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I'm new to blender and I'm trying to make a sphere with a 40 degree cut from the top to the front. I'm using boolean operation to do the cut but I'm having difficulties turning the triangles on the side into quads. (I heard that this will cause issues to the subsurf modifier)

enter image description here

The small triangles can be dealt with by simply merging them but the bigger ones are the ones I'm having trouble with.

enter image description here

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  • $\begingroup$ did you try merge by distance? $\endgroup$
    – Chris
    Sep 26, 2021 at 9:51
  • $\begingroup$ I have tried but I could not reduce the triangles into quads. There will always be triangles no matter how I merge. $\endgroup$
    – Vector
    Sep 26, 2021 at 11:47
  • $\begingroup$ If the cut is made along a latitude and then sphere rotated would remove issue of tris and 5-gons. $\endgroup$
    – batFINGER
    Sep 26, 2021 at 15:09
  • $\begingroup$ The thing is this shape should also have a flat bottom as well. $\endgroup$
    – Vector
    Sep 26, 2021 at 15:36

2 Answers 2

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From a cylinder.

enter image description here

The thing is this shape should also have a flat bottom as well.

enter image description here

If add a sphere for reference, then a default cylinder and shrinkwrap the cylinder to the sphere.

Grab the top face, or top edge ring and transform. In GIF example have simply scaled arbitrarily in Z and rotated top face about its median point 40 degrees. Adjust this to suit.

Then CtrlR Loop cut and slide

Exited edit mode, applied the modifier.

Could also be done similarly with one of the to sphere options..

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    $\begingroup$ Thanks you so much for this lovely guide, I tried to replicate it and this is the result. Are the lines supposed to be this jagged? i.sstatic.net/GNHFZ.png $\endgroup$
    – Vector
    Sep 27, 2021 at 15:06
  • $\begingroup$ Quickly slapped together another, this is result pasteall.org/pic/de442b27e08a40759be876a41760d0ba Did you use Target Normal Project as modifier method? $\endgroup$
    – batFINGER
    Sep 27, 2021 at 15:27
  • $\begingroup$ I did. I see from your picture the top is slightly twisted. I think thats where I messed up cause I tried to straighten that top which might have mess up the loop cut. $\endgroup$
    – Vector
    Sep 28, 2021 at 1:39
  • $\begingroup$ I'll try again to do the loop cut first then adjust the top and report back the issue. $\endgroup$
    – Vector
    Sep 28, 2021 at 1:40
  • $\begingroup$ Do the loop cut last. $\endgroup$
    – batFINGER
    Sep 28, 2021 at 1:41
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The usual workflow is to edge slide (shortcut: select the vertex and type GG. Type Enter when done.) one of the vertices along the circle until it reaches another one nearby and then to merge by distance to create just one node.

For example, your leftmost circled problem can be fixed by doing this twice. First edge slide the upper vertex in the circle to the one below it. Then slide the vertex that's in both circles to the one that's only in the middle circle. select all and merge by distance, and that's solved.

Unfortunately, this won't work in some case. Having done that, your middle circled area is still a triangle. Some people suggest subdividing the edge that is the circle part of the triangle. Other's suggest not bothering. It depends on how bad the triangle affects shading.

Sometimes you just can't fix the triangles without adding more geometry than necessary.

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