# Boolean operation on two objects in Blender

I'm trying to draw a strange cup, with a kind of empty handle (actually, it's not a cup, but it looks like one).

I need to print this object with a 3D printer, so I exported the model to 3D printing software (Simplify3D) to obtain relative G-code for the printer.

I can correctly export (in .stl) both parts separately (cup [a] and handle [b]), and obtain a good G-code. But when I try to match the two parts with a boolean operation, the result becomes chaotic.

I've added a (G-code) picture to show how the slicer creates strange triangles inside the cup; I really can't understand how to prevent it.

I'm designing the print using the Blender 3D software modelling tool.

I've uploaded my file for reference.

The file has the bezier curves from witch I do screws in the origin. the result that I'm trying to export in stl is on the side. Note: to have correct dimensions, I scale the model after 90° rotation on x-axis (base on bottom for printing), I then change the scale to 1:10 (bigger model), before exporting as stl.

I would obtain a sort of vase with an empty handle (the cylinder should work as an hole).

here what I do:

1. I convert curves to meshes
2. I screw the cup (360° y-axis)
3. I screw the handle (60° after rotation -30° on y-axis)
4. I solidify the handle
5. I add 2 operations to cup, (a) solidify, (b) boolean
6. to match the two solid I adjust the solidify (a) looking to boolean result of an intersection (cup to handle).
7. when I have the right overlapping I apply (a) solidify and then (b) union-boolean (cup to handle).
8. at the end I apply a difference-boolean modificator to cup/handle with cone, to create the hole.

I hope someone should explain me what I am doing wrong. I have made a somewhat simpler version here.

• Answers could be better if you share the messed up model and G-code btw. – Trish Feb 12 '19 at 12:54
• Make sure there are no "rogue" vertices in your handle part before combining. I don't know Blender, but I do know that in MeshMIxer, Boolean operations only work after running the "Make Solid" command on the parts to ensure proper Boolean logic. – Carl Witthoft Feb 12 '19 at 16:10

## 1 Answer

Check your settings in the slicer software you use: if you look at the sliced print carefully, you see only one line in each layer that crosses the inner section. The lines are also yellow, not green. This strongly hints that these are movement commands, not actual print commands.

On the other hand, you might want to carefully check in blender: at times, the normals in places get swapped inside out and then mess up the whole geometry without being visible in blender. Recalculate Normals can fix that at times, other times choose the messed up vertices and flip normals.

Make sure not to include voids in the model.

## The model in question

Looking at the model, I also spotted that there was a lingering solidify modifier. Applying that resulted in this:

This is a particularly bad thing. Fixing is easy though: remove the offending inner vertices.

Atop that, the center points are a clustered mess of vertices - surely you want to merge them into just two vertices.

Applying the Boolean modifier now created a solid shell.

Before exporting, all other items had to be removed (deleted), then the export gives this nice model:

• I cheked the slice, they are not only movement, infact they are filled iside. – Marco Feb 19 '19 at 18:05
• I also recalculated normals but it still remain the error.. I have no idea, I drawed this project so many times.. please help.. (and tank you for suggestions) – Marco Feb 19 '19 at 18:06
• @Marco then please share the model – Trish Feb 20 '19 at 1:02
• I added a link at the end of question. – Marco Feb 20 '19 at 8:27
• @Marco I did what I could... and came up with a perfectly fine model with just a few little tweaks. – Trish Feb 20 '19 at 14:04