Hi All

Quick over view:
trying to modal a chess board, it's 284mmx284mmx10mm, it has a 10mm board and 33mm squares.
I want to have all "black" square recessed 0.7mm.

So here is wat I did.
First I made the base board via a cube, entering the dimensions, no extruding or resizing.
then I made up a 33mmx33mmx2mm solid has a die. I place this so it sat .7mm into the base board, run a boolean->Diff , with option remove unchecked, when I take away the die, I'm left with a nice .7mm recess has expected.

So I layout the 31 other dies, I remove 7 other dies no problem, but after that when I try to Bool-Diff more dies, it's removing the face of the base board and I can "see" inside the board instead of leaving a recess. I don't know what's going on, what cause a solid to be come hollow?
I restarted the model 3 times but the same thing keeps happening, so clearly I'm doing something wrong, but have no idea what it is.


I've attached my model, if some could please have a look? I'm trying to diff out the red squares and then hollow out the material underneath

Thanks Steve

Hi Steve - so your main base piece has become a "Joined srf" instead of a fully closed solid - it has some openings in it and booleans will behave differently when done on an open surface object instead of a closed volume.

You can see whether an object is a solid or not by selecting it and then looking at the type indicator which shows up in the properties panel in the upper right area of the model.

I suspect that your problems are coming from having 2 cut out areas just kind of exactly graze each other along a shared edge in these areas here:



By having those 2 adjacent recessed areas exactly graze each other at a shared edge like that, it would basically require that one edge there to be shared by 4 neighboring surfaces instead of only being shared between 2 adjacent surfaces. That's called a "non-manifold" edge and MoI tries to avoid making those kind of edges - when a boolean result would cause a non-manifold edge it tries to go through the model and decompose it into different separate chunks so that there are not any non-manifold edges in it anymore - it's that process that is likely causing you problems.

It's usually best to avoid creating things that exactly graze each other in such a way to make that kind of non-manifold situation - is it possible for you to slightly shrink the cut out area so that there will be a tiny bit of area between the corners of the 2 recessed spots?

You might kind of think about the current exactly abutting recessed areas as having created a zero width area of the model (at the shared edge) and that's what you will probably need to avoid to make it work well.

- Michael

Or I guess the other way you could do it would be to make the recessed areas slightly larger so there was a little bit of open space there where their corners run into each other rather than each corner touching the other right along a single edge.

- Michael

thanks , Michael

I'm working in mm how small a gap can I make, would .01 mm work?

Cheers, Steve

Hi Steve,

> I'm working in mm how small a gap can I make, would .01 mm work?

Yeah that should likely be ok.

- Michael

making sure there where gaps between object did the job.
thanks. Michael.