i said sketchup make.

What do you mean with face context (the eye-shape is part of the group of the kite), and i already repaired the eye-shape there.

I know, how to fix these things, i´m just curious, why they happen.

You did. Please complete your forum profile.

From your screen show the geometry is in different groups (contexts). It needs to be in the same context.

Errors in modeling workflow is the common reason.

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the eye-shape is not in a different group or component.
I created it while inside the group of the kite-shape.

You have not shared the model so all I can do is go by what I can see in your screenshot which isn’t enough.

It´s already fixed in this model. Maybe i send you one, if another one happens.

Another one happened
kites.skp (215.5 KB)
It´s on the third kite at the eye, that i already closed at the bottom but this time no thicker outline, only stacked faces (i moved the tool-object already to the fourth kite)
i. use the tool-object and “intersect faces” - New geometry appeared properly included in the surface.
2. hand drawn the bottom line segments of the eye.
this step added extra layers of face inside the eye (if you select the triangle around the eye, the honeycomb-selection-pattern also appears inside the eye)

Just for a test i closed and reopened the file in this stare and got this:

The grey stuff, that goes from the eye to the side corner, flickers, if i turn the camera.

Okay, first thing I’m noticing is that this projection isn’t symmetrical.

See how the circles converge on the same point on the left while they’re slightly offset on the right.

One of the reasons you’re having intersect problems like this is you’ve got too much overlapping geometry.

This has even led to some broken geometry in your extrusions, which you mentioned having to manually repair.

Maybe you should intersect the face in stages rather than all in one go. For example, you could extrude and intersect the outside of the eyes first, make sure everything is lined up properly, and then do the pupils as a separate pass.

I knot that al ready, that is, what i close by hand and after doing this i have extra layers of surface appearing.

You’re having to do that because Make doesn’t have a weld function. Your circles are breaking into individual line segments, that’s why they’re segmented when you extrude them outward.
If you want to avoid conflicting geometry, you should redo the 2D version of the face to make sure your circles aren’t breaking up into segments.

I don´t mean the segments on the extruded things, i mean the result on the other kite-shapes.

You’re getting those results because of the broken segments.

the small circles on the cheeks are not broken into segments, but sometimes i got that result there too.

And i already got such weird behavior by constructing the circles into the 2d face and i only was able to fix the multi layered faces by redrawing a segment of the circles and that caused that breaking.

That’s another problem. Right now, the holes in those cheeks are empty rather than colored over like the others.

You’ve gotten the gray patches on unbroken circles after intersecting?

That is because it´s actually a concept art for mascot-costumes and it should be the holes for the hands.

My mistake. Thank you for clarifying.

As I asked, when you’ve intersected the unbroken circles into the face, have you also gotten those gray patches?

the grey patches where only in that specific situation, where the screenshot was from.

but for the hand-holes i just meant, that sometimes the face inside the circle was just added on top as another layer instead of being something, that i just could delete to get a hole there