Boolean Modifier Not Working

I’ve just put in Blender 2.90.1 and was previously using 2.83.1 on an iMac using 10.14.3.

Often I have no problem at all using a boolean modifier, but sometimes it’s a mess and doesn’t behave like it should.

When I’ve done tests and it works, I did this:

  1. Created a sphere mesh
  2. Created a cube mesh
  3. Set the cube mesh to show as wire frame so I could see what was going on.
  4. Move the cube to intersect with the sphere
  5. Selected the sphere
  6. Added a boolean modifier
  7. Used the eyedropper tool to pick the cube as the modifier
  8. Tested the 3 options (Difference, Union, Intersection)

When I do that, it works perfectly.

I need to do the same with a post (this is part of a deck design). So I do the above, but add steps:

  1. Create a cube mesh
  2. Rename cube mesh to TestPost
  3. Transform TestPost to make it 12’ high and 7.5" x 7.5"
    3a. Use CTRL-A to apply changes so that the scale is still 1 in every dimension. (I label this “3a” because I’ve done this in some tests, not in others. It doesn’t seem to make a difference.)
  4. Translate TestPost to a spot far enough from my main project the other objects won’t be near it or show in screenshots.
  5. Create a cube mesh
  6. Rename new cube mesh to ModCube
  7. Transform ModCube to make it 11.25" high and 4.5" wide (Y axis) and leave the X size the same
    7a. Use CTRL-A to set scale back to 1 (done in some tests, not in others - makes no difference)
  8. Modify ModCube so I see it as a wire mesh so I can see what’s going on.
  9. Translate ModCube so it fits in the notch I want to make in TestPost
  10. Select TestPost and Add Modifer (specify boolean)
  11. Use eyedropper tool to pick ModCube as modifier.

At this point I have troubles. The Boolean Modifier option (or mode or whatever) defaults to Difference. Once I pick ModCube as the modifier, this is what I see (with Difference selected):

(And, yes, MdCube is set to show as a mesh, but Difference is acting like Union.)

This is my first post, so I can’t include another image (mods - if you let me, I’ll edit and add the other two images. For Intersect, ModCube is all gray, as if it’s the output.

For Union, only TestPost, and ALL of TestPost is the output.

So Intersect and Union gives me an output I shouldn’t get for any of the 3 operations and Difference gives me what I should get for Union.

Also, those extra edges you see on TestPost show up as soon as I select ModCube as the modifier to use.

From what I see, the difference is that I transform TestPost and ModCube, both, and resized them. I don’t do that with my other test objects. I thought it might be an issue with their scale, so that’s why I tested them with and without resetting their scales.

What do I need to do to make this work?

I have to add, after more experimentation, that it doesn’t seem to be related to scale. I forgot that I was using the 3D cursor to place objects. I’d snap it to a point on TestPost and make that the origin for that object, then snap it to a point on ModCube and make that point the origin. Then I’d snap the cursor back to the origin on TestPost and then select ModCube and snap it to the cursor.

Something about the snapping or having the origin for both objects in the same place seems to be the issue.

It looks like you have faces on one piece that exactly line up with faces on the other. The boolean in 2.90 is not intended to work in such a case. There is a new boolean in 2.91 that is intended to work in such case (the Exact solver).

Do you mean 2.91 or 2.90.1? I just downloaded the latest version yesterday and it’s 2.90.1 - and has almost the same issue. Things look a little different, but it’s still an issue.

I mean 2.91 alpha, which you can get here:
2.91 is not yet released, but the alpha is reasonably stable.

Could I get you to give me an explanation on the difference between 2.90.1 and 2.91 in terms of the numbering system? Is just one decimal used for alpha and beta releases? Like 2.xx is always non-production, but 2.xx.x is what that version becomes when it is moved to production?

Thank you for the link. For now, I will work with the knowledge of this issue and use modifiers that are big enough that I don’t have to deal with the coplanar issue. I am still so new to Blender that I really need the stable version so I don’t get confused by different issues along the way. I like helping test software, but, for me, I feel like I have to know the program and be comfortable with it before I can be at all insightful about bugs or issues.

The production versions of blender last released was 2.90 and then some critical bugs were found so they released a slight modification of that, with fixed bugs, as 2.90.1 . There may even be a 2.90.2 .

The next release (due about Nov 6) will be called 2.91 . It is currently in a polishing/bug fix phase up until then.

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So if I can wait until Nov. 6, the fix for this will be in there? I can work around it until then.

Thank you!

Or you can download the 2.91 alpha now. It should be stable enough for a normal user and has the boolean fix. It is just not recommended to usethe for a production.

Thanks you - for both the time and help!