Hi Scall, could you please post the 3DM model file as well so I could take a look at your geometry instead of just a screenshot? That tends to help a lot to give you more accurate answers, because a lot of things depend on how your geometry is structured and it's hard to tell some things just from a screenshot.

But most likely what has happened is that the 2 objects that you are trying to boolean union together are probably not closed solid volumes and are open surfaces.

If you are working on open surfaces, then you generally need to use the Trim command to cut them with each other, the boolean commands are focused on working on solids.

Both Trim and the booleans do a similar job of cutting things up, but with the Trim command you manually pick which cut up fragments you want to discard or keep, and then you can use Join as another step after that to glue together surface pieces that are touching.

Booleans also cut things up, but they automatically decide which pieces to discard and which to keep based on which volume the pieces are contained inside of, like with boolean difference pieces that are contained within the cutting volume are removed. But if your objects do not actually enclose a volume and have open ends or stuff like that then the boolean commands won't really be able to function properly.

It can actually be easiest to close off each separate object that you make to make it into a solid first before you work on combining them together, that way you will be able to use booleans to do the work and that usually saves some steps that you would have to do manually with Trim + picking pieces to discard + Join. Basically booleans are sort of like a batch mode operation of doing cutting plus discarding plus joining for you automatically but you have to have a solid in order to make use of them.

Hope this helps - if you can post the 3DM model file it would definitely make it easier to better diagnose what you are running into instead of just guessing though.

- Michael

Hi Scall, so looking at your screenshot a bit more closely it looks like your smaller upper piece is not a solid - it does not have planar ends and so it would not get an automatic end cap put on it if you made it with something like sweep for example.

To get something like that as a solid, it's usually easiest to first model a more simplified type of block that has planar ends something like this:



So the good thing about starting with this initial shape is that it is a solid right from the start, things with planar ends get a cap placed on them so they are a closed solid.

Now to make non-planar ends, you can draw in some profile curves from the side like this:



Then use boolean difference to cut the solid with those curves, it will slice up the solid into smaller solid pieces (leaving the "side walls" of the cutting curves imprinted in), and then you can select the pieces you don't need and delete them:





This is kind of a recurring strategy to try and reduce the amount of individual surface creation - try to build a kind of more simplified solid block piece as your starting shape and then cut some pieces of it off with booleans rather than doing a totally non-planar non solid piece to start with - if you do it that way you're doing all surface modeling only instead of using solids and you will be using a generally more difficult workflow.

Also see here for some similar information on how to imprint more customized kinds of end caps onto solids as well - you can model a swoopy surface and then use the surface as a cutting object to cut the solid up if you want a more custom contour than what the silhouette of a 2D curve will give:
http://moi3d.com/forum/index.php?webtag=MOI&msg=5012.7

- Michael

Also if you are coming from a polygon modeling background, see here for some info and tips for the different kind of strategy that you use for NURBS modeling:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2

- Michael

Michael

many thanks again

You were exactly right. The smaller peice is not an upper solid. I was trying to create this peice (using curves and mirror) on the surface of the torso so the matching was exact. When i lofted the peice it did not cap. So, I have created another peice, which is solid and did cap and then moved that to the correct area and then union it worked! I had to rotate and scale a little to align, however it did work well. I wonder if their is an align to a surface tool? Next bit of work :)

Really starting to enjoy this now...hopefully enough I can justify paying for it at the end of my trial.

Scall

and thanks for the tips - most usefull

Hi Scall,

> When i lofted the peice it did not cap.

That would be because the ends were not planar - MoI only knows how to automatically seal off planar ends of shapes, if the end is warped or bent around in 3D instead of planar it will remain open and you will have to find some other way to seal it off. Usually the easiest way to seal off an end though is to slice it off with some other shape that extends through it by some amount.


> I had to rotate and scale a little to align, however it did work well.
> I wonder if their is an align to a surface tool?

There are some tools for orienting an object onto a planar surface, check out the Transform > Orient tools, some more information here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4487.61

- Michael

thanks again