# How to fix boolean cut failures?

I refer to the Blender built-in boolean tool described here.

I am cutting a complex surface > 30 000 facets. All the cuts are along coplanar surfaces. About 50 % of the cuts fail.

In the detail of the cut file posted, you can see that the boolean cut seems to be done, but that the tris are not removed.

What can I do to ensure that the boolean cuts do not fail, or is there an easy way to remove the tris after the cut failed?

See this large sample cut file.

Overall shape

Detail

Thanks.

• Hello and welcome :). Would you mind adding one or two images? For those of us with bad imagination. Jan 27, 2020 at 13:27
• @ᴊᴀᴄʜʏᴍᴍɪᴄʜᴀʟ added a sample file. Jan 27, 2020 at 17:02
• @ᴊᴀᴄʜʏᴍᴍɪᴄʜᴀʟThanks for generating the detail. Jan 29, 2020 at 13:03
• You can upload your .blend file here: blend-exchange.giantcowfilms.com Jan 29, 2020 at 14:10

To repair this kind of damage I would select all and press X (Delete) to start from scratch.

Very similar result you can get easier without booleans and with clean topology by shrinkwraped edges over your terrain.

• Add plane, slice it by Ctrl+R with value of desired amounth of cuts
• Select one short edge, search for Select Similar > Lenght and delete them (X)
• Subdivide all long edges in amount of desired detail
• Rotate in desired angle of Z axis
• Add Shrink Wrap modifier with Projection type, Target your terrain, Z axis, Positive, Apply
• Select all vertices, Extrude (E) in Z axis, move below terrain level, Scale in Z to 0
• Add Solidify modifier to get thickness

Simplified sketch of proces

Hires model (1000 slices)

• I also needed some non-manifold culls. The main challenge that remained was to add a solid base at the bottom. A 0,1 mm overlap ensures no co-planar fails with a boolean union. Feb 4, 2020 at 19:07

Let me post a new answer, showing how to simply repair the mesh.

1. Select the faces that weren't deleted and delete them X > Delete Faces
2. Select the two side edges and bridge them with a new face Vertex > New Face, F
3. Select bottom edge loop Alt + LMB, and also fill it with a new face F

I'm well aware your mesh is more complicated, but I used the exact same approach to repair two of the errors there.

When the edge is missing in some places, just connect the vertices, before you continue.
Vertex > Connect Vertex Path
Shortcut: J

• I like your examples a lot. It shows the process clearly. If there are no better answers, +50 will be yours. Jan 29, 2020 at 19:14
• Thanks for the feedback, I'm glad you like them :). Jan 29, 2020 at 19:18

CTRL+T works in edit mode to triangulate the mesh. Blender boolean operations function best on triangulated mesh, so doing this will improve your boolean. One more thing: you may want to do a limited dissolve function on the boolean being cut, so that the operation does not take so long. (Before CTRL+T).

• Do I triangulate both solids before I do the cut? Jan 30, 2020 at 9:34
• Just the one being cut. Jan 30, 2020 at 13:26
• Nope it also fails. Edit ctrl-X ctrl-T improves the speed but the fail remain. Thanks for the effort. Jan 30, 2020 at 18:23
• I will keep ctrl-X ctrl-T and try the other answers. Jan 30, 2020 at 18:59