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I am taking a Bezier curve, turning it into a mesh, then mirroring it on the X axis and joining the two meshes, then I mirror it on the Y axis and join them. I merge the vertices where the joints were made, then create a face and make a prism out of it. Then I duplicate it (part of my process to be sure I keep the original one) and move it so it goes through a cylinder and try to apply a boolean modifier (using the Difference option). But the boolean modifier does nothing.

Here's a screenshot of what I'm working with: enter image description here

The lower left item is the bezier curve I'm working with. (The original. I created a duplicate to work with.) I turn it into a mesh. From there, I have tried duplicating and mirroring with CTRL-M and I have also used the Mirror modifier. (In both cases, of course, I have to use the 3D cursor to change the object's origin so I can do the mirroring properly.) I have tried this mirroring the X axis first and the Y axis first.

I have also varied creating the face or faces. I have created a face once I have one mesh going all the way around, then extruded. I have also extruded, then created both the top and bottom face separately.

No matter what I do to take this Bezier, convert it to a mesh, create the shape I need by mirroring it twice, extruding it, and adding a top and bottom face, once I move it into place and try to modify the cylinder with it so I have a hole in the cylinder that matches the prism shape, it will not work. Nothing happens and the cylinder is not modified at all.

What am I doing wrong and why won't this prism work as an object for the modifier?

Blend file:

(Note - adding the .blend file once I have the URL for this question for Blend-Exchange. If there's a way to do that before posting the question and editing later, I'm open to it.)

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  • $\begingroup$ Sometimes the Exact solver doesn't work. Try switching to the Fast Solver. It works on your object in 3.2.0 at least. $\endgroup$ Commented Jul 1, 2022 at 22:47
  • $\begingroup$ @MartyFouts Do you want to write that up as an answer? It works. Do you have any idea why it doesn't? (And for documentation purposes, I'm using 2.92.0 - haven't been able to use Blender in at least a year. I REALLY have to upgrade!) $\endgroup$
    – Tango
    Commented Jul 1, 2022 at 22:51
  • $\begingroup$ The normals are inverted on your boolean object. If you reset them in Edit mode with SHFT-N it works fine even in Exact mode. $\endgroup$
    – John Eason
    Commented Jul 1, 2022 at 23:47
  • $\begingroup$ @Tango Perhaps you could ask John Eason to write up an answer that mentions both checking normals and trying the fast solver? If he doesn't want to write an answer, then I will, with an explanation of how the normals matter. $\endgroup$ Commented Jul 1, 2022 at 23:53
  • $\begingroup$ @JohnEason - Did you see Marty's suggestion? So all I have to do is select that prism, go into edit mode and hit SHIFT-N? - Okay, just tried that. Duplicated the object, dragged it into place, hit TAB to get to edit move, hit SHIFT-N, and went back to Object Mode. I didn't see any marking indicating it worked in Exact mode, so I changed to Fast mode and it worked there. $\endgroup$
    – Tango
    Commented Jul 2, 2022 at 2:52

2 Answers 2

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The normals are inverted on the modifier object. Turn on the Face Orientation overlay as shown below. enter image description hereAs @MartyFouts says, using the Fast Solver option in the Boolean modifier does work in this case but for some reason it also flips the normals on the main object as shown below:enter image description here Select the modifier object. Go into Edit mode and select All. Then hit ⇧ ShiftN to correct the normals. enter image description here Back in Object mode, hide the modifier and you'll see that it's worked correctly in Exact mode.enter image description here Hint: Enable the Bool tool addon and you can use shortcut keys to add modifiers and turn on Wireframe in its preferences. Makes life much easier!

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  • $\begingroup$ You just went through a thorough and expanded version of what was in your comments. I can't figure out why, but it didn't seem to work yesterday and works today. Honestly, I think I have to put that down to user error! I made a dupe of the prism, so I wouldn't mess it up with any mistakes, and moved it into place, did what you said, then went back to Object Mode, picked the cylinder and added the modifier. As soon as I picked the prism as the modifier, I could see the outline of the cut in the cylinder in Exact mode. Thank you! Any idea why the normals were inverted? $\endgroup$
    – Tango
    Commented Jul 2, 2022 at 19:41
  • $\begingroup$ It's quite easy to get normals inverted without realising to be honest. To demonstrate, add a plane to a new scene, turn on the Face Orientation overlay and in Edit mode, first extrude the plane up then undo with CTRL-Z and extrude it down! $\endgroup$
    – John Eason
    Commented Jul 2, 2022 at 21:01
  • $\begingroup$ Thanks for that and all the other info on this! There is still so much I'm learning just to create and manipulate objects - and I haven't even come close to trying to animate! This started as frustrating but I've learned something useful! $\endgroup$
    – Tango
    Commented Jul 3, 2022 at 1:22
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I realize you didn't ask for it now, but I just felt like rebuilding the thing with Geometry Nodes.

...Maybe it will help you.

The practical thing is: It is 100% procedural!

So you can always edit the mesh non-destructively.

The only starting point is the curve you created (note the center of the curve).

enter image description here

Basically I do exactly what you have done step by step so far:

  1. I duplicate the curve so that I get the desired shape.

  2. I create a filled polygon from it

  3. Then I extrude this shape

  4. I also create some cylinders in different sizes

  5. And finally I use the node Mesh Boolean to cut the parts.

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  • $\begingroup$ I'm curious. How much longer did it take you to create that node tree than the 20 or so seconds it took me to create the geometry? $\endgroup$ Commented Jul 2, 2022 at 17:13
  • $\begingroup$ ....honestly I have no idea, but time is relative :D $\endgroup$
    – quellenform
    Commented Jul 2, 2022 at 17:15
  • $\begingroup$ It might be for some folks, but others have a life! :^) $\endgroup$
    – John Eason
    Commented Jul 2, 2022 at 18:03
  • $\begingroup$ Time may be relative, but when you're setting up something that will eventually be part of how you're paying for the rent, it's a big issue. Thank you for the work and information, but there's no way I can spare all that time every time I create a new shape I want to use for a new pottery extruder die. $\endgroup$
    – Tango
    Commented Jul 2, 2022 at 19:26
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    $\begingroup$ Fair enough. Sadly a lot of long-time Blender users are put off learning procedural nodes because they don't think they'll understand them. $\endgroup$
    – John Eason
    Commented Jul 2, 2022 at 21:06

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