Hey guys,
I want to model a bicycle rim. I know that there are sometimes issues with boolean union, but I don´t know how to fix it. I tried many hours. I created the rim and now I want to add little rings for the spokes. But I cant union them together to one solid. Sometimes I can union some, and others not. When I open moI again, I can union one, and others not.. I don´t know how to fix it. I also tried first to union the solids together and did the b. diff afterwards, but then I get just a joined surface...
So, I tried many things, but I don´t know how it could run...
Maybe I am using the tool the wrong way?

I hope you can help me,

best regards from Hamburg

Koi

Without the 3dm file it's difficult to answer!

Generally pieces must be enter inside very frankly!

If your file is top secret you can send to michael : moi@moi3d.com

sure, I know. At the moment it is not possible, its just loading.. I will try it again tomorrow :)
Thanks for the fast answer!!

rotate the cylinders so the construction lines don't line up with the base object's?

Hi Koi, yes I'll need the .3dm model file to be able to give advice on what might be going wrong.

- Michael

Hey guys,
sure, I´m sorry. Now I got it:)
i got one more question: In the data is a second object. I made a cut with b. diff. with an freeform curve. Now i made a new surface with network to get a solid again. I´d like to b. union the surface and the cut object, but it does not work. I think this is a real nooby question;)

Thank you guys so much!

For boolean something (volumes) blocks must be intricated, (surfaces) must have a part of an commun edge!
But you can't Boolean Volumes with Surfaces!

Hi Koi, is it this one here that you're talking about? (there are 38 objects in your file so I'm not entirely sure):



In general the booleans are meant to be used on solids, you can use a surface as a cutting object in a boolean when the surface divides it into pieces but you can't try to glue on an open surface to just one end of a thin-walled solid like you're trying to do here. It's not able to form a solid out of that combination, there would be no thickness at the top.

If you want to erase the wall thickness the best way to do that would be to delete the inner wall surface and end caps and use Edit > Separate to break this surface off to an individual surface:


Now with that surface not joined to any other one you can select all of its edges (select one edge and then Ctrl+A)
and hit Delete to "untrim" it and recover the full underlying cutting surface:




Now select all the edges of the cylinder surface and hit delete to untrim it too:





Select the cylinder and run Construct > Planar to make it into a solid with the planar ends being capped, and then you can use boolean difference to cut it:



Hope that was what you were wanting to do, I've attached a .3dm file of the result.

- Michael

Hi Koi, just as some additional explanation on why boolean union wasn't working for you - if you have a solid with "wall thickness" like this:



then it's not going to work to try and insert just one open surface across the top of it:



that won't make a volume because there would be no thickness in that top area. Instead of just one surface draped over the top if you formed an entire solid plug to boolean union in that could work but for restoring cut away areas it can be better to do "untrim" instead, there is some more info on untrim here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=444.4
http://moi3d.com/forum/index.php?webtag=MOI&msg=9671.5

- Michael

Hi Michael,

thank you so much! Your support is great, I take you as an example!

Now I definitely understand, thanks for the links to the older posts.
Sorry for my bad english by the way..

I got one more question, I will send you the data.

I want to build a rim for a bicycle. I made the rim and now I want to add little rings for the spokes. These are all solids but I can´t b. union them together.
Can you tell me why?

And second: A friend told me, sometimes it works when you start the program again. He does it sometimes with b. union problems with rhino.
With another little problem it worked with Moi3D as well. But this time not...

Michael, thank you so much and have a great day!

Koi

hi Koi, it's probably because the pieces are not quite fully aligned with each other, there is a sort of really thin slivery "shelf" like shape that would need to be created by the boolean. Things involving skinny fragments like this can make things difficult for the boolean intersection calculations:





I'll take a look at it some more later to see if I can give you any suggestions.

- Michael

Probably the best bet would be to scale the ring pieces slightly up or down so that they will have a simpler and cleaner intersection with the main piece without any sliver thin pieces getting created.

- Michael

Hi Koi, here's a version with those pieces booleaned in now. I scaled the rings slightly so they had a better intersection with the surrounding geometry.

3DM file attached.

- Michael

Hey Michael,
I understand... Thank you so much!! Also for sending me the right object :)

Thank you again and have a nice day!

Koi