Hi Mike,

> Objects disappearing is often an unsatisfactory result of the Boolean commands.
>
> I'm not sure why, but I do know how to quickly work around this problem:

It will happen if some of the objects involved in the boolean are open surfaces rather than closed solid volumes.

The boolean commands are mostly oriented around working with closed solids, they decide which pieces of things to keep based on which volumes they are contained inside of.

You can use open surfaces in some ways, like as a cutting object to slice a base solid into 2 pieces if the cutting surface fully divides the base object.

But when your base object in boolean difference (the one that you are trying to cut) is not a solid itself which is the case with this example then it will behave more like a Trim operation.

Usually with the booleans you want your base object that is being booleaned to be a solid, so if there are open ends seal those off by getting caps joined on there before doing the boolean.

If you are not able to make the base object into a solid and you want to work at more of a surface level then usually you will want to be using the Edit > Trim command to work at that level - Trim does not try to do things by volume containment, it just dices surfaces up and lets you pick which fragments you want to keep or discard.

The booleans are kind of convenient though because they work as a kind of batch mode of doing a combination of Trim + automatically deciding which pieces to keep or discard based on which volume they are related to + joining the results up. So they can save some time since they incorporate multiple steps like that into a single operation, but if you want to use that kind of batch mode convenience level you do need to get your base object to be a closed solid first before you start to do booleans on it.

- Michael

Here's a bit more explanation on why you get this kind of result when doing a boolean with a non-solid open surface as the base object.

Say you try to do a boolean with this plane surface as the base object and the cylinder as the cutting object:



MoI has no way of knowing which piece of the cylinder it is supposed to keep - it doesn't know whether it should keep this part:



Or whether it should keep this other part instead:



Since it has no way of deciding which piece to keep it does not keep either one and instead will make a result like this:



If you do want to cut objects like this with one another and keep one side of the cylinder part, you would usually want to use the Trim command instead of booleans, it will slice objects up into pieces and then you get to pick which pieces to discard, it does not try to automatically decide based on volume containment unlike the booleans.

Because the original network handle type object had open ends at the top and bottom, it was not a solid and so it behaves the exact same way as this example in this post with the plane - I know that it seems like that handle seemed fairly "solid-ish" looking at first glance, but unless it has a totally connected skin that actually forms an enclosed volume MoI is not able to give any special weight to one side of it or the other side since that would require some kind of more artifical intelligence-like judgement about which side is supposed to be the outside region of it, while if you actually have a solid there is a clearly mathematically defined outside and inside region.

- Michael