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I'm designing a real object: a cylinder box dispender. It will be 3D printed: two mirror versions of the same object (named Half.shell) will be printed and then screwed or glued together. Just before gluing/assembling these two parts, I want to insert a thin band of metal between them, and give it a spiral form, so a spiral groove must be made available in the Half.shell object. Context is Blender 2.9.1 with extra curve add on. The problem I have is when I want to make the spiral groove into Half.shell object. I've built a spiral of cubes, starting with a cube, add modifier array of 780 objects, then add modifier curve following an archemedian spiral curve created with the extra curve addon. I've tried boolean modifier as well as BTool addon to make the difference/groove, with no success: the resulting shape is a real mess with triangles going everywhere and nothing becomes editable from this point.

Edit1: -the Spiral.of.cubes object sometimes grows by itself, as if I've scaled it on the X & Y axis, and reopening blender can help, but not always. This problem occurs when I'm changing selection in object mode and edit mode. -so may be the way I'm doing the spiral.of.cube is not the good way. -Spiral.of.cube is in fact a spiral of parallelepiped 1.5x1.5x2mm

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  • $\begingroup$ Hello, so what are all these cylinder for? I guess your problem is just between the spiral and the shell? Just to make sure... $\endgroup$
    – moonboots
    Oct 30, 2020 at 8:53
  • $\begingroup$ Yes, you can hide or delete them. They will be real world objects (jars or something like that), so I've drawn them to check they fit into the inside of the spiral. $\endgroup$
    – vibi27
    Oct 30, 2020 at 9:04
  • $\begingroup$ there are several problems like for your spiral inner faces and overlapping vertices, that's easily fixable before applying the modifiers if you delete 2 faces of the cube and click on the array merge option, but your shell has also bad topology like inner faces, overlapping faces, flipped normals, you need to fix that and the boolean will work much better $\endgroup$
    – moonboots
    Oct 30, 2020 at 9:25
  • $\begingroup$ also you should probably simplify the topology of the flat surface of the shell (where the boolean will happen), it will probably help $\endgroup$
    – moonboots
    Oct 30, 2020 at 9:33
  • $\begingroup$ Thank you. When saying boolean modifier you mean regular/default blender boolean modifier or BTool add on ? $\endgroup$
    – vibi27
    Oct 30, 2020 at 9:36

1 Answer 1

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What you need to do :

  • Select your spiral cube object, delete 2 faces so that it won't generate inner faces, apply both the Array and Curve modifier, press Alt > Merge By Distance:

enter image description here

  • Fill each tip with F :

enter image description here

  • The topology of you shell is messy, go in Edit mode and press Alt > Merge By Distance, in the Operator box choose a Merge Distance of 0,001 :

enter image description here

  • But you also need to delete inner faces, overlapping faces, and you need to recalculate the normals (AltN), especially if you plan to print in 3D.

  • Once everything done, you can merge all the faces of your shell surface, where the boolean is supposed to happen:

enter image description here

  • The Boolean will work fine:

enter image description here

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  • $\begingroup$ Your help is really appreciated. Thanks a lot. $\endgroup$
    – vibi27
    Oct 30, 2020 at 10:04
  • $\begingroup$ Some additionnal questions: To Compute normals: Edit Mode->Select all->Alt N->Recalculate outside ? $\endgroup$
    – vibi27
    Oct 30, 2020 at 11:02
  • $\begingroup$ Yes, also, check the normals: open the Viewport Overlays panel and enable Face Orientation $\endgroup$
    – moonboots
    Oct 30, 2020 at 11:05
  • $\begingroup$ Thanks a lot, you saved me days. Hard for me to check this toggle since all menus are transparent (graphic card is an old ATI from 2012, seems to be no more supported in new versions of blender...) and this region is full of static information underneath, $\endgroup$
    – vibi27
    Oct 30, 2020 at 11:17
  • $\begingroup$ So maybe use a previous version of Blender, Boolean has been improved in 2.91 but it should work with 2.79 $\endgroup$
    – moonboots
    Oct 30, 2020 at 11:23

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